Travismulthaupt.com Chapter 47 Animal Development.

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Chapter 47Chapter 47Chapter 47Chapter 47

Animal DevelopmentAnimal DevelopmentAnimal DevelopmentAnimal Development

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The ZygoteThe ZygoteThe question of how a The question of how a

zygote becomes an zygote becomes an animal has been animal has been asked for centuries.asked for centuries.

As of the 18th century, As of the 18th century, preformation was the preformation was the prevailing notion. The prevailing notion. The idea was that a idea was that a preformed miniature preformed miniature infant (homuniculus) infant (homuniculus) was contained within was contained within an egg or a sperm.an egg or a sperm.

The question of how a The question of how a zygote becomes an zygote becomes an animal has been animal has been asked for centuries.asked for centuries.

As of the 18th century, As of the 18th century, preformation was the preformation was the prevailing notion. The prevailing notion. The idea was that a idea was that a preformed miniature preformed miniature infant (homuniculus) infant (homuniculus) was contained within was contained within an egg or a sperm.an egg or a sperm.

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The ZygoteThe Zygote

More than 2000 years ago: Aristotle More than 2000 years ago: Aristotle originally posed the idea of epigenesis originally posed the idea of epigenesis to explain embryonic development.to explain embryonic development.

This idea explained that an animal This idea explained that an animal gained form gradually from a relatively gained form gradually from a relatively formless egg.formless egg.

More than 2000 years ago: Aristotle More than 2000 years ago: Aristotle originally posed the idea of epigenesis originally posed the idea of epigenesis to explain embryonic development.to explain embryonic development.

This idea explained that an animal This idea explained that an animal gained form gradually from a relatively gained form gradually from a relatively formless egg.formless egg.

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As microscopy improved in the 19th As microscopy improved in the 19th century, embryologists began to see century, embryologists began to see that embryonic development took place that embryonic development took place in a series of progressive steps and in a series of progressive steps and epigenesis became the favored epigenesis became the favored explanation.explanation.

The genome of the zygote and The genome of the zygote and differences in early embryonic cells differences in early embryonic cells determine an organism’s development.determine an organism’s development.

As microscopy improved in the 19th As microscopy improved in the 19th century, embryologists began to see century, embryologists began to see that embryonic development took place that embryonic development took place in a series of progressive steps and in a series of progressive steps and epigenesis became the favored epigenesis became the favored explanation.explanation.

The genome of the zygote and The genome of the zygote and differences in early embryonic cells differences in early embryonic cells determine an organism’s development.determine an organism’s development.

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There are some important events that There are some important events that regulate animal development:regulate animal development:

1. Fertilization1. Fertilization2. Cleavage2. Cleavage3. Gastrulation3. Gastrulation4. Organogenesis4. Organogenesis

There are some important events that There are some important events that regulate animal development:regulate animal development:

1. Fertilization1. Fertilization2. Cleavage2. Cleavage3. Gastrulation3. Gastrulation4. Organogenesis4. Organogenesis

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1. Fertilization1. Fertilization

Fertilization is when an egg and a Fertilization is when an egg and a sperm unite forming a zygote.sperm unite forming a zygote.

The main function of fertilization is to The main function of fertilization is to produce a diploid egg. produce a diploid egg.

Egg activation occurs when the sperm Egg activation occurs when the sperm contacts the egg’s surface and initiates contacts the egg’s surface and initiates metabolic reactions that trigger the metabolic reactions that trigger the onset of embryonic development.onset of embryonic development.

Fertilization is when an egg and a Fertilization is when an egg and a sperm unite forming a zygote.sperm unite forming a zygote.

The main function of fertilization is to The main function of fertilization is to produce a diploid egg. produce a diploid egg.

Egg activation occurs when the sperm Egg activation occurs when the sperm contacts the egg’s surface and initiates contacts the egg’s surface and initiates metabolic reactions that trigger the metabolic reactions that trigger the onset of embryonic development.onset of embryonic development.

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In general, when eggs meet sperm, an In general, when eggs meet sperm, an acrosomal reaction is triggered.acrosomal reaction is triggered.

In general, when eggs meet sperm, an In general, when eggs meet sperm, an acrosomal reaction is triggered.acrosomal reaction is triggered.

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1. Fertilization1. FertilizationThe process begins when a vesicle at The process begins when a vesicle at

the tip of the sperm called the acrosome the tip of the sperm called the acrosome discharges hydrolytic enzymes.discharges hydrolytic enzymes.

The process begins when a vesicle at The process begins when a vesicle at the tip of the sperm called the acrosome the tip of the sperm called the acrosome discharges hydrolytic enzymes.discharges hydrolytic enzymes.

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1. Fertilization1. Fertilization These enzymes dissolve the egg’s jelly coat These enzymes dissolve the egg’s jelly coat

enabling the acrosomal process to penetrate enabling the acrosomal process to penetrate the it and attach to the egg’s surface.the it and attach to the egg’s surface.

These enzymes dissolve the egg’s jelly coat These enzymes dissolve the egg’s jelly coat enabling the acrosomal process to penetrate enabling the acrosomal process to penetrate the it and attach to the egg’s surface.the it and attach to the egg’s surface.

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1. Fertilization1. FertilizationThe sperm binding receptors on the The sperm binding receptors on the

egg’s surface are attached to the egg’s surface are attached to the vitelline layer. vitelline layer.

The sperm binding receptors on the The sperm binding receptors on the egg’s surface are attached to the egg’s surface are attached to the vitelline layer. vitelline layer.

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1. Fertilization1. Fertilization This recognition of the egg’s surface receptors to This recognition of the egg’s surface receptors to

sperm is what ensures only sperm from the sperm is what ensures only sperm from the same species can penetrate the egg.same species can penetrate the egg.

This recognition of the egg’s surface receptors to This recognition of the egg’s surface receptors to sperm is what ensures only sperm from the sperm is what ensures only sperm from the same species can penetrate the egg.same species can penetrate the egg.

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1. Fertilization1. FertilizationThe binding of the sperm membrane to The binding of the sperm membrane to

the membrane of the egg changes the the membrane of the egg changes the state of the ion channels of the egg.state of the ion channels of the egg.

The binding of the sperm membrane to The binding of the sperm membrane to the membrane of the egg changes the the membrane of the egg changes the state of the ion channels of the egg.state of the ion channels of the egg.

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Fast Block to PolyspermyFast Block to Polyspermy Within 1-3 seconds, depolarization occurs where NaWithin 1-3 seconds, depolarization occurs where Na++

ions rush into the egg, and is known as the fast block ions rush into the egg, and is known as the fast block to polyspermy. It prevents multiple sperm from to polyspermy. It prevents multiple sperm from entering the egg.entering the egg.

Within 1-3 seconds, depolarization occurs where NaWithin 1-3 seconds, depolarization occurs where Na++ ions rush into the egg, and is known as the fast block ions rush into the egg, and is known as the fast block to polyspermy. It prevents multiple sperm from to polyspermy. It prevents multiple sperm from entering the egg.entering the egg.

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Fast Block to PolyspermyFast Block to PolyspermyThe fast block to polyspermy is short-The fast block to polyspermy is short-

lived and the membrane polarization lived and the membrane polarization only lasts about one minute.only lasts about one minute.

The fast block to polyspermy is short-The fast block to polyspermy is short-lived and the membrane polarization lived and the membrane polarization only lasts about one minute.only lasts about one minute.

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Slow Block to PolyspermySlow Block to Polyspermy The fusion of the sperm and egg also triggers The fusion of the sperm and egg also triggers

a series of changes in the egg that are more a series of changes in the egg that are more long-lived.long-lived.

Sperm binding activates a signal transduction Sperm binding activates a signal transduction pathway which causes calcium ions to be pathway which causes calcium ions to be released from the egg’s ER into the cytosol.released from the egg’s ER into the cytosol.

The fusion of the sperm and egg also triggers The fusion of the sperm and egg also triggers a series of changes in the egg that are more a series of changes in the egg that are more long-lived.long-lived.

Sperm binding activates a signal transduction Sperm binding activates a signal transduction pathway which causes calcium ions to be pathway which causes calcium ions to be released from the egg’s ER into the cytosol.released from the egg’s ER into the cytosol.

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Slow Block to PolyspermySlow Block to Polyspermy

Release of CaRelease of Ca2+2+ from the ER occurs 1st from the ER occurs 1st at the site of sperm entry and moves at the site of sperm entry and moves like a wave over the surface of the egg.like a wave over the surface of the egg.

Release of CaRelease of Ca2+2+ from the ER occurs 1st from the ER occurs 1st at the site of sperm entry and moves at the site of sperm entry and moves like a wave over the surface of the egg.like a wave over the surface of the egg.

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The high concentration of calcium initiates the The high concentration of calcium initiates the cortical reaction.cortical reaction.

The reaction triggers the fusion of the egg’s The reaction triggers the fusion of the egg’s plasma membrane with numerous vesicles plasma membrane with numerous vesicles lying just beneath the membrane.lying just beneath the membrane.

The high concentration of calcium initiates the The high concentration of calcium initiates the cortical reaction.cortical reaction.

The reaction triggers the fusion of the egg’s The reaction triggers the fusion of the egg’s plasma membrane with numerous vesicles plasma membrane with numerous vesicles lying just beneath the membrane.lying just beneath the membrane.

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The contents of these vesicles enter the The contents of these vesicles enter the previtelline space.previtelline space.

Enzymes in these contents degrade the Enzymes in these contents degrade the proteins holding the vitelline layer to the proteins holding the vitelline layer to the plasma membrane.plasma membrane.

The contents of these vesicles enter the The contents of these vesicles enter the previtelline space.previtelline space.

Enzymes in these contents degrade the Enzymes in these contents degrade the proteins holding the vitelline layer to the proteins holding the vitelline layer to the plasma membrane.plasma membrane.

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These changes transform the vitelline These changes transform the vitelline layer into the fertilization envelope.layer into the fertilization envelope.

No more sperm can enter the egg at No more sperm can enter the egg at this time.this time.

These changes transform the vitelline These changes transform the vitelline layer into the fertilization envelope.layer into the fertilization envelope.

No more sperm can enter the egg at No more sperm can enter the egg at this time.this time.

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This is referred to as the slow block to This is referred to as the slow block to polyspermy.polyspermy.

The sharp rise in CaThe sharp rise in Ca2+2+ also increases also increases the metabolism of the egg.the metabolism of the egg.

This is referred to as the slow block to This is referred to as the slow block to polyspermy.polyspermy.

The sharp rise in CaThe sharp rise in Ca2+2+ also increases also increases the metabolism of the egg.the metabolism of the egg.

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After about 20 minutes, the egg nucleus After about 20 minutes, the egg nucleus fuses with the sperm nucleus creating a fuses with the sperm nucleus creating a diploid zygote.diploid zygote.

Fertilization has many common features Fertilization has many common features among species and many differences. among species and many differences. These differences are mainly with timing These differences are mainly with timing and various stages of meiosis.and various stages of meiosis.

After about 20 minutes, the egg nucleus After about 20 minutes, the egg nucleus fuses with the sperm nucleus creating a fuses with the sperm nucleus creating a diploid zygote.diploid zygote.

Fertilization has many common features Fertilization has many common features among species and many differences. among species and many differences. These differences are mainly with timing These differences are mainly with timing and various stages of meiosis.and various stages of meiosis.

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1. Fertilization--Sperm Activation1. Fertilization--Sperm Activation In mammals, secretions in the female In mammals, secretions in the female

reproductive tract to help to activate sperm. reproductive tract to help to activate sperm. Additionally, the mammalian egg is cloaked Additionally, the mammalian egg is cloaked

by follicle cells through which the sperm must by follicle cells through which the sperm must penetrate before reaching the zona pellucida.penetrate before reaching the zona pellucida.

In mammals, secretions in the female In mammals, secretions in the female reproductive tract to help to activate sperm. reproductive tract to help to activate sperm.

Additionally, the mammalian egg is cloaked Additionally, the mammalian egg is cloaked by follicle cells through which the sperm must by follicle cells through which the sperm must penetrate before reaching the zona pellucida.penetrate before reaching the zona pellucida.

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1. Fertilization--Sperm Activation1. Fertilization--Sperm Activation The zona pellucida is the The zona pellucida is the

external matrix of the egg external matrix of the egg and functions as a sperm and functions as a sperm receptor. receptor.

When sperm binds to When sperm binds to this, it induces many of this, it induces many of the same reactions as the same reactions as seen in the sea urchin.seen in the sea urchin.

One difference is that One difference is that there is no fast block to there is no fast block to polyspermy in mammals.polyspermy in mammals.

The zona pellucida is the The zona pellucida is the external matrix of the egg external matrix of the egg and functions as a sperm and functions as a sperm receptor. receptor.

When sperm binds to When sperm binds to this, it induces many of this, it induces many of the same reactions as the same reactions as seen in the sea urchin.seen in the sea urchin.

One difference is that One difference is that there is no fast block to there is no fast block to polyspermy in mammals.polyspermy in mammals.

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1. Fertilization--Sperm Activation1. Fertilization--Sperm Activation

After the egg and sperm membranes After the egg and sperm membranes fuse the whole sperm is taken into the fuse the whole sperm is taken into the egg.egg.

The egg lacks a centrosome which the The egg lacks a centrosome which the sperm has.sperm has.

The centrosome will duplicate and The centrosome will duplicate and assist in the creation of the mitotic assist in the creation of the mitotic spindle which will be used for the first spindle which will be used for the first cell division.cell division.

After the egg and sperm membranes After the egg and sperm membranes fuse the whole sperm is taken into the fuse the whole sperm is taken into the egg.egg.

The egg lacks a centrosome which the The egg lacks a centrosome which the sperm has.sperm has.

The centrosome will duplicate and The centrosome will duplicate and assist in the creation of the mitotic assist in the creation of the mitotic spindle which will be used for the first spindle which will be used for the first cell division.cell division.

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1. Fertilization--Sperm Activation1. Fertilization--Sperm Activation

In mammals, the nuclei do not In mammals, the nuclei do not immediately fuse. Instead, the 2 sets of immediately fuse. Instead, the 2 sets of c-somes share a common spindle c-somes share a common spindle apparatus during the 1st mitotic division.apparatus during the 1st mitotic division.

Only after the first division, as diploid Only after the first division, as diploid nuclei form in the 2 daughter cells, do nuclei form in the 2 daughter cells, do the chromosomes from the 2 parents the chromosomes from the 2 parents come together in a common nucleus. come together in a common nucleus.

In mammals, the nuclei do not In mammals, the nuclei do not immediately fuse. Instead, the 2 sets of immediately fuse. Instead, the 2 sets of c-somes share a common spindle c-somes share a common spindle apparatus during the 1st mitotic division.apparatus during the 1st mitotic division.

Only after the first division, as diploid Only after the first division, as diploid nuclei form in the 2 daughter cells, do nuclei form in the 2 daughter cells, do the chromosomes from the 2 parents the chromosomes from the 2 parents come together in a common nucleus. come together in a common nucleus.

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Fertilization is quite slow in mammals.Fertilization is quite slow in mammals.Once fertilization is complete, rapid cell Once fertilization is complete, rapid cell

division ensues and the cells proceed division ensues and the cells proceed through the M and S phases of the cell through the M and S phases of the cell cycle virtually skipping G1 and G2.cycle virtually skipping G1 and G2.

Fertilization is quite slow in mammals.Fertilization is quite slow in mammals.Once fertilization is complete, rapid cell Once fertilization is complete, rapid cell

division ensues and the cells proceed division ensues and the cells proceed through the M and S phases of the cell through the M and S phases of the cell cycle virtually skipping G1 and G2.cycle virtually skipping G1 and G2.

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Thus, the embryo doesn’t enlarge Thus, the embryo doesn’t enlarge much. Rather, it becomes an aggregate much. Rather, it becomes an aggregate of blastomeres called a blastocyst of blastomeres called a blastocyst (blastula).(blastula).

Thus, the embryo doesn’t enlarge Thus, the embryo doesn’t enlarge much. Rather, it becomes an aggregate much. Rather, it becomes an aggregate of blastomeres called a blastocyst of blastomeres called a blastocyst (blastula).(blastula).

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Copyright ©2005 Pearson Education, Inc. Publishing as Pearson Benjamin Cummings. All rights reserved.

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2. Cleavage2. Cleavage

The color of the frog The color of the frog egg cells allows for egg cells allows for easy following of cells easy following of cells during development.during development.

Animal hemisphere is Animal hemisphere is deep gray due to deep gray due to melanin.melanin.

The vegetal pole is The vegetal pole is yellow due to lack of yellow due to lack of melanin.melanin.

The color of the frog The color of the frog egg cells allows for egg cells allows for easy following of cells easy following of cells during development.during development.

Animal hemisphere is Animal hemisphere is deep gray due to deep gray due to melanin.melanin.

The vegetal pole is The vegetal pole is yellow due to lack of yellow due to lack of melanin.melanin.

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The first 5 to 7 divisions produce what is The first 5 to 7 divisions produce what is called the morula. called the morula.

Within the morula a fluid filled cavity called a Within the morula a fluid filled cavity called a blastocoel forms. When fully formed, the blastocoel forms. When fully formed, the aggregate of cells is now called blastula.aggregate of cells is now called blastula.

The first 5 to 7 divisions produce what is The first 5 to 7 divisions produce what is called the morula. called the morula.

Within the morula a fluid filled cavity called a Within the morula a fluid filled cavity called a blastocoel forms. When fully formed, the blastocoel forms. When fully formed, the aggregate of cells is now called blastula.aggregate of cells is now called blastula.

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Many animals, with the exception of Many animals, with the exception of possibly mammals, have zygotes with a possibly mammals, have zygotes with a definite polarity that determines the definite polarity that determines the pattern of cleavage.pattern of cleavage.

Many animals, with the exception of Many animals, with the exception of possibly mammals, have zygotes with a possibly mammals, have zygotes with a definite polarity that determines the definite polarity that determines the pattern of cleavage.pattern of cleavage.

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2. Cleavage2. Cleavage In classic examples In classic examples

such as the frog, the such as the frog, the distribution of yolk in the distribution of yolk in the egg determines egg determines cleavage patterns.cleavage patterns.

The vegetal pole The vegetal pole contains a large amount contains a large amount of yolk, and cleavage of yolk, and cleavage through this is slow.through this is slow.

The animal pole The animal pole contains very little yolk contains very little yolk and cleavage occurs and cleavage occurs quickly through it. quickly through it.

In classic examples In classic examples such as the frog, the such as the frog, the distribution of yolk in the distribution of yolk in the egg determines egg determines cleavage patterns.cleavage patterns.

The vegetal pole The vegetal pole contains a large amount contains a large amount of yolk, and cleavage of yolk, and cleavage through this is slow.through this is slow.

The animal pole The animal pole contains very little yolk contains very little yolk and cleavage occurs and cleavage occurs quickly through it. quickly through it.

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2. Cleavage--3 Body Axes2. Cleavage--3 Body Axes

The 3 body axes are The 3 body axes are established early on established early on in development. in development.

1. Dorsal/ventral1. Dorsal/ventral2. Right/left2. Right/left3. Anterior/posterior3. Anterior/posterior

The 3 body axes are The 3 body axes are established early on established early on in development. in development.

1. Dorsal/ventral1. Dorsal/ventral2. Right/left2. Right/left3. Anterior/posterior3. Anterior/posterior

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2. Cleavage2. CleavageUsing the frog as an Using the frog as an

example, fusion of example, fusion of the sperm and egg the sperm and egg initiates a body axis.initiates a body axis.

At this point, the At this point, the animal pole will animal pole will move toward the move toward the vegetal pole passing vegetal pole passing through the site of through the site of sperm entry.sperm entry.

Using the frog as an Using the frog as an example, fusion of example, fusion of the sperm and egg the sperm and egg initiates a body axis.initiates a body axis.

At this point, the At this point, the animal pole will animal pole will move toward the move toward the vegetal pole passing vegetal pole passing through the site of through the site of sperm entry.sperm entry.




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As a result of the As a result of the cortical rotation, a cortical rotation, a light gray region light gray region known as the gray known as the gray crescent forms in crescent forms in some species and some species and the dorsal/ventral the dorsal/ventral axis is formed in axis is formed in the zygote.the zygote.

As a result of the As a result of the cortical rotation, a cortical rotation, a light gray region light gray region known as the gray known as the gray crescent forms in crescent forms in some species and some species and the dorsal/ventral the dorsal/ventral axis is formed in axis is formed in the zygote.the zygote.




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2. Cleavage2. CleavageThis light gray This light gray

region forms the region forms the dorsal side of the dorsal side of the embryo.embryo.

In frogs (animals In frogs (animals with a thick vegetal with a thick vegetal pole), the pole), the blastocoel, is blastocoel, is located in the located in the animal pole animal pole because the yolk because the yolk isn’t as thick.isn’t as thick.

This light gray This light gray region forms the region forms the dorsal side of the dorsal side of the embryo.embryo.

In frogs (animals In frogs (animals with a thick vegetal with a thick vegetal pole), the pole), the blastocoel, is blastocoel, is located in the located in the animal pole animal pole because the yolk because the yolk isn’t as thick.isn’t as thick.




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2. Cleavage2. Cleavage Yolk is very Yolk is very

plentiful in many plentiful in many animals such as a animals such as a bird.bird.

In this example, the In this example, the yolk is actually an yolk is actually an egg cell swollen egg cell swollen with yolk nutrients. with yolk nutrients. A small white disk A small white disk of actual cytoplasm of actual cytoplasm is located on the is located on the animal pole.animal pole.

Yolk is very Yolk is very plentiful in many plentiful in many animals such as a animals such as a bird.bird.

In this example, the In this example, the yolk is actually an yolk is actually an egg cell swollen egg cell swollen with yolk nutrients. with yolk nutrients. A small white disk A small white disk of actual cytoplasm of actual cytoplasm is located on the is located on the animal pole.animal pole.

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The entire cell The entire cell is surrounded is surrounded by a protein by a protein rich solution of rich solution of egg white egg white which provides which provides additional additional nutrients to the nutrients to the growing growing embryo.embryo.

The entire cell The entire cell is surrounded is surrounded by a protein by a protein rich solution of rich solution of egg white egg white which provides which provides additional additional nutrients to the nutrients to the growing growing embryo.embryo.

YolkChalaza Disk of Cytoplasm

Albumen

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Cleavage is Cleavage is restricted to the restricted to the small disk of small disk of yolk free yolk free cytoplasm.cytoplasm.

Cleavage can’t Cleavage can’t proceed through proceed through the dense yolk.the dense yolk.

Cleavage is Cleavage is restricted to the restricted to the small disk of small disk of yolk free yolk free cytoplasm.cytoplasm.

Cleavage can’t Cleavage can’t proceed through proceed through the dense yolk.the dense yolk.

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Incomplete division of the Incomplete division of the yolk rich egg is known as yolk rich egg is known as meroblastic cleavage.meroblastic cleavage.

In contrast, holoblastic In contrast, holoblastic cleavage results in cleavage results in complete division of the complete division of the egg that lacks a lot of egg that lacks a lot of yolk, (or a moderate yolk, (or a moderate amount of yolk).amount of yolk).

Incomplete division of the Incomplete division of the yolk rich egg is known as yolk rich egg is known as meroblastic cleavage.meroblastic cleavage.

In contrast, holoblastic In contrast, holoblastic cleavage results in cleavage results in complete division of the complete division of the egg that lacks a lot of egg that lacks a lot of yolk, (or a moderate yolk, (or a moderate amount of yolk).amount of yolk).





http://scienceblogs.com/pharyngula/2006/07/the_evolution_of_deuterostome.php

http://scienceblogs.com/pharyngula/2006/07/the_evolution_of_deuterostome.php

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2. Cleavage2. CleavageThe cleaving cells on the top of the yolk The cleaving cells on the top of the yolk

of a bird egg produce a cap of cells of a bird egg produce a cap of cells called the blastoderm.called the blastoderm.

The blastoderm then rests on the yolk The blastoderm then rests on the yolk and divides into 2 layers called the and divides into 2 layers called the epiblast and the hypoblast.epiblast and the hypoblast.

The cleaving cells on the top of the yolk The cleaving cells on the top of the yolk of a bird egg produce a cap of cells of a bird egg produce a cap of cells called the blastoderm.called the blastoderm.

The blastoderm then rests on the yolk The blastoderm then rests on the yolk and divides into 2 layers called the and divides into 2 layers called the epiblast and the hypoblast.epiblast and the hypoblast.




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The cavity between them is called the The cavity between them is called the blastocoel.blastocoel.

This is the equivalent of the blastula This is the equivalent of the blastula stage of the frog/sea urchin.stage of the frog/sea urchin.

The cavity between them is called the The cavity between them is called the blastocoel.blastocoel.

This is the equivalent of the blastula This is the equivalent of the blastula stage of the frog/sea urchin.stage of the frog/sea urchin.




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3. Gastrulation3. GastrulationGastrulation is the rearrangement of Gastrulation is the rearrangement of

cells of the blastula to form a 3 layered cells of the blastula to form a 3 layered embryo with a primitive gut.embryo with a primitive gut.

Gastrulation is the rearrangement of Gastrulation is the rearrangement of cells of the blastula to form a 3 layered cells of the blastula to form a 3 layered embryo with a primitive gut.embryo with a primitive gut.

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3. Gastrulation3. Gastrulation

Gastrulation differs between animal Gastrulation differs between animal groups, but it shares some general groups, but it shares some general characteristics:characteristics: A. Changes in cell motility.A. Changes in cell motility. B. Changes in cell shape.B. Changes in cell shape. C. Changes in cellular adhesion.C. Changes in cellular adhesion.

Gastrulation differs between animal Gastrulation differs between animal groups, but it shares some general groups, but it shares some general characteristics:characteristics: A. Changes in cell motility.A. Changes in cell motility. B. Changes in cell shape.B. Changes in cell shape. C. Changes in cellular adhesion.C. Changes in cellular adhesion.

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3. Gastrulation3. Gastrulation The result is that some cells The result is that some cells

at the surface of the blastula at the surface of the blastula move inward establishing 3 move inward establishing 3 cell layers.cell layers.

The 3 layered embryo is The 3 layered embryo is called the gastrula.called the gastrula.

The 3 layers are given the The 3 layers are given the term embryonic germ layers term embryonic germ layers and consist of:and consist of: 11. Endoderm--lines digestive . Endoderm--lines digestive

tract.tract. 2. Mesoderm--partially fills the 2. Mesoderm--partially fills the

space between endoderm and space between endoderm and ectoderm.ectoderm.

3. Ectoderm--which forms the 3. Ectoderm--which forms the outer layer of the gastrula.outer layer of the gastrula.

The result is that some cells The result is that some cells at the surface of the blastula at the surface of the blastula move inward establishing 3 move inward establishing 3 cell layers.cell layers.

The 3 layered embryo is The 3 layered embryo is called the gastrula.called the gastrula.

The 3 layers are given the The 3 layers are given the term embryonic germ layers term embryonic germ layers and consist of:and consist of: 11. Endoderm--lines digestive . Endoderm--lines digestive

tract.tract. 2. Mesoderm--partially fills the 2. Mesoderm--partially fills the

space between endoderm and space between endoderm and ectoderm.ectoderm.

3. Ectoderm--which forms the 3. Ectoderm--which forms the outer layer of the gastrula.outer layer of the gastrula.

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3. Gastrulation--Sea Urchin3. Gastrulation--Sea Urchin These 3 layers will form all These 3 layers will form all

cell layers and tissues in cell layers and tissues in the adult animal.the adult animal.

In the sea urchin, the In the sea urchin, the blastula consists of a single blastula consists of a single layer of cells enclosing a layer of cells enclosing a blastocoel.blastocoel.

Gastrulation begins at the Gastrulation begins at the vegetal pole.vegetal pole.

Here, migratory cells called Here, migratory cells called mesenchyme cells enter mesenchyme cells enter the blastocoel.the blastocoel.

These 3 layers will form all These 3 layers will form all cell layers and tissues in cell layers and tissues in the adult animal.the adult animal.

In the sea urchin, the In the sea urchin, the blastula consists of a single blastula consists of a single layer of cells enclosing a layer of cells enclosing a blastocoel.blastocoel.

Gastrulation begins at the Gastrulation begins at the vegetal pole.vegetal pole.

Here, migratory cells called Here, migratory cells called mesenchyme cells enter mesenchyme cells enter the blastocoel.the blastocoel.

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3. Gastrulation--Sea Urchin3. Gastrulation--Sea Urchin The cells which remain The cells which remain

form the vegetal plate form the vegetal plate which eventually buckles which eventually buckles inward by a process inward by a process called invagination.called invagination.

Invagination proceeds Invagination proceeds forming the archenteron forming the archenteron (primitive gut).(primitive gut).

The open end of the The open end of the archenteron will become archenteron will become the anus, it is called the the anus, it is called the blastopore.blastopore.

The cells which remain The cells which remain form the vegetal plate form the vegetal plate which eventually buckles which eventually buckles inward by a process inward by a process called invagination.called invagination.

Invagination proceeds Invagination proceeds forming the archenteron forming the archenteron (primitive gut).(primitive gut).

The open end of the The open end of the archenteron will become archenteron will become the anus, it is called the the anus, it is called the blastopore.blastopore.

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3. Gastrulation--Sea Urchin3. Gastrulation--Sea UrchinThe second opening The second opening

forms as the archenteron forms as the archenteron touches the inside of the touches the inside of the ectoderm on the other ectoderm on the other side. This is the mouth side. This is the mouth (in deuterostomes).(in deuterostomes).

A rudimentary digestive A rudimentary digestive tube is now formed.tube is now formed.

The second opening The second opening forms as the archenteron forms as the archenteron touches the inside of the touches the inside of the ectoderm on the other ectoderm on the other side. This is the mouth side. This is the mouth (in deuterostomes).(in deuterostomes).

A rudimentary digestive A rudimentary digestive tube is now formed.tube is now formed.



http://biology.kenyon.edu/courses/biol114/Chap14/PMC_SEM.gif

Blastocoel

Vegetal Plate

Mesenchyme Cells

Ectoderm

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3. Gastrulation--Frog3. Gastrulation--Frog In the frog, gastrulation In the frog, gastrulation

also produces a 3 layered also produces a 3 layered embryo with an embryo with an archenteron.archenteron.

Gastrulation is more Gastrulation is more complex due to the yolk complex due to the yolk content of the cells, and content of the cells, and the fact that the wall of the the fact that the wall of the blastula is more than 1 blastula is more than 1 cell-layer thick.cell-layer thick.

Gastrulation begins on the Gastrulation begins on the dorsal side of the blastula dorsal side of the blastula in a line along the region in a line along the region of the gray crescent.of the gray crescent.

In the frog, gastrulation In the frog, gastrulation also produces a 3 layered also produces a 3 layered embryo with an embryo with an archenteron.archenteron.

Gastrulation is more Gastrulation is more complex due to the yolk complex due to the yolk content of the cells, and content of the cells, and the fact that the wall of the the fact that the wall of the blastula is more than 1 blastula is more than 1 cell-layer thick.cell-layer thick.

Gastrulation begins on the Gastrulation begins on the dorsal side of the blastula dorsal side of the blastula in a line along the region in a line along the region of the gray crescent.of the gray crescent.

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3. Gastrulation--Frog3. Gastrulation--FrogThis invagination This invagination

forms the dorsal lip forms the dorsal lip which pinches inward which pinches inward around the cell.around the cell.

The cells on the The cells on the surface of the surface of the embryo continue to embryo continue to roll inward in a roll inward in a process called process called involution forming the involution forming the future endoderm and future endoderm and mesoderm.mesoderm.

This invagination This invagination forms the dorsal lip forms the dorsal lip which pinches inward which pinches inward around the cell.around the cell.

The cells on the The cells on the surface of the surface of the embryo continue to embryo continue to roll inward in a roll inward in a process called process called involution forming the involution forming the future endoderm and future endoderm and mesoderm.mesoderm.

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3. Gastrulation--Frog3. Gastrulation--Frog Eventually, the Eventually, the

blastocoel collapses as blastocoel collapses as the archenteron replaces the archenteron replaces it. The archenteron is it. The archenteron is lined with endoderm.lined with endoderm.

As gastrulation As gastrulation completes, the completes, the blastopore encircles the blastopore encircles the yolk plug.yolk plug.

After the archenteron After the archenteron reaches the opposite reaches the opposite side of the embryo, a side of the embryo, a mouth will form.mouth will form.

Eventually, the Eventually, the blastocoel collapses as blastocoel collapses as the archenteron replaces the archenteron replaces it. The archenteron is it. The archenteron is lined with endoderm.lined with endoderm.

As gastrulation As gastrulation completes, the completes, the blastopore encircles the blastopore encircles the yolk plug.yolk plug.

After the archenteron After the archenteron reaches the opposite reaches the opposite side of the embryo, a side of the embryo, a mouth will form.mouth will form.

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3. Gastrulation--Chick3. Gastrulation--ChickThe chick’s gastrulation is similar to that of The chick’s gastrulation is similar to that of

a frog except the inward movement of cells a frog except the inward movement of cells during gastrulation is affected by the yolk.during gastrulation is affected by the yolk.

The chick’s gastrulation is similar to that of The chick’s gastrulation is similar to that of a frog except the inward movement of cells a frog except the inward movement of cells during gastrulation is affected by the yolk.during gastrulation is affected by the yolk.

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3. Gastrulation--Chick3. Gastrulation--ChickCleavage in the chick results in a Cleavage in the chick results in a

blastoderm with an epiblast and a blastoderm with an epiblast and a hypoblast.hypoblast.

Cleavage in the chick results in a Cleavage in the chick results in a blastoderm with an epiblast and a blastoderm with an epiblast and a hypoblast.hypoblast.

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3. Gastrulation--Chick3. Gastrulation--Chick All cells that form the embryo will come from the epiblast.All cells that form the embryo will come from the epiblast. During gastrulation, some of the epiblast cells move toward During gastrulation, some of the epiblast cells move toward

the blastoderm’s midline producing a thickening called the the blastoderm’s midline producing a thickening called the primitive streak.primitive streak.

All cells that form the embryo will come from the epiblast.All cells that form the embryo will come from the epiblast. During gastrulation, some of the epiblast cells move toward During gastrulation, some of the epiblast cells move toward

the blastoderm’s midline producing a thickening called the the blastoderm’s midline producing a thickening called the primitive streak.primitive streak.

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3. Gastrulation--Chick3. Gastrulation--ChickThe primitive streak will The primitive streak will

form the bird’s form the bird’s anterior/posterior axis.anterior/posterior axis.

The primitive streak is The primitive streak is the functional equivalent the functional equivalent to the lip of the to the lip of the blastopore in the frog, blastopore in the frog, but structures are but structures are aligned differently.aligned differently.

Inward moving cells Inward moving cells displace hypoblast cells displace hypoblast cells and form endoderm.and form endoderm.

The primitive streak will The primitive streak will form the bird’s form the bird’s anterior/posterior axis.anterior/posterior axis.

The primitive streak is The primitive streak is the functional equivalent the functional equivalent to the lip of the to the lip of the blastopore in the frog, blastopore in the frog, but structures are but structures are aligned differently.aligned differently.

Inward moving cells Inward moving cells displace hypoblast cells displace hypoblast cells and form endoderm.and form endoderm.

Scott F. Gilbert Developmental Biology

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3. Gastrulation--Chick3. Gastrulation--Chick Other epiblast cells move laterally into the Other epiblast cells move laterally into the

blastocoel and form mesoderm.blastocoel and form mesoderm. Epiblast cells remaining on the surface form Epiblast cells remaining on the surface form

ectoderm.ectoderm. The hypoblast helps direct the formation of the The hypoblast helps direct the formation of the

primitive streak and forms part of the stalk that primitive streak and forms part of the stalk that keeps the yolk mass connected to the embryo.keeps the yolk mass connected to the embryo.

Other epiblast cells move laterally into the Other epiblast cells move laterally into the blastocoel and form mesoderm.blastocoel and form mesoderm.

Epiblast cells remaining on the surface form Epiblast cells remaining on the surface form ectoderm.ectoderm.

The hypoblast helps direct the formation of the The hypoblast helps direct the formation of the primitive streak and forms part of the stalk that primitive streak and forms part of the stalk that keeps the yolk mass connected to the embryo.keeps the yolk mass connected to the embryo.

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4. Organogenesis4. Organogenesis Organogenesis is the process by which parts of the 3 Organogenesis is the process by which parts of the 3

germ layers develop the rudiments of organs. germ layers develop the rudiments of organs. Organogenesis involves localized morphogenic Organogenesis involves localized morphogenic

changes in tissue and cell shape versus the large changes in tissue and cell shape versus the large scale mass movement of cells seen in gastrulation.scale mass movement of cells seen in gastrulation.

Organogenesis is the process by which parts of the 3 Organogenesis is the process by which parts of the 3 germ layers develop the rudiments of organs. germ layers develop the rudiments of organs.

Organogenesis involves localized morphogenic Organogenesis involves localized morphogenic changes in tissue and cell shape versus the large changes in tissue and cell shape versus the large scale mass movement of cells seen in gastrulation.scale mass movement of cells seen in gastrulation.

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4. Organogenesis4. Organogenesis Evidence of organogenesis is seen in the Evidence of organogenesis is seen in the

appearance of folds splits and dense appearance of folds splits and dense clustering of cells.clustering of cells.

Easy observations are made in chordates Easy observations are made in chordates when the notochord, neural tube, etc. take when the notochord, neural tube, etc. take form.form.

Evidence of organogenesis is seen in the Evidence of organogenesis is seen in the appearance of folds splits and dense appearance of folds splits and dense clustering of cells.clustering of cells.

Easy observations are made in chordates Easy observations are made in chordates when the notochord, neural tube, etc. take when the notochord, neural tube, etc. take form.form.

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4. Organogenesis4. OrganogenesisThe notochord is formed from dorsal The notochord is formed from dorsal

mesoderm which condenses just above mesoderm which condenses just above the archenteron.the archenteron.

The notochord is formed from dorsal The notochord is formed from dorsal mesoderm which condenses just above mesoderm which condenses just above the archenteron.the archenteron.

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4. Organogenesis4. Organogenesis Signals sent from the notochord to the Signals sent from the notochord to the

ectoderm cause the region of the ectoderm to ectoderm cause the region of the ectoderm to form the neural plate.form the neural plate.

The neural plate will curve inward forming the The neural plate will curve inward forming the neural tube which runs along the anterior-neural tube which runs along the anterior-posterior axis of the embryo eventually posterior axis of the embryo eventually forming the CNS.forming the CNS.

Signals sent from the notochord to the Signals sent from the notochord to the ectoderm cause the region of the ectoderm to ectoderm cause the region of the ectoderm to form the neural plate.form the neural plate.

The neural plate will curve inward forming the The neural plate will curve inward forming the neural tube which runs along the anterior-neural tube which runs along the anterior-posterior axis of the embryo eventually posterior axis of the embryo eventually forming the CNS.forming the CNS.

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4. Organogenesis4. Organogenesis In vertebrates, the In vertebrates, the

neural crest forms neural crest forms along the border along the border where the neural tube where the neural tube pinches off from the pinches off from the ectoderm.ectoderm.

Neural crest cells then Neural crest cells then migrate to various migrate to various parts of the embryo parts of the embryo giving rise to many giving rise to many structures such as structures such as peripheral nerves, peripheral nerves, teeth, skull bones, etc.teeth, skull bones, etc.

In vertebrates, the In vertebrates, the neural crest forms neural crest forms along the border along the border where the neural tube where the neural tube pinches off from the pinches off from the ectoderm.ectoderm.

Neural crest cells then Neural crest cells then migrate to various migrate to various parts of the embryo parts of the embryo giving rise to many giving rise to many structures such as structures such as peripheral nerves, peripheral nerves, teeth, skull bones, etc.teeth, skull bones, etc.

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4. Organogenesis4. OrganogenesisLateral to the Lateral to the

notochord are notochord are condensations of condensations of mesodermal cells mesodermal cells arranged in the block arranged in the block called somites.called somites.

The somites give rise The somites give rise to cells that migrate to to cells that migrate to new locations forming new locations forming vertebrae and vertebrae and muscles.muscles.

Lateral to the Lateral to the notochord are notochord are condensations of condensations of mesodermal cells mesodermal cells arranged in the block arranged in the block called somites.called somites.

The somites give rise The somites give rise to cells that migrate to to cells that migrate to new locations forming new locations forming vertebrae and vertebrae and muscles.muscles.

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DevelopmentDevelopment

All vertebrates require an aqueous All vertebrates require an aqueous environment to grow and develop.environment to grow and develop.

The evolution of structures that allow The evolution of structures that allow this to happen have occurred and are this to happen have occurred and are the shelled egg and uterus. These the shelled egg and uterus. These structures protect the embryo with an structures protect the embryo with an amnion which is a fluid filled sac.amnion which is a fluid filled sac.

All vertebrates require an aqueous All vertebrates require an aqueous environment to grow and develop.environment to grow and develop.

The evolution of structures that allow The evolution of structures that allow this to happen have occurred and are this to happen have occurred and are the shelled egg and uterus. These the shelled egg and uterus. These structures protect the embryo with an structures protect the embryo with an amnion which is a fluid filled sac.amnion which is a fluid filled sac.

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Extraembryonic MembranesExtraembryonic Membranes

The development of mammals, birds, The development of mammals, birds, and reptiles includes the formation of 4 and reptiles includes the formation of 4 extraembryonic membranes.extraembryonic membranes.

These membranes include:These membranes include: Yolk sacYolk sac ChorionChorion AllantoisAllantois AmnionAmnion

The development of mammals, birds, The development of mammals, birds, and reptiles includes the formation of 4 and reptiles includes the formation of 4 extraembryonic membranes.extraembryonic membranes.

These membranes include:These membranes include: Yolk sacYolk sac ChorionChorion AllantoisAllantois AmnionAmnion

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Extraembryonic MembranesExtraembryonic MembranesThe yolk sac covers the yolk and The yolk sac covers the yolk and

develops blood vessels that transplant develops blood vessels that transplant nutrients from the yolk to the embryo.nutrients from the yolk to the embryo.

The yolk sac covers the yolk and The yolk sac covers the yolk and develops blood vessels that transplant develops blood vessels that transplant nutrients from the yolk to the embryo.nutrients from the yolk to the embryo.

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Extraembryonic MembranesExtraembryonic MembranesThe chorion is involved in gas exchange The chorion is involved in gas exchange

with the surroundings.with the surroundings.The chorion is involved in gas exchange The chorion is involved in gas exchange

with the surroundings.with the surroundings.

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Extraembryonic MembranesExtraembryonic Membranes The allantois is a disposable sac for metabolic The allantois is a disposable sac for metabolic

wastes produced by the developing embryo. wastes produced by the developing embryo. It also functions with the chorion in respiration.It also functions with the chorion in respiration.

The allantois is a disposable sac for metabolic The allantois is a disposable sac for metabolic wastes produced by the developing embryo. wastes produced by the developing embryo. It also functions with the chorion in respiration.It also functions with the chorion in respiration.

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Extraembryonic MembranesExtraembryonic MembranesThe amnion protects the embryo in a The amnion protects the embryo in a

fluid filled cavity.fluid filled cavity.The amnion protects the embryo in a The amnion protects the embryo in a

fluid filled cavity.fluid filled cavity.

Travismulthaupt.com Chapter 47 Animal Development.

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