Molecular and Organismal Development

Chapter 21: pp 411-429

Chapter 47: pp 992-1008

Topics in Development• 1. totipotency: development depends on selective expression of

the whole genome present in every cell.  

• 2. blastula to gastrula: comparative analysis yields insights into the general nature of development

• 3. the three fundamental processes:

– cell division (differential rates of division are critical, programmed cell death is significant)

– cell differentiation (changes in integration and shape are critical; targeting cells with signals is a critical part of the process)

– morphogenesis of tissues and organs (includes defining the individual’s polarities, dividing the organism into segments, and – in animals -- migration of cells in tissue origin)

Figure 21.2 Some key stages of development in animals and plants

Figure 21.5 Test-tube cloning of carrots

Figure 21.8 Working with stem cells

Topics in Development• 1. totipotency: development depends on selective expression of

the whole genome present in every cell.  

• 2. blastula to gastrula: comparative analysis yields insights into the general nature of development

• 3. the three fundamental processes:

– cell division (differential rates of division are critical, programmed cell death is significant)

– cell differentiation (changes in integration and shape are critical; targeting cells with signals is a critical part of the process)

– morphogenesis of tissues and organs (includes defining the individual’s polarities, dividing the organism into segments, and – in animals -- migration of cells in tissue origin)

Figure 47.6 Cleavage in an echinoderm (sea urchin) embryo

Figure 47.9 Sea urchin gastrulation (Layer 3)

Figure 47.8x Cleavage in a frog embryo

Figure 47.8d Cross section of a frog blastula

Figure 47.10 Gastrulation in a frog embryo

Figure 47.12 Gastrulation in a

frog embryo

Figure 47.12 Cleavage, gastrulation, and early organogenesis in a chick embryo

The cells in the three germ layers have defined fates in the adult:

Topics in Development• 1. totipotency: development depends on selective expression of

the whole genome present in every cell.  

• 2. blastula to gastrula: comparative analysis yields insights into the general nature of development

• 3. the three fundamental processes:

– cell division (differential rates of division are critical, programmed cell death is significant)

– cell differentiation (changes in integration and shape are critical; targeting cells with signals is a critical part of the process)

– morphogenesis of tissues and organs (includes defining the individual’s polarities, dividing the organism into segments, and – in animals -- migration of cells in tissue origin)

Figure 21.4 Cell lineage in C. elegans

C. elegans cell targeting

C. elegans cell targeting

Figure 47.14 Organogenesis in a frog embryo

Figure 47.16 Change in cellular shape during morphogenesis

Apoptosis in development

Topics in Development

4. Homeotic genes a. the determination of appendage identity on fruitfly segmentsb. the evolution of form in segmented animals

4. Morphogenesis in Plants5. Organ identity genes in flower development

Figure 21.11 Key developmental events in the life cycle of Drosophila

Figure 21.12 The effect of the bicoid gene, a maternal effect (egg-polarity) gene Drosophila

Figure 21.13 Segmentation genes in Drosophila

Figure 21.13  Homeotic mutations and abnormal pattern formation in Drosophila

The homeodomain - 60 amino acids of the homeotic gene product that remain very similar in all proteins made by homeotic genes.

Homeotic genes:the DNA sequence of the gene (blue) contains a 180 bp sequence—the homeobox—(red) that

is highly conserved.

Figure 17.7 The initiation of transcription at a eukaryotic promoter

control of transcription in C.elegans lin-3

|tctctccctattcaatgcacctgtgtattttatgctggttttttcttgtgaccctgaaaactgtacacacaggtgttcttaccaatgtctcaggcatttttggaaaagtaatattaagaaaattatacatattttcttgaatacgaaaaatttaaATGTTCGGTAAATCGATTCCTGAACGACTTCTAGTCGCATT

T

HLH-2 binding siteNHR binding site

EXON is in uppercase letters. 

Figure 19.10 Three of the major types of DNA-binding domains in transcription factors

The homeobox is relatively constant because it has a precise job.

The homeobox is relatively constant because it has a precise job.

Figure 21.14  Homologous genes that affect pattern formation in a fruit fly and a mouse

Topics in Development

4. Homeotic genes a. the determination of appendage identity on fruitfly segmentsb. the evolution of form in segmented animals

4. Morphogenesis in Plants5. Organ identity genes in flower development

Serial Homology of the Lobster

CRUSTACEANS COMPARED - EVOLUTIONARY HOMOLOGY

CRUSTACEANS COMPARED: EVOLUTIONARY TRANSFORMATION

LOBSTERROCK CRAB

Figure 33.28 Horseshoe crabs, Limulus polyphemus

Figure 33.27 A trilobite fossil

Figure 33.x1 Insecta: beetle

Figure 32.8 Animal phylogeny based on sequencing of SSU-rRNA

lophophore

Figure 32.13x Burgess Shale fossils

Figure 32.13 A sample of some of the animals that evolved during the Cambrian explosion

Porifera and Cnidaria are prominent in the Burgess Shale

Annelid worms in the Burgess shale

Anomalocaris hunts

so are arthropods!!

Figure 26.8 The Cambrian radiation of animals

Causes of the radiation:

1. Atmospheric oxygen reaches sufficient levels.

2. Predator-prey relationships originate.

3. Homeobox genes evolve.

(Ediacaran)

525BurgessShale

PLPL PL

PE

DD

RP

Evolutionary changes in the timing of homeobox genes yield morphological change.

Artemia, the brine shrimp

Another representation of the sequence of homeotic gene expression in an arthropod.

Notice the continued prominence of Antp, Ubx, and Abd paralogs.

Timing of expression of the homeobox genes Antp, Ubx, and AbdA. Fading lines indicate weaker expression later

in development.

Number of homeobox paralogs increases in arthropods.

This illustration also shows

change in timing of gene expression.

Dm - FruitflyTc - BeetleJc - ButterflyAk - Onycho- phoran

Amino acid sequences compared for the homeotic gene Ubx

insects

arthropods

Decides six legs versus more

Topics in Development

4. Homeotic genes a. the determination of appendage identity on fruitfly segmentsb. the evolution of form in segmented animals

4. Morphogenesis in Plants5. Organ identity genes in flower development

Figure 35.13 Morphology of a winter twig

Goethe’s inspiration - the European Fan Palm at the Padua Botanical

GardenJohann Wolfgang von Goethe1749 - 1832

Padua Botanical Garden

SERIAL HOMOLOGY - GOETHE’S PALM

Figure 35.17 The terminal bud and primary growth of a shoot

Figure 21.20a Organ identity genes and pattern formation in flower development: Normal flower development

from Campbell, 6th edition

A set of homeotic genes, in different combinations, yield the different floral organs.

A CB E

Figure 21.20b Organ identity genes and pattern formation in flower development: In situ hybridization

from Campbell, 6th edition

The evolutionary determination of sepal and petal.

A CB2

B1

B3

Topics in Development

4. Homeotic genes a. the determination of appendage identity on fruitfly segmentsb. the evolution of form in segmented animals

4. Morphogenesis in Plants5. Organ identity genes in flower development