1

Lecture 6

Development of theDrosophila

Animal Development

2

Recipe for Animal Development

Differentiate: selectively activate gene expression

Make an egg

Cut it up

Move cell groups

Produce a three-layered embryos

3The reproductive system of the female Drosophila.

Accessory organs Wheresperm arestored.

(Wilt and Hake, Ch 3, 2004)

4

Oocyte materials:maternal components

The oocyte itself

The nurse cells

mRNA, proteins

mRNA, proteins, ribosomes and organelles

Follicle cells: somatic cells

5

Progressivedevelopment ofthe Drosophilaoocyte.

8-day journey (14 stages):Temperature-dependent

(Wilt and Hake, Ch 3, 2004)

6

Distribution and amount of yolk in eggs

Amount Distribution Occurs in Cleavage type

Isolecithal(sparse amount)

Mesolecithal(moderate amount)

Telolecithal(large amount)

Centrolecithal(large amount)

Even

Predominateson one side

Very dense,excludesCytoplasm toone side

Yolk in center

Many invertebratesmammals

Amphibia

Birds, reptiles, fish

Insect

Variable butcomplete

Radial

Incomplete,meroblastic

Surfacecleavage

(Wilt and Hake, Ch 2, 2004)

7

Egg development in Drosophila.

(Wolpert, Ch5, 2002)

8

The formation of nursecells, oocyte and ringcanals in Drosophilaoogenesis.CCytoplasmicytoplasmic bridgebridge

(Wilt and Hake, Ch 3, 2004)

9

The formation of nursecells, oocyte and ringcanals in Drosophilaoogenesis.

(Wilt and Hake, Ch 3, 2004)

10

The nurse cells

undergo duplications of chromosome

No cytokinesis

* Highly polyploid (256 x diploid)

* Large cells

11

The Drosophila egg chamber after yolk depositionhas started, stage 10A.

(Wilt and Hake, Ch 3, 2004)

12

Oogenesis in Drosophila

Meiosis

Genetic recombination

A stock piling of materials from theoutside

- nurse cells, fat body and follicle cells

A spatial ordering of these materials inthe oocyte

13

A developing Drosophila oocyte (right) isshown attached to its 15 nurse cells (left)and surrounded by a monlayer of 700follicle cells.

The oocyte and follicle layer are cooperating todefine the future dorso-ventral axis of the eggand embryo.

(Wolpert, Ch 5, 2002)

Gurken mRNA

14

Specificationof the antero-posterior anddorso-ventralaxes duringDrosophilaoogenesis.

Synthesized in the oocyte

Anterior end of the oocyte

Posterior end of the oocyte

(Wolpert, Ch 5, 2002)

15(Wolpert, Ch 5, 2002)

16

Fertilization in Drosophila

Sperm enters an opening in the chorioncalled the micropyle.

The egg is activated.

Meiosis is completed.

Syngamy takes places.

17

The first 8cyclestake placeevery 9min.

The nucleibegin tomigrate tothesuperficialcorticalcytoplasmic layer. Syncytial blastoderm

(Wilt and Hake, Ch 3, 2004)

18Cleavage and cellular blastoderm formation.

Pole cells: * the first true cells* form the primordial germ cells

The nuclei beginto migrate to thesuperficialcorticalcytoplasmic layer.

(Wilt and Hake, Ch 3, 2004)

19

Cellularization of thesyncytial blastoderm I.

(Wilt and Hake, Ch 3, 2004)

20

Cellularization of thesyncytial blastoderm II.

Cellular blastoderm

(Wilt and Hake, Ch 3, 2004)

21

Larva hatches and starts feeding

By middle of14

Extensive anteroposterior pattern and dorsoventralpattern are complete before morphogeneisis begins

Late in 14Morphogenesis begins

Early in 14Cell membranes form between cortical nuclei;Zygotic gene expression increases

9Pole cells bud off from the rest of the egg;A low level of zygotic gene expression occurs

7-10Nuclei migrate to the cortex

1-8Nuclear proliferation occurs very rapidly

CyclesActivity

Early development of Drosophilia

22

Cellular blastoderm

Syncytial blastodermAll nuclei are developmentally equivalent

Cellular fate has more or less restrictedalong particular pathway

23

ChimeraAn organ or tissue composed of cells fromtwo genetically distinct sources

An organism that consists of cells derivedfrom more than one individual (zygotelineages), usually of different genotype

More strict definition

24

Primary Chimaerasformed at a very early embryonic stage

Secondary Chimaeras

all tissues in the body are potentially chimeric

formed during later post-implantation or postnatalstages by tissue grafting or transplantation

only one or a few tissues might be chimeric

25

Mosaic

An organism that consists of cells of more than

one genotype

The genotypically different cells all derived from a

single zygote

More strict definition

26Transplantation analysis of pole cells and polar plasm.

(Wilt and Hake, Ch 3, 2004)

27

Cytoplasmic-nuclear interaction

Orthotopic transplantation

Heterotopic transplantation

28A fate map of Drosophila.

(Wilt and Hake, Ch 3, 2004)

29

Organization of the cellular blastoderm.

(Wilt and Hake, Ch 3, 2004)

30

Organization of the cellularblastoderm.

(Wilt and Hake, Ch 3, 2004)

31

Developmentally equivalent nucleigenerated during cleavage interactwith different cytoplasmic areas of theegg.

Losing totipotencyDetermination: process

32

Gastrulation inDrosophila I.

Ectoderm: blueMesoderm: redEndoderm: yellow

(Wilt and Hake, Ch 3, 2004)

33

Gastrulation inDrosophila I.

(Wilt and Hake, Ch 3, 2004)

34

The formation of neuroblasts.

Cell from the ventral surface move into the interior.The progenitor cell divides, giving rise to bothneuroblasts and glial cells (supporting cells of thenervous system).

(Wilt and Hake, Ch 3, 2004)

35

Invagination of epitelial cells

Germ band extension

Ingression of individual cells

Gastrulation in Drosophila

The entire suite of movements thatbegins when cells move interiorly andproduce the distinctive endoderm,mesoderm and ectoderm germ layers.

36

The registration ofembryonicparasegments withadult body segments.

(Wilt and Hake, Ch 3, 2004)

37

Imaginal discs in theDrosophila larva (a firstinstar larva).

(Wilt and Hake, Ch 3, 2004)

38A summary of the maternal effect genes determining pattern.(Wilt and Hake, Ch 3, 2004)

39

The suppression by nanos of posteriorhunchback.

The concentration of bicoid, hunchback and nanos mRNAat the time of fertilization.

(Wilt and Hake, Ch 3, 2004)

40

The suppression by nanos of posterior hunchback.After translation, high anteriorly for bicoid, high posteriorlyfor nanos.

(Wilt and Hake, Ch 3, 2004)

41

The suppression by nanos of posterior hunchback.At a later time in development, hunchback is very highanteriorly due to stimulation of the hunchback gene bybicoid, but Nanos continues to suppress hunchbacvkmRNA translation posteriorly.

(Wilt and Hake, Ch 3, 2004)

42

The pathway ofdorsoventralpattern.

(Wilt and Hake, Ch 3, 2004)

43

Interactions between the early oocytes andfollicle cells.

(Wilt and Hake, Ch 3, 2004)

44

Interactions betweenthe early oocytes andfollicle cells.

(Wilt and Hake, Ch 3, 2004)

45

Interactions between theearly oocytes and folliclecells.

(Wilt and Hake, Ch 3, 2004)

46

Epigenesis

The sequences of interactions betweentranscription factors and intercellularsignaling

NETWORKNot linear

47(Wolpert, Ch 5, 2002)

The relationshipbetweenparasegments andsegments in theearly embryo, lateembryo and adultfly.

48

Gap genes

Pair-rule genes (two-step process)

Segment polarity genes

Homeotic selector genes

Unstable TFs

unstable TFs

TFs and ligands/receptors

Specific identities

49

Gap genes

* Establishment of seven broad

* Set up conditions for regulating thepair-rule genes

By interacting with each other andproducts of the terminal axial system

Active in patterning the sevenrepeating stripes

50

Pair-rule genes* Lay down seven broad cellular stripes

around the circumference of theembryo

Segment polarity genes* Divide each of the broad stripes in

two, producing 14 narrower stripes,each with an identifiableanteroposterior polarity

51(Wilt and Hake, Ch 15, 2004)

The regulatorycascade forsegmentformation inDrosophila.

Gap genes1. interact with each

other and withproducts of theterminal (posteriorand anterior) axialsystems;

2. Set up conditionsfor regulating thepair-rule genes.

52(Wilt and Hake, Ch 15, 2004)

The expressiondomains of gapgenes.

Hb

Torso &torsolike

Tll

kr, kni, gt (posterior)

hkb, tll

gt (antierior)

53

Protein Genes whose expression is

Name Levels activated repressed

Bicoid High hb, gt

Hunchback high kr, gt, kni

intermediate kr

Low kr

Dorsal high in nucleus twist, snail dpp, zen

54(Wilt and Hake, Ch 15, 2004)

Regulation ofhunchbackby bicoid.

Bicoid

hunchback

55(Wilt and Hake, Ch 15, 2004)

The expression of pair-rule genes.

56(Wolpert, Ch 5, 2002)

The striped patterns of activity of pair-rule genes inthe Drosophila embryo just before cellularization.

57

15_14

(Wilt and Hake, Ch 15, 2004)

Early and late promoters of some eve stripes.

activate

repress

Later enhancer;Autoregulatory region

58(Wilt and Hake, Ch 15, 2004)

The structure of the regulatory module of evestripe 2.

Expression-inhibiting sites

Expression-activating sites

59(Wolpert, L. Ch 5, 2002)

The specification of the second even-skipped (eve)stripe by gap gene proteins.

60

15_17

(Wilt and Hake, Ch 15, 2004)

The expression domains of some segment polarity genes.

61(Wilt and Hake, Ch 15, 2004)

Interaction between wingless and engrailed.

62(Wilt and Hake, Ch 15, 2004)

An overview of the BX-C and ANT-C complexes.

63

•Positional identity of somites along the antero-posterior axis is specified by Hox gene expression

1. All homeobox genes encode TFs which contain a similar DNA-binding region

≒ 60 amino acids homeodomain helix-turn-helixDNA-binding motif 180 bp homeobox

2. Homeobox genes specifying positional identity alongthe antero-posterior axis originally identified in the fruit fly Drosophila

3. Homeotic transformation one structure replace another

4. Vertebrates - 4 separate clusters of Hox genes(Zebrafish has 6 clusters)

arisen by duplications of the genes within a cluster

64(Wilt and Hake, Ch 15, 2004)

The organization of the BX-C complex.

65(Wilt and Hake, Ch 15, 2004)

The organization of the ANT-C complex.

66(Wilt and Hake, Ch 15, 2004)

Posterior dominance of homeotic selector genes.