Lecture 6 (3a) Gastrulation Flashcards Preview

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Flashcards in Lecture 6 (3a) Gastrulation Deck (73):
1

Cleavage

rapid mitotic divisions
- in Drosophila, only nucleus
• After cleavage = blastula
- blastoderm in Drosophila

2

Gastrulation

transforming a hollow ball into a 3-layered structure
• INVAGINATION TO FORM LAYERS

3

Germ layer

main division into cell types

4

Evtoderm makes

skin and nervous system

5

Mesoderm and endoderm make

inner structures

6

Organogenesis

different tissues and organs from

7

Metamorphosis

larval stage to maturity

8

The life of a new frog begins with the

fusion of the genetic material of the sperm and egg
(fertilization)

9

After fertilization

female frog lays eggs

10

Animal cap
(brown part)

• ectoderm in blastula
• remove = form epidermis
= some intrinsic factors that specify genes
• take from different regions - they sort themselves, reconstruct themselves

11

The first process after fertilization

CLEAVAGE
eg 2-cell embryo to 8-cell embryo

12

Somite

lateral mesoderm to spinal cord forms muscles and vertebrae

13

Cleavage results in formation of the

blastula

14

The blastula is a

hollow ball

15

Cavity in the blastula is called a

blastocell

16

Gastrulation begins with the formation of a

slit in the future dorsal side of the embryo

17

After gastrulation

organs and tissues are formed
• eg neural groove (to become neural tube)

18

The cells that generate the 3 germ layers are

present in the late blastula

19

Mid-blastula transition

• shortly before gastrulation
• transcription is activated in the embryo

20

Both endoderm and ectoderm are specified by

maternal cell fate determinants
• animal half expresses maternal factor ENDODERMIN
+ zygotic factor FOX1E
• vegetal half expresses maternal factor VEGT
+zygotic factor NODAL (mesodermal induction)

21

Explants from animal cap form

ectodermal derivatives

22

Explants from vegetal cells form

endodermal derivatives

23

Explants from animal cap and vegetal cells form ectoderm and endoderm derivatives

AUTONOMOUSLY

24

Germ layer cells reconstruct their spatial relationship

after dissociation

25

In Xenopus, endoderm development is initiated by the maternal transcription factors

VegT and Veg1

26

VegT and Veg1 found in

endoderm

27

One maternal factor activates a cascade of

embryonic genes
VEGT ACTIVATES THE EXPRESSION OF MANY ZYGOTIC TRANSCRIPTION FACTORS

28

These transcription factors factors regulate each other and there expression is maintained by

Nodal

29

Nodal

• activated by VegT
• is a morphogen, especially in future dorsal and lower concentration to ventral

30

Nodal is a morphogen and accumulates in the

endoderm

31

Mesoderm

induced by Nodal and at same time told what type of mesoderm it is to form

32

Morphogen

proteins in concentration gradient
• cells respond to different concentrations
• instruct cells to adopt different cell fates at different concentrations

33

The nodal gradient determines

the type of mesoderm formed

34

Xnr is highest in

the dorsasl region

35

The various mesodermal fates are specified by

the Xnr gradient

36

Nodal is activated by

β-catenin + VegT + Vg1
--> gradient
--> different mesodermal cells
• organizer of dorsal structure
-- gradient ventral to dorsal

37

Additional factors required for mesdoerm induction:

VegT also activates the secreted factors activin and Derriere which in turn induce the formation of mesoderm by activating brachyury

38

Brachyury is expressed in

all mesodermal cells

39

In the late blastula, the cell fates of

the cell within the individual germ layers are determined
• additional signalling pathways such as Wnt and FGF are required for regional specification of the germ layers

40

Cells are made different

with different morphogens in different concnetration

41

Cell fates are determined in

the late blastula stage

42

The fate map varies in different vertebrae groups because

the cleavage pattern is different

43

Internalization of the endoderm and mesoderm occurs at

a dorsal area - the BLASTOPORE

44

Internalization is shown as a

slit (meso and endo)

45

Mesodermal and endodermal cells migrate towards the

animal pole

46

The ectoderm expands towards the

vegetal pole

47

Gastrulation varies in different groups but

the result is the same
• ectoderm
• mesoderm
• endoderm

48

Gastrulation in the human embryo

endoderm and mesoderm are internalized through the primitive groove

49

Epiblast

human embryo
• disc-like
• internalized at groove (meso and endo)

50

Formation of the germ layers in Drosophila melanogaster

• endoderm makes the midgut at poles
• the ectoderm forms the foregut and hindgut

51

In Drosophila the mesoderm is

ventral
• the endoderm is split into an anterior and posterior region

52

Germ cells are

NOT from germ layers
• germ cells are set aside before
(eg pole cells in Drosophila)

53

The mesoderm is

internalized

54

In vertebrates, the mesoderm forms

the muscles among others

55

At the same time as the mesoderm is internalized, the endoderm

invaginatese anteriorly and posteriorly

56

The endoderm forms the

midgut
(foregut and hindgut are formed by the ectoderm)

57

The midgut is subdivided into

4 chambers

58

The 3 germ layers give rise to

different organs and tissues
• the germ cells don't arise from the 3 germ layers

59

The notochord

induction of the nerve cord
• transient, forms mesoderm

60

Derivatives of the somites

• cartilage of vertebrae and ribs
• muscles of the rib cage, limbs, abdominla wall back, tongue
• tendons that connect the muscles to the bones
• dermis of the dorsal skin
• vascular cells of aorta and intervertebral blood vessels

61

Functions of the mesoderm

1. induces the mesodermal germ layer
2. induces the formation of several mesodermal organs (notochord, heart, blood vessels)
3. constructs the linings of 2 tubes within the vertebrate body - the digestive tube and the respiratory tube

62

The endoderm induces the formation of

several mesodermal organs
(notochord, heart, blood vessels)

Anterior endoderm BMP signalling
--> cardiogenic mesoder (heart)
&
--> hemangiogenic mesoderm (blood, blood vessels)

63

How is the gut endoderm regionally specified?

The areas of the digestive system are specified by regional transcription factors even before the endoderm forms a tube
• mesoderm instrutus the endoderm to different things
• boundaries in digestive system

64

BMP signalling

tells cells what to do

65

The stabilization of the boundaries results from

interactions with the mesoderm
• BMPs activate wnt signalling in intestine
• wnt inhibitors repress wnt signalling in stomach

66

Wnt

wingless in drosophila
• for boundaries
(engrailed for posterior border)

67

How are different areas initally specified in the endoderm?

• Shh gradient
• different Hox genes are expressed in response to different levels of Shh
• the mesoderm and endoderm "talk" back & forth
- induction both ways

68

Cleavage of the egg shell results in the formation of the

blastula

69

The cells that generate the 3 germ layers are present in the

late blastula

70

The 3 germ layers are separated during

gastrulation
• endoderm
• mesoderm
• ectoderm

71

The endoderm is specified by the maternal transcription factor

VegT

72

The endoderm induces the

mesoderm and some of its derivatives

73

The endoderm generates the

digestive and respirative tubes