Gastrulation

Question 1

What are the characteristics of a common vertebrate body plan?

Answer 1

notochord
hollow dorsal neural tube with distinct brain vesicles
somites (extend to the tail)
pharyngeal arches
similar expression pattern of developmental genes

Question 2

What is derived from ectoderm?

Answer 2

epidermis
CNS (also partially PNS)
sensory organs
melanocytes

Question 3

What is derived from mesoderm?

Answer 3

muscles
bones
kidneys
gonads
adrenal glands
heart
blood

Question 4

What is derived from endoderm?

Answer 4

digestive tract
liver
pancreas
pharynx
thymus
thyroid gland

Question 5

Gastrulation morphogenetic movements are evolutionary conserved. What is emboly?

Answer 5

meso- and endodermal cells become internalized

Question 6

Gastrulation morphogenetic movements are evolutionary conserved. What is epiboly?

Answer 6

germ layers are spread and thinned

Question 7

Gastrulation morphogenetic movements are evolutionary conserved. What is convergence?

Answer 7

germ layers are narrowed dorsoventrally

Question 8

Gastrulation morphogenetic movements are evolutionary conserved. What is extension?

Answer 8

germ layers are elongated along AP axis

Question 9

When does the gastrulation start in xenopus?

Answer 9

when cell in the region of the grey crescent move inward –> dorsal blastopore lip formation

Question 10

What happens after DBL formation in xenopus?

Answer 10

cells of the animal pole spread out
push surface cells toward and across the dorsal lip (epiboly)
cells move into the interior of the embryo
form endo- and mesoderm
archenteron cavity (future digestive tract) becomes bigger, blastocoel dissapears
blastopore lip forms a circle (cells moving to the interior all around; yolk plug visible in the middle)

Question 11

What is the equivalent of DBL in zebrafish?

Answer 11

shield around the yolk

Question 12

Which cells drive convergence and extension of the embryo?

Answer 12

mesenchymal

Question 13

What is the difference between radial and mediolateral intercalation?

Answer 13

radial: several LAYERS intercalate along the radius of the embryo –> form fewer layers, but greater area
mediolateral: several ROWS intercalate along the mediolateral axis –> form longer and narrower array

Question 14

What is the equivalent of DBL in mammals?

Answer 14

primitive streak
and
Hensen’s node at the anterior end

Question 15

What happens during gastrulation in chick embryos?

Answer 15

1. primary hypoblast cells delaminate individually (form island cells beneath the epiblast)
2. secondary hypoblast cells (derived from deep yolky cells at posterior margin) migrate beneath the epiblast
   - come Koller’s sickle
   - incorporate island cells and push them anteriorly
   - secondary hypoblast forms beneath the epiblast
   = 2-layered blastoderm with blastocoel between them
3. as hypoblast moves towards A pole, epiblast cells collect at the region anterior to Koller’s sickle -> thickening -> PRIMITIVE STREAK with Hensen’s node at the A end

Question 16

What controls cellular movements during gastrulation?

Answer 16

movements coordinated with cell fate specification
for gastrulation movements, position of distinct identities along the axes is required
–> created by Wnt PLANAR CELL POLARITY PATHWAY (PCP)

Question 17

Which signals specify the mesoderm and endoderm during gastrulation?

Answer 17

Nodal paracrine signaling:

- Nodal in the vegetal pole

Question 18

In xenopus: what is the role of Wnt signaling in the embryo?

Answer 18

Dorsal enrichment of Dsh and GBP, accumulation of B-catenin -> Siamois and Twin proteins -> transcription of organizer genes

Question 19

Wnt &
B-catenin;
Nodal &
TGF-B role?

Answer 19

DV patterning

mesoderm induction

Question 20

What is the difference between conditional (regulative) development and autonomous development?

Answer 20

Conditional: early gastrula - fate of the transplant depends on the location in the host embryo (EXCEPT: DBL)

Autonomous: late gastrula - the fate of the transplant is already determined and develops as in the donor embryo