lecture 4

Question 1

A-P regions

Answer 1

anterior is brain and posterior is spinal cord

Question 2

what do ectoderm cells become?

Answer 2

SOX2 positive stem cells which inhibit BMP signalling or epidermal cells

Question 3

what do SOX2 stem cells become?

Answer 3

brain progenitor cells or spinal cord progenitor cells

Question 4

when the neural plate is induced

Answer 4

the cells are in the same plane and just beginning to change their relative position (inverlute)

Question 5

what happens after gastrulation?

Answer 5

some of ectoderm is induced to become neural plate and organiser cells undergo convergent extension and gastrulation and lying underneath neural plate

Question 6

organiser cells differences

Answer 6

not entirely uniform and have slightly different transcriptional factors
the cells closer to the endoderm and at the leading edge of the developing rod

Question 7

what organiser cells transcribe and secrete

Answer 7

all transcribe and secrete BMP antagonists but only a subset will also transcribe and secrete Wnt antagonists e.g. Dikkopf

Question 8

organiser cells that express Wnt antagonists

Answer 8

first cells to involute and will differentiate into prechordal mesoderm

Question 9

organiser cells that do not express Dkk

Answer 9

these will differentiate into notochord

Question 10

how the embryo is exposed to Wnt signalling

Answer 10

exposed with a gradient of Wnt signalling, posterior region is exposed to high levels of Wnt from posterior tissue during gastrulation and neurulation

Question 11

anterior portion with Wnt signalling

Answer 11

there is antagonists of Wnt signalling and have no Wnt signalling. for the brain, Wnt signalling has to be antagonised

Question 12

where is Wnt signalling secreted?

Answer 12

prechordal mesoderm

Question 13

how the sheet of neural tissue becomes regionalised

Answer 13

there is a signal of Wnt at one end and an antagonist of the signal at the other end

Question 14

evidence of Wnt signalling

Answer 14

there is discrete transcriptional signals using in-situ hybridisation for mRNA and immunohistochemistry for proteins

Question 15

where is SOX2?

Answer 15

in all neural plate/tube cells where Otx2 only in brain progenitors in the anterior region.

Question 16

evidence for pre-chordal mesoderm with organiser cells

Answer 16

• organiser cells from early gastrulation transplanted onto host embryo, there is a twined embryo because different cells will give prechordal and other will be norchrodal cells
• organiser cells from late gastrulation and transplant it, there is not a twined axis as the Wnt antagonists are lost

Question 17

pre-chordal mesoderm graft

Answer 17

graft into early gastrulate and the pre-chordal mesoderm and results in extra brain

Question 18

notachord transplant

Answer 18

will have posterior neural tissue induced with an extra spinal with Wnt signalling

Question 19

forebrain experiments

Answer 19

overexpression of Dkk as it is a Wnt antagonist
knock out of Dkk results in more Wnt signalling and no forebrain is developed

Question 20

Wnt signalling in mesoderm

Answer 20

there is graded signalling in mesoderm