Patterning the vertebrate body plan

Question 1

What is the neural plate

Answer 1

Group of cells from which all neural tissue is derived from

Question 2

In drosophila, what is the role of Dpp and Sog

Answer 2

Dpp and Sog dictate the dorsal and ventral sides of the developing body plan - Sog binds to Dpp and prevents it from therefore binding to Dpp receptors
This in turn causes surrounding cells to acquire a neural identity - neural cells develop in regions where Dpp is inhibited

Question 3

What is the vertebrate homologue of Dpp

Answer 3

BMP4

Question 4

What is the vertebrate homologue of Sog

Answer 4

Chordin

Question 5

Where are BMPs found in vertabrates

Answer 5

On the ventral side - chordin dorsal

Question 6

What is the key difference between vertebrates and invertebrates developing neural tissue

Answer 6

In invertebrates - single neuroblasts are formed from the delamination of surface ectoderm - go on to form neurons in small clusters (ganglia)
In vertebrates - Sheets of cells on the dorsal side of the embryo are induced to a neural identity - formation of the neural plate - this then rolls up to form the neural tube (neurulation)

Question 7

What is the specialised type of mesoderm that forms in the Xenopus oocyte

Answer 7

Spemann’s organiser

Question 8

What transcription factors are produced by Spemann’s organiser

Answer 8

Goosecoid, Xnot and Xlim

Question 9

What BMP antagonists are produced as a result of the specialised transcription factors

Answer 9

Noggin, Chordin, Cb

Question 10

How do Noggin, Chordin and Cb interact with BMP

Answer 10

Bind with a higher affinity than BMP to its receptors blocking its action
Also bind to BMP itself causing a conformational change in the protein - no longer can bind to receptor

Question 11

Where is BMP action inhibited

Answer 11

Entirely inhibited in the dorsal region of the embryo

Question 12

What will the inhibited cells go on to produce

Answer 12

Neural plate - surrounded by ectoderm that wasn’t exposed to BMP antagonists and remain as surface ectoderm

Question 13

How do chicks and humans develop differently

Answer 13

Chick embryos are a flattened disc known as a blastodisc

Question 14

What is the name of the specialised region of cells that secretes BMP antagonists in the chick embryo

Answer 14

Henson’s Node

Question 15

Where does Henson’s node develop

Answer 15

At the anterior end of the primitive streak

Question 16

What did Spemann’s experiments on newts show

Answer 16

Grafted the organiser from one newt embryo and grafted it onto the ventral side of another newt embryo
This induced a second body axis and second nervous system derived from the host cells ectoderm
Indicates that signals from the grafted tissue were sufficient to induce the host tissue to acquire a neural fate
Also provided the first evidence that Spemann’s organiser will differentiate into axial mesoderm which gives rise to the notochord

Question 17

How were BMP antagonists discovered

Answer 17

Through interrogating mRNA in organiser cells and looking for a transcript that would mimic the organisers ability to induce a secondary neural plate

Question 18

What are three features of a neural inducer

Answer 18

1. Must be expressed in the organiser
2. Overexpression at an ectopic site will cause the generation of a second body axis
3. KO should prevent axis formation