Anterior and posterior regionalisation

Question 1

What is a cells competence

Answer 1

The past history of the cell

Question 2

Which part of the brain is formed first in development, what follows

Answer 2

Forebrain first, then mid and lastly hindbrain and spinal cord

Question 3

How does axial mesoderm move

Answer 3

Involutes and extends under the midline of the newly induced neuronal plate

Question 4

What would you find if you were to stop development at the point where axial mesoderm has just involuted below the midline of the neural tube - what molecular markers would there be

Answer 4

Expressing markers that are confined to the forebrain - when first induced - the neural plate is anterior in character

Question 5

How does the posterior nervous system develop from the initial axial mesoderm

Answer 5

The node changes causing the notochord formation which secretes signals that cause growth and posteriorization

Question 6

What is the activation - transformation model

Answer 6

Neural inducing molecules induce and maintain the anterior forebrain tissue. Initially come from early organiser cells but are then maintained by prechordal tissue once the organiser differentiates
Subsequently other signals then transform the tissue to a more posterior fate

Question 7

What are posteriorising signals antagonised by

Answer 7

Prechordal tissue

Question 8

Before gastrulation, what do cells in the organiser secrete

Answer 8

BMP/Wnt inhibitors - leads to the induction of neural tissue with an anterior character

Question 9

What do the cells of the organiser secrete after gastrulation

Answer 9

Only the cells that involuted first continue to produce BMP and Wnt inhibitors

Question 10

What three signals are posteriorising

Answer 10

Wnt,FGF and retinoic acid

Question 11

What gradient is found in the posteriorising signals

Answer 11

Highest concentrations are most posterior

Question 12

What does the neural plate differentiate into

Answer 12

Axial mesoderm - notochord and prechordal mesoderm

Question 13

What is being produced in the prechordal mesoderm

Answer 13

Wnt inhibitors and cerberus - very strong forebrain inducing activity

Question 14

What is anencephaly and how is it caused

Answer 14

occurs in humans where the forebrain is not maintained - due to the absence of transcription factors that maintain anterior character (Wnt inhibitors/cerberus)

Question 15

How are HOX genes activated

Answer 15

Threshold concentrations of posteriorising signals - those expressed in posterior regions only, are only responsive to high concentrations of signals
Those that are expressed along the whole body are sensitive to low concs of posteriorising signals

Question 16

How are HOX genes required in the formation of rhombomeres

Answer 16

In response to posteriorising signals - A HOX code is set up along the body axis, Differing concentrations/ different genes are required in the eventual establishment of hindbrain rhombomeres and the development of the cranial nerves