Problem:

In the early mouse embryo, the immediate environment of the somite comprises multiple tissues secreting different signalling molecules that pattern the somite.

Required:

Question 1: Which of these neighbouring embryological structures secretes Sonic hedgehog (Shh)?

Question2: Outline the Shh signal transduction pathway.

Question3: Describe the experiments in mice that showed that Shh is essential for the activation of myf5transcription in the early somite.

Question 4: In a somite cell, how does the myf5 genomic locus integrate the cell signalling in its local environment to regulatetranscription?

Explain all the answers in detail.