Ventralization of the neural tube Flashcards
What is happening to the notochord at the same time that the neural plate/neural tube is forming
Notochord comes to lie at the ventral side at the midline of the neural tube
What does an ectopic notochord give rise to
Different signalling creates a secondary floor plate/ secondary set of motor neurons
What is the secreted factor from notochord/ floorplate in drosophila
Hedgehog - sonic hedgehog in vertebrates
Where is Shh found in the neural tube
Acts as a morphogen - high concentration at the ventral side of the tube - diffuses to dorsal side at low concentrations
What does Shh cause in progenitor cells
Causes them to produce transcription factors which confer ventral neural tube identities, progenitors will ultimately give rise to to cells that differentiate into ventral neurons
How do morphogen gradients used to establish progenitor domains
Made up of proliferating bands of cells - established through opposing morphogen gradients - Over time these differentiate and move laterally to form the defined neurons of the spinal cord, they then send out axons
What is the Hh signalling pathway
Ptc is a membrane receptor that, when not bound by Hh is inhibiting the action of another membrane bound protein, Smo
When inhibited Smo can’t act on Gli2/3 which in the absence of Hh are in their repressor form so enter the nucleus and prevent gene activation
Where is Shh expressed in vertabrates
Along the whole A-P axis and is always ventral
How does Shh signalling intersect with the HOX code
Intersects with the HOX code that gives A-P segmentation
This means that motor neurons develop at the ventral region of the spinal cord
What neurons develop ventrally in the hindbrain
A small cluster of serotonergic neurons
What neurons develop ventrally in the midbrain
Dopaminergic neurons of the substantia nigra form
How does Shh signalling cause differing neuron development
Differing concentration gradient of Shh
