Dorsoventral Patterning of the CNS Flashcards
what is the purpose of neuralation
transforms mediolateral into dorsoventral polarity
what does the dorsal SC contain
interneurons
what does the ventral SC contain
motor neurons and interneurons
where do afferent fibres project
towards the CNS (contain pseudounipolar neurons)
where do efferent fibres project
motor axons
what does a gain of function experiment show
sufficiency
what does a loss of function experiment show
requirement
what does the floorplate and notochord secrete
Shh (sonic hedgehog) which patterns the ventral SC
what does Shh loss of function cause
malformed head
affects limbs
what is HB9
antibody against genetic markers of motor neurons
Shh gain of function experiment (ex vivo)
piece of lateral neural plate
interneuron region
1nm Shh - motor neurons
10nm Shh - floorplate
dose dependent induction of ventral neural progenitors
French Flag model requirements
specifies multiple cell fates (>2)
acts over distance (multiple cells)
acts directly on receiving cells
receptors in the Shh signalling pathway
PTC - multimembrane transmembrane that sits on primary cilia in absence of Shh
SMO - GPCR
GLIr
TF repressor
inhibits gene expression
SMO move to cilia via exocytosis
PTC moves intracellular
GLIa
TF activator
GLI activity gradient
less Shh - GLI3R
more Shh - GLI2A
GLI1A
Class I & Class II homeodomain transcription factors
Dbx2 - Class I - TF in dorsal spinal cord - low Shh
Nkx6.1 - Class II - TF in ventral spinal cord - high Shh
sharp boundaries, no overlap
what does Shh activate and repress
Shh represses Class I TF Pax6 expressed in absence of Shh
Shh activates Class II TFs Nkx2.2
Gain of function chick in vivo electroporation
B-actin enhancer - GFP (transcribes and expressed)
inject DNA via needle
DNA (-) ectopic (+)
cheap and easy
mutual repression of Class I and Class II TFs
Class I Pax6 expressed dorsally downregulates Nkx2.2 (expressed ventrally)
Nkx2.2 does not downregulate Nkx6.1
pax6 represses Nkx2.2, nkx2.2 represses pax6
class I and class II sharpened by mutual expression
role of orthogonal gradient
pattern the neural tube in a quasi-cartesian coordinate system
morphogens: Shh and Wnt
ventral midbrain (tegmentum) patterning
in concentric arcs which express transcription factors (FOX2A,PHOX2A,GATA2, Hx)
what does Shh duplication in the MB cause
duplication of arcs
what do Shh mutants cause
holoprosencephaly
HPE
FB disorder
