Patterning of the brain - organising centres - PICS Flashcards
What are the organising centres?
Anterior neural bridge, Zone limitans intrathalamica, Midbrain-Hindbrain boundary
What are organizers?
Group of cells that secrete morphogens
What are the axial mesoderm/ endoderm and what do they express?
Non-neuronal tissue but express Otx2, Wnt, Fgf and RA which induces the signalling of Gbx2
What does it mean that the TF Otx2, Wnt, Fgf and RA are at adjacent boundaries?
It means there will be cross-repression and at this point there will be expression of En
What happens posterior to cross repression boundary and what does this show?
Gbx2 will activate Fgf8 and repress Wnt1. This shows that Fgf8 is produced in the posterior part of the organiser and Wnt 1 is produced in the anterior part
What happens if Otx2 is expressed less than 50% and what does this cause?
So it cant be compensated with Otx2 so you get an extension of Gbx2 rostrally but the same signalling factors produced for Otx2 are there. This leads to a giant metencephalon
What does a reduction of Gbx2 cause?
Expansion of Otx2 caudally and no formation of the cerebellum but a BIG expansion of the midbrain
What does a transplantation of the midbrain-hindbrain boundary to the forebrain create?
An ectopic membrane
What does Wnt1 knockout in mice show?
No formation of the midbrain or cerebellum but the forebrain, diencephalon remain intact
How does the effect of Wnt1 knockout happen?
Is because the organiser sits between the zone of Otx2 and Gbx2 expression and above the floor plate that express Shh
What do the population of neurons receive on the Otx2 side?
Shh and Fgf8 influence and this forms the dopaminergic neurons of the substantia nigra
What do the population of neurons on the Gbx2 side receive?
2
Influence from Fgf8, Shh and Fgf4 which form serotonin from raphe nuclei.
Other population receives influence from BMPs and Fgf8 and form noradrenaline
What does the Zona limitus intrathalamica organise?
Thalamus and hypothalamus. Anterior to the ZLI hypothalamus forms and posterior to it thalamus forms
What is the wedge of tissue that separates the pre thalamus from the thalamus and how is it formed?
ZLI starts as wedge and its domain lacks expression of LFNG
As it starts to express LFNG, Shh expression starts to peak up to the ZLI, and the ZLI receives Wnt signalling on the other side
So get a wedge of tissue that separates the pre thalamus from the thalamus
What are the morphogen families that promote the formation of the ZLI wedge and where are they expressed?
Wnt and Shh are expressed in it
Fgf is expressed anterior to it