Brain vs Spinal cord- Anterior vs Posterior Flashcards
Where are transcription factors Gbx2 and Otx2 expressed?
The TF Gbx2 is expressed posteriorly
The TF Otx2 is expressed anteriorly.
Regionalization od neural tube
The regionalization of the neural tube into these distinct A-P domains occurs when it is a still a long tube - ie before the flexures form.
Model 1:
Organiser differentiates to 3 different cell types: anterior endoderm (AE), prechordal mesoderm (PM)which lie under one end of neural plate/tube and notochord (NC) which lies under other end.
AE/PM mesoderm induces?
Notochord induces?
Anterio endoderm/prechordal mesoderm induce ‘brain-like’ neural transcription factors; notochord induces ‘spinal cord-like’ neural TFs
Model 2:
‘Activation-transformation’ model
• Initially, entire neural plate is ‘brain-like’ under influence of AE/PM.
• Then, signals from the notochord cause cells at the back end of the neural plate to proliferate and ‘transform’ these cells from an anterior to a posterior identity – ie turn off TFs that dictate anterior identity and turn on TFs that dictate posterior identity.
What is expressed anteriorly and posteriorly?
Retinoic acid and Wnt antagonists are expressed anteriorly (eg in PM/AE) and turn on brain-like TFs
Wnts and RA are expressed posteriorly (eg in NC) and turn on spinal cord-like TFs
What is defined through expression of the Tfs Hox genes?
Different domains of hindbrain and spinal cord
Retinoic acid gradient induces
Different patterns of Hox transcription
Describe a loss of function (knockout) experiment to examine the importance of
Hoxa1 and Hoxb1 are normally expressed in rhombomere4 and 5 - and the abducens nerve forms in this region. If a mouse knockout is created that lacks Hoxa1n and Hoxb1 (a double knock-out), then the mouse develops without the abducens nerve.
What do different cominbinations of Hox genes give?
give different regions of the neural tube along the axis a distinct ‘identity’. All descendants of that region will then go on to know ‘who’ they are, and so what to become.
Expression of Hox genes along A-P axis
Hox genes show expression along the A-P axis of the embryo -predicting and prefiguring later defined body segments in fly.
The Hox genes are activated by particular threshold concentrations of the posteriorizing signals. Those genes expressed along the whole axis and into the hindbrain are sensitive to low concentrations of the posteriorizing signals; those expressed only in posterior regions are only responsive to high concentrations.
Homeobox DNA encodes
a DNA-binding protein domain of 60 amino acids called the homeodomain.
An interaction between hindbrain and forebrain cells
induces midbrain cells at the boundary between these.
Further events result in regionalization of forebrain into diencephalon and telencephalon.
State some of the cell movements that occur as neural plate forms and lengthens
Invagination, ingression, involution, epiboly
Intercalation
Convergent extension
