L10- Patterning the brain Flashcards
What is the forebrain?
Composed of the hypothalamus, cerebral hemispheres
Controls memory, sleep, perception
What is the midbrain?
Composed of the tectum
Controls vision and movement
What is the hindbrain?
Composed of the cerebellum, PONs, medulla oblongata
Controls movement, balance, autonomic functions (heart rate,breathing)
What are the 3 primary brain vesicles?
○ Prosencephalon- forebrain
○ Mesencephalon- midbrain
○ Rhombencephalon- hindbrain
3-4 week embryo
What are the 5 secondary brain vesicles?
○ Telencephalon- cerebrum ○ Diencephalon- hypothalamus ○ Mesencephalon- midbrain ○ Metencephalon- PONS, cerebellum ○ Myelencephalon- Medulla oblongata
What are the two key signalling centres in the neural plate?
○ Anterior neural ridge- specieis telencephalon formation
○ Mid-brain hind-brain boundary (isthmus)- patterns boundary
What are the 2 major steps in patterning?
- Cell must be aware of its positions within a developing group- obtained by one or specific combination of signals
- Interpretation of the positional address by the cell to manifest a certain cell type by expression of a particular set of genes
What do morphogens do?
○ Signalling molecules that act via a gradient
○ The response to morphogens is the expression of specific transcription factors in domains within epithelium
○ Expression of transcription factors influence cell fate/behaviour
What are the signalling molecules patterning the anterior/posterior and dorsal/ventral axes?
○ Bmp (expressed everywhere)
○ Fgf
○ Wnt
○ Retinoic acid
What is chordin?
A Bmp antagonist that is secreted by the organiser and promotes the formation of neural tissue (activation) - only anterior
What do Wnts/Bmps do?
Wnts and Bmps allow posterior patterning of neural tube
There are inhibitors expressed anteriorly so their effects are only posterior
What happens with different levels of Wnt?
+ Wnt= spinal cord
- Wnt= forebrain
medium Wnt= hindbrain and midbrain
What do FGFs do?
They induce spinal cord from ventral ectoderm by forming neuroectoderm.
Bmps promote development into posterior neural tissue
What does retinoic acid do?
Only required for posterior specification so not expressed more anteriorly (if expressed anteriorly then those structures are lost).
How is the forebrain patterned?
Wnt inhibitors
How do signalling molecules direct development of specific brain regions?
Regions are defined by domains of transcription factor expression in the neural plate
What transcription factor is expressed anteriorly?
Otx2- midbrain
Six3, Irx- forebrain
What transcription factor is expressed posteriorly?
Gbx2- hindbrain
What is the isthmic organiser?
Forms at the boundary betwee midbrain and hindbrain and is needed to form the midbrain and crebellum
Boundary areas become secondary signalling centre
What transcription factors in the isthmic organiser control patterning?
FGF8- midbrain and cerebellum
Wnt1- midbrain
What controls the patterning of the forebrain?
Anterior neural ridge- signalling centre
Expresses Emx1 which allows telencephalon formation
Wnt antagonists (tlc) induce telencephalon
What are rhombomeres?
Cell tight compartments that allow hindbrain segmentation
Neural precursors acquire there positional identities within rhombomeres
Defined by HOX genes
How is the spinal cord organised?
The notorchord is an organiser of the ventral spinal cord and induces floor plate and motor neurons
Notorchord and floor plate secrete Shh
