L10- Patterning the brain

Question 1

What is the forebrain?

Answer 1

Composed of the hypothalamus, cerebral hemispheres

Controls memory, sleep, perception

Question 2

What is the midbrain?

Answer 2

Composed of the tectum

Controls vision and movement

Question 3

What is the hindbrain?

Answer 3

Composed of the cerebellum, PONs, medulla oblongata

Controls movement, balance, autonomic functions (heart rate,breathing)

Question 4

What are the 3 primary brain vesicles?

Answer 4

○ Prosencephalon- forebrain
○ Mesencephalon- midbrain
○ Rhombencephalon- hindbrain

3-4 week embryo

Question 5

What are the 5 secondary brain vesicles?

Answer 5

○ Telencephalon- cerebrum
○ Diencephalon- hypothalamus
○ Mesencephalon- midbrain
○ Metencephalon- PONS, cerebellum
○ Myelencephalon- Medulla oblongata

Question 6

What are the two key signalling centres in the neural plate?

Answer 6

○ Anterior neural ridge- specieis telencephalon formation

○ Mid-brain hind-brain boundary (isthmus)- patterns boundary

Question 7

What are the 2 major steps in patterning?

Answer 7

1. Cell must be aware of its positions within a developing group- obtained by one or specific combination of signals
2. Interpretation of the positional address by the cell to manifest a certain cell type by expression of a particular set of genes

Question 8

What do morphogens do?

Answer 8

○ 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

Question 9

What are the signalling molecules patterning the anterior/posterior and dorsal/ventral axes?

Answer 9

○ Bmp (expressed everywhere)
○ Fgf
○ Wnt
○ Retinoic acid

Question 10

What is chordin?

Answer 10

A Bmp antagonist that is secreted by the organiser and promotes the formation of neural tissue (activation) - only anterior

Question 11

What do Wnts/Bmps do?

Answer 11

Wnts and Bmps allow posterior patterning of neural tube

There are inhibitors expressed anteriorly so their effects are only posterior

Question 12

What happens with different levels of Wnt?

Answer 12

+ Wnt= spinal cord
- Wnt= forebrain
medium Wnt= hindbrain and midbrain

Question 13

What do FGFs do?

Answer 13

They induce spinal cord from ventral ectoderm by forming neuroectoderm.
Bmps promote development into posterior neural tissue

Question 14

What does retinoic acid do?

Answer 14

Only required for posterior specification so not expressed more anteriorly (if expressed anteriorly then those structures are lost).

Question 15

How is the forebrain patterned?

Answer 15

Wnt inhibitors

Question 16

How do signalling molecules direct development of specific brain regions?

Answer 16

Regions are defined by domains of transcription factor expression in the neural plate

Question 17

What transcription factor is expressed anteriorly?

Answer 17

Otx2- midbrain

Six3, Irx- forebrain

Question 18

What transcription factor is expressed posteriorly?

Answer 18

Gbx2- hindbrain

Question 19

What is the isthmic organiser?

Answer 19

Forms at the boundary betwee midbrain and hindbrain and is needed to form the midbrain and crebellum
Boundary areas become secondary signalling centre

Question 20

What transcription factors in the isthmic organiser control patterning?

Answer 20

FGF8- midbrain and cerebellum

Wnt1- midbrain

Question 21

What controls the patterning of the forebrain?

Answer 21

Anterior neural ridge- signalling centre
Expresses Emx1 which allows telencephalon formation
Wnt antagonists (tlc) induce telencephalon

Question 22

What are rhombomeres?

Answer 22

Cell tight compartments that allow hindbrain segmentation
Neural precursors acquire there positional identities within rhombomeres
Defined by HOX genes

Question 23

How is the spinal cord organised?

Answer 23

The notorchord is an organiser of the ventral spinal cord and induces floor plate and motor neurons
Notorchord and floor plate secrete Shh