BRAIN VS SPINAL CORD

Question 1

In the neural tube of the early embryo, different regions of the axis express different trasncription factors. Can you given an example?

Answer 1

Anteriorly - Otx2

Posteriorly Gbx2

Question 2

The nervous system becomes segmented into what regions?

Answer 2

Forebrain
Midbrain
Hindbrain
Spinal Cord

Question 3

Since the organiser self differentiated into three different tissue types: anterior endoderm and prechordal mesoderm and notochord. These involute and undergo convergent extension, elongating the neural tube above also. These three tissues are now different from one another and express different transcription factors to influence the neural plate above. How is anterior posterior identity affected?

Answer 3

The anterior endoderm and prechordal mesoderm express brain like transcription factors.
The notochord expresses spinal cord like transcription factors. This is one of the theories.

Question 4

What is the second theory in regards to regionalisation along the AP axis.

Answer 4

The activation transformation model.

Question 5

What is the activation transformation model?

Answer 5

Initially the entire neural plate is brain like under the influence of the anterior endoderm and prechordal mesoderm. Then, signals from the notochord cause cells at the posterior end of the nerual plate to proliferate and transform these cells from anterior identity to posterior identity ie turn on the transcription factors that dictate posterior identity.

Question 6

What signals are expressed anteriorly in the prechordal mesoderm and anterior endoderm to turn on brain like transcription factors?

Answer 6

Retinoic acid antagonists and Wnt antagonists and FGF antagonists are expressed anteriorly.

Question 7

What signals are expressed posteriorly in the notochord to turn on spinal cord like transcription factors.

Answer 7

Wnts and retinoic acid and FGFs are expressed posteriorly.

Question 8

The nervous system is very much segmented. How are these gradients of transcription factors transformed into distinct step like units?

Answer 8

There are two models:

1. Alan Turing reaction diffusion model
2. Lewis Wolpert French Flag model
   - cells respond to discrete threshold concentrations

Question 9

What does the gradient of retinoic acid along the AP axis induce?

Answer 9

Discrete expression of HOX gene transcription that then dictates segmental neuronal identities along said axis.

Question 10

Hox genes are highly conserved evolutionarily. What else has been shown?

Answer 10

Hox genes have been logged as the first evidence for homology between invertebrates and vertebrates.

Question 11

What is a HOX gene?

Answer 11

Homeobox DNA encodes DNA binding protein domain of 60 amino acids called the homeodomain.

Question 12

Interaction of the hindbrain cells and forebrain cells induces what?

Answer 12

At the boundary of these, the midbrain cells are induced.

Similarly, this progresses from the three primary brain vesicles to the five secondary vesicles and beyond.

Question 13

What are the three primary brain vesicles?

Answer 13

Forebrain (prosencephalon)
Midbrain (mesencephalon)
Hindbrain (rhombencephalon)

Question 14

What are the five secondary brain vesicles?

Answer 14

Telencephalon
Diencephalon
Mesencephalon
Metencephalon (afterbrain)
Myelencephalon (medullary brain)

Question 15

What does the telencephalon go on to form?

Answer 15

Cerebral Cortex
Basal Ganglia
Hippocampus
Olfactory Bulb

Question 16

What does the diencephalon go on to form?

Answer 16

Thalamus
Hypothalamus
Retina and Optic Nerves

Question 17

What does the mesencephalon go on to form?

Answer 17

Tectum

Fibre Tracts

Question 18

What does the metencephalon go on to form?

Answer 18

Pons

Cerebellum

Question 19

What does the myelencephalon go on to form?

Answer 19

Medulla