Patterning of the telencephalon - PICS

Question 1

Where are most morphogens located in the developing brain?

Answer 1

Midline

Question 2

What morphogens are located in the anterial neural ridge?

Answer 2

Fgf8 & other Fgf families

Question 3

What morphogens are located in the cortical hem?

Answer 3

Wnts and BMPs

Question 4

What morphogens are located in the anti-hem?

Answer 4

FGF15 - used to antagonise the affects of other Fgf family members at the anterial neural ridge

Question 5

What does the ventral part of the diecephalon express?

Answer 5

Shh

Question 6

What are the markers for the cortical hem?

Answer 6

Lhx2, Emx1/2

Question 7

What are the markers for the dorsal pallium?

Answer 7

Ngn12, Pax6

Question 8

What are the markers for the ventral telencephalon?

Answer 8

Mash1, Dlx1/2, Gsh 1/2

Question 9

What is the pallium and what kind of neurons are produced here?

Answer 9

Dorsal part of the forebrain and it makes glutamatergic projection neurons

Question 10

What is the tissue that forms in the pallium?

Answer 10

Choroid plexus and choroid roof aka the choroid field that gives rise to cells that produce tissue fluid

Question 11

What is the subpallium?

Answer 11

It is the ventral part of the forebrain

Question 12

What structure is in the subpallium and is made here?

Answer 12

Ganglionic eminences - produce GABAergic interneurons

Question 13

What is the cortical hem and what does it do?

Answer 13

Organising centre that’s vital for patterning of the cortex

Question 14

What does the archicortex give rise to?

Answer 14

This gives rise to the hippocampus

Question 15

What does the neocortical domain give rise to?

Answer 15

Cortex

Question 16

What is the paleocortex give rise to?

Answer 16

Many structures within the limbic system e.g. hippocampus and cingulate gyrus

Question 17

What are the dorsal markers of the telencephalon?

Answer 17

Pax6, Tbr2, Ngn2, Emx1

Question 18

What are the ventral markers of the telencephalon?

Answer 18

Gsh2, Gsh1 and Mash1

Question 19

How is the cortex affected by double mutants of Emx2 and Pax6?

Answer 19

Dorsal part appears to be reduced/ gone

Question 20

What happens if you completely eliminate Emx2 but leave one copy of Pax6?

Answer 20

The brain looks weirder but you will still have the expression of the dorsal markers

Question 21

What happens if you remove Pax6 but leave one copy of Emx2?

Answer 21

Brain looks quite weird but you can still detect some dorsal markers

Question 22

What happens if both Emx2 and Pax6 are ablated from the brain? (4 marks)

Answer 22

No dorsal markers

This shows there is no dorsal plate (tissue) and any left over tissue could be ventral

However it may be positioned dorsally but because its ventral tissue the markers are ventral

Question 23

What do ventral (subpallial) markers do in Pax6 mutant embryos?

Answer 23

The markers expand dorsally

Question 24

What happens to the cortex in the absence of Pax6?

Answer 24

Ventral marker DLX moves up with the cortex.

No Pax6 expression means that Mash1 is no longer restricted to the ventral region

Question 25

What does the roof plate (uppermost dorsal part in neural tube) do? (2 marks)

Answer 25

• It invaginates at the level of the forebrain, and produces separation of the 2 hemispheres
• As it does this it specifies the different structures i.e. cortical hem, hippocampus and choroid plexus

Question 26

What happens if the roof plate is removed?

Answer 26

Reduced expression of Lhx2 in forebrain

Smaller hemisphere

Question 27

What do the effects of removing the roof plate show us?

Answer 27

That something is needed in the roof plate to stimulate the expression of Lhx2

Question 28

What specific morphogen is expressed in the roof plate?

Answer 28

BMPs - these promote expression of Lhx2

Question 29

How experimentally can you prove that BMPs are needed for Lhx2 expression and what does this show?

Answer 29

So - put beads containing BMP4 into forebrain explant
It was found that if you put the beads in it or around it there is no Lhx2 expression
Whereas if you put it at the border of empty cell, there is slightly higher Lhx2 expression
Shows the occurrence of regulation

Question 30

What is the importance of Lhx2 expression?

Answer 30

With no Lhx2 expression found there’s a loss of cortical progenitors and neurons. Choroid plexus thickens and stretches up and round more of the cortex

Question 31

What happens to the choroid plexus in the absence of Lhx2 expression?

Answer 31

Choroid plexus becomes more medial, marker Ttr is absent

Question 32

What happens to the cortical hem in the absence Lhx2?

Answer 32

Wnt2b is not expressed and the structure becomes more medial

Question 33

What happens to the telencephalon in the absence of Lhx2?

Answer 33

Foxg1 is not expressed and the structure condenses