Neuronal Migration

Question 1

Percentage of cortical neruons

Answer 1

70-80% Pyramidal projection neurons

20-30% Interneruons

Question 2

The diversity of cortical
GABAergic interneurons
is defined by which
properties:

Answer 2

• neurochemical content
• axonal morphology
• electrophysiology
• subcellular targeting
• Connectivity

Question 3

How many interneruons subtypes have been disocvered in CA1 area

Answer 3

21 - GABAergic to inhibit pyramidal neruons

Question 4

How many subtypes did RNAseq disocver in 2016 in mouse visual cortex

Answer 4

761 GABA cells 23 subtypes

Question 5

How many subtypes did RNAseq disocver in 2018 in mouse visual cortex

Answer 5

10,534 GABA cells
61 transcriptomic subtypes identified in the mouse visual cortex

Question 6

What the 5 main interneruons subclasses

Answer 6

1.Somatostatin
2.Paravbulin
3.Lamp5
4.Sncg -synuclein gamma
5.VIP

Question 7

Wnhat did they do in 2020 to discover 28 met-types of interneurons

Answer 7

multi-omic approach MET
in mouse visual cortex

Question 8

MET meaning?

Answer 8

met= Morphology, electrophysiology, transcriptomics

Question 9

How many subtypes do each subclasses have?

Answer 9

1.Somatostatin - 13
2.Paravbulin - 5
3.Lamp5 -2
4.Sncg -3
5.VIP - 5

Question 10

Which subclass is main interneuron?

Answer 10

Parvalbumin

Question 11

Nkx2.1 marker of..

Answer 11

Nkx2.1- marker for interneurons especially coming from MGE

Question 12

What is the dorsal (top) section of coronal section called?

Answer 12

Pallium

Question 13

What is the ventral (bottom) section of coronal section called?

Answer 13

Subpallium

Question 14

Where do cortical projection interneruons arise from

Answer 14

cortical precursors

Question 15

Where do cortical interneruons arise from?

Answer 15

Subcortical basal forbrain regions (MGE) and migrate into cortex during development

Question 16

How did they track MGE-derived interneruons to cortex

Answer 16

GFP lablled all over brain

Then transplant GFP cells into MGE of WT.

You see them migrate from MGE to cortex within 4 days

Question 17

Where do LGE cells migrate and who did the study

Answer 17

Wichterle et al 2001

neocortex and olfactory bulb

Question 18

2 Caveats of in utero transpaltation of GFP cells

Answer 18

1.Contamination
Transplantation experiments are subject to contamination from migrating cells.

2.Cross migration
MGe transplants include cells migrating through the MGE from other regions

Question 19

Instead of using in utero transplantation- what method did Kessaris create

Answer 19

Genetic approach - Cre-Lox genetic fate-mapping

transgenic mice and permantly labelling certain cells with GFP

Question 20

Why was NKX2.1 marker chosen for Cre fate mapping (Kessaris et al)

Answer 20

Originates in MGE and labels

Question 21

How did kessaris observe the migration- 2 technqiues

Answer 21

mRNA in situ hybridisation

Immunohistochemistry- GFP

Question 22

How did they fate map the interneruons arising from the LGE

Answer 22

Caveat: there was no marker that labelled especially the lateral ganglionic eminence using this approach. To improve this, they created a mouse that expresses venus, and subtracted (last image) subtractive approach to image the lateral ganglionic eminence

Question 23

Which subcortical regiosn does not produce interneruons for neocortex

Answer 23

Septum

Question 24

Which marker identified dorsal MGE cells

Answer 24

NKx6.2
SST+
CR+

Question 25

Which marker identified MGE cells

Answer 25

NKv2.1 & Lhx6 Pvalb and SST

Question 26

Which marker for CGE cells

Answer 26

Dlx1-Venus NKx2.1 VIP, RLN+SST, CR, NPY

Question 27

What has research not been able to do so far?

Answer 27

So far have not been able to genetically label these regions to determine whether they give rise to distinct interneuron subtypes.

Question 28

How have transcriptomics been used to explore subtypes of the subclasses futher?

Answer 28

--return to this part of lecture

Question 29

How has Kessaris explored subtypes futher

Answer 29

Comparative transcriptomic analysis of MGE- and CGE-derived cortical interneurons at different stages of development. The aim was to look for markers expressed in MGE and not CGE at e.g. at the embryonic stage and not the adult stage

Question 30

When did kessaris say diversity in interneruon subtypes arise

Answer 30

In the MGE before migration to cortex

Question 31

What is MTG8 (inclu other names)

Answer 31

MTG8 is a non-DNA-binding cofactor It is expressed in the MGE lineage Other names -Eto or RUNX1T1

Question 32

What does MTG8 interact with and what happens (Asgarian et al 2022)

Answer 32

MTG8 interacts with the pan-MGE transcription factor LHX6 and together the two factors promote expression of critical cortical interneuron subtype identity genes

Question 33

What did (Asgarian et al 2022) suggest about Diversity of cortical interneruons

Answer 33

transcriptional co-factors and modifiers of generic lineage specification programs may hold the key to the emergence of cortical interneuron heterogeneity from the embryonic telencephalic germinal zones.

Question 34

Where is MTG8 vs MTG16 expressed

Answer 34

High levels of MTG8 (all over) MTG16 (only in MGE)

Question 35

Where is LHX6 expressed

Answer 35

master regulator of cortical interneuron fate - expressed in the SubVentricular zone in the mantle.

Question 36

Where is MTG8 expressed?

Answer 36

Expressed in the SVZ of the MGE of the telencephalon. Mtg8 also expressed in the cortical plate (precursor for the cerebral cortex) Conclusion mtg8 expressing int highly expressed around day 14.5 then downregulated.

Question 37

What happens when you KO MTG8

Answer 37

Mtg8 -/-: Normal migration of MGE interneurons into the cortex Reduced number of Sst interneuron subsets. More Pvalb interneruons created (evidence from MTG8 mutant transplant study)

Question 38

Role of MTG8?

Answer 38

Interneruons specification into SST+ BEFORE migration to cortex

Question 39

What is the MTG8 transplant study and what did it show?

Answer 39

Transplanted MGE cells from Mtg8-/- embryos: reduced numbers of SST interneurons They isolated dissociated MGE cells from the Mtg8 mutants. They also have a control which was MGE from a WT embryo Dissociated both and transplanted into newborn pups' cortex in different regions. Looked 40 days later Results: -The experimental transplanted MGE cells with the Mtg8 mutant showed the exact same phenotype as the previous experiment -Observed reduced number of somatostatin expressing interneurons. -Observed increased PV interneuron subtypes- so the hypothesis is that Mtg8 mutants cause less somatostatin cells specified but more but more PV cells are created. However, they tested this and it wasn’t because of Mtg8 but because of cell death that increased the number of PV interneurons by a small amount.

Question 40

What is th role of LHX6

Answer 40

Lhx6 is crucial for specification of MGE interneurons, crucial for Pvalb and SST interneurons specification.

Question 41

LHX6

Answer 41

Key DNA-binding MGE transcriptional regulator

Question 42

Redcution/deletion of either MTG8 or LHX6 causes?

Answer 42

Reduction/deletion of either one of these genes results in a similar phenotype, namely, reduction of Sst cell specification

Question 43

Do MTG8 and LHX6 work togther?

Answer 43

Share genes so when they are knwocked out 5 simlar genes also downregulate -Sst, NPY, Thbs1, Npy2r, Galnt6

Question 44

What is required for SST or NPY interneruons to be specified

Answer 44

Need expression of both LHX6 and MTG8 in the MGE to specify before migration

Question 45

Possible mechanism of action of MTG8 and LHX6

Answer 45

MTG8 may stabilise LHX6 onto target sites and attract other factors onto the complex