Neuronal migration 1,2,3 16.11 Flashcards
Wher are the vast majority of neurons born?
Ventricular zone
What are the main migratory routes in the developing brain for different neurons?
(2 marks)
- Projection neurons: generated in ventricular zone migrate radially up
- Interneurons: generated in ventral part of brain in ganglionic emminences - move tangentially up to cortex
What kind of migration is present in the cerebellum and pons?
In both cerebelleum AND pons: transgential mirgation
Cerebellum only: radial migration
Where are cajal restzius cells produced?
(2 marks)
In cortical hem, antihem, and anterior neural ridge, migrate transgentially over brain surface and cover completely
How does the pre-plate lead to the formation of cajal retzius cells in the marginal zone?
(3 marks)
- @ v early stages of development have pre-plate on top of ventricular zone
- Pre-plate has future subplate neurons and cajal retzius cells
- 1st neurons that migrate split up into cajal retzius cells in marginal zone and sub-plate neurons at the bottom
What are meninges?
Membranes that protect the brain
Outline the migration of cajal retzius cells.
(4 marks)
- Move on surface of brain where meninges located
- Meninges provide physical substrate and CXC42/ CXCR4 signalling - restricts movement of CR cells to most superficial part of marginal zone
- Eph/ ephrin - mediated contact repulsion mediates homogenous distribution over the brain
- Due to ^^ don’t get areas with high cell count or completely devoid of cells
How does migration happen in cortical interneurons?
(4 marks)
- Attractants in cortex
- Repellents in striatum form of Sema 3A/3F
- Migrate through leading, sense environment and look for cues
- Centrosome and nucleus move in an established branch
Pic: orange - area of high concentration of attractants, so branch nearest to it move towards it and other one is retracted. Have movement of interneuron to where centrosome and nucleus move into established branch
How do projection neurons migrate?
- Radially
What experimental methods can be carried out to view the migration of projection neurons?
(6 marks)
- In utero: use electroporation
- Apply electrical currents to palsmid DNA
- Progenitors will take up plasmid and express what’s in it and neurons will take it up
- Gets diluted as no more plasmid because given to neurons
- Can put on specific promoter
- After few days can see migration of plasmid
- Band at E18 is missing, then know something gone wrong
What is the first type of neuron generated in the deep layers?
Projection neurons
By the time the first deep layer neurons are generated, what is the cortex looking like?
(2 marks)
NO CORTEX
- Cortical wall very thin
What is somal translocation?
(2 marks)
- When cells go through multipolar pahse and because cortex thin, leading process contacts marginal zone
- Once contacted, stabilise there - cell will put itself up, moving nucleus up
How does glial giuded translocation occur?
(3 mark)
- Use process from RG cells as they act as a scaffold
- Attatch to process and migrate along process until close enough to marginal zone
- Leading process can stabilise itself and established itself quiety
What do neurons use as a basis for glia guided locomotion?
Radial glial processes as a scaffold to move up
What are the phases of the locomoting stage?
(3 marks)
- Swelling formed, in leading process of ahead nucleus and centrosome moves into swelling
- Nucleus the follows and moves into swelling
- Leading process extends further forming new swelling
- Repeat
What are the molecular pathways involved in the phases of locomoting stage?
What do adhesions do?
(2 marks)
- Cadherins mediate attatchment between neuronal processes and RG fibres
- Cadherins i.e. CDH2, CDH4 - cooperate to regulate migration in mouse brain by protein tyrosine phosphotase 1B.
What can be seen in a dominant negative mutant of CDH?
(3 marks)
- Neurons stuck in the intermediate zone and intefere with normal CDH function
- multipolar neurons aren’t stuck as their neurons formed a leading process that’s properly oreintated to the CP, but nuclei remain in IZ
- Neurons have ‘wavey’ processes and much less associated with RG processes
What group of GTPaeses regulate cadherin levels at the surface of migrating neurons?
RabGTPases
What is the role of Rab5 within the cell?
Controls endoyctosis of CDH
What is the role of Rab11?
Necessary for recycling endocytosed CDH back to the membrane
What can be seen in the dominant negative mutant Rab5?
- Neurons fail to migrate to cortical plate and show excess of N-CDH2 on surface
What can be seen in dominant negative mutant of Rab11?
- Migration defects - surface levels of N-cadherin 2 are lower, as NCDH2 stays inside the cell - isn’t recycled back to membrane
What two molecules accumulate inthe leading process of normally migrating neurons?
Actin and Moesin lycin kinase (MLK)
What is moesin lycine kinase used for?
Acto-myosin activity which is also in the leading process
What does blocking actomyosin activity do?
Stops nuclear movement
What is a kimograph?
Generated by taking images of migrating neurons at specific intervals and the images are compressed after
What does the drug blebbistatin do?
(3 marks)
- Myosin II inhibitor
- Inhibits somal movement
- Stops movement of nucleus, but centrosome still able to move into swelling.
What is nucleokinesis?
Saltatory forward movement of nucleus
How does Lis1 RNAi and Dynein HC RNAi interfere with nucleokinesis?
- Lis1 RNAi - completely blocks movement of nucleus and centrosome
- Dynein HC RNAi - blocks movement of nucleus only
What components form a complex with Dynein?
Lis1, Nde1, Ndel1
What are some of the effects seen in:
Lis 1 -/+
Lis 1 -/-
Lis 1 -/+: Cortex basiclly normal - see migration defects in hippocampus with splitting of hippocampopyrimidal cell layer
Lis1 -/-: Disappearance of hippocampus and very small cortex with lamination and fate specific defects
What are some of the effects seen in:
Ndel 1 -/+
Ndel 1 -/-
- Ndel 1 -/+: pretty much normal
- Ndel1 -/-: disorganisation of pyrimidal layer in hippocampus. In cortex, disorganisation of layers due to migration defects
Cytoskeleton and nucleus coupling:
- don’t know how to put this in a question so here is the info -
- For coupling, Lis1, dynein and DCX are essential
- Mutation in DCX causes neuronal migration defect - over exress migration rates
- Proteins cannot connect dynein and Lis 1 to nuclear membrane
- ^ proteins are Syne 1/2, SUN 1/2 - mutations in these leads to migration defects in which nuclearkinesis is impaired
What is the correct order of the different zones in the developing brain?
(5 marks)
Ascending order:
- Marginal zone: low cellular density, cajal RC
- Cortical Plate: projection neurons accumulate and formation of layers
- Intermediate zone: neurons cross here, less dense in cell bodies, more dense in neuropril e.g. projections
- Subventricular zone: neurons generated
- Ventricular zone: neurons generated, right on ventral surface
Where does multipolar migration and MP-BP transition happen?
Intermediate zone
What specific axons does the intermediate zone receive during multipolar migration?
Thalamocortical azons arriving to the cortex
Why is a multipolar morphology needed for migration?
(4 marks)
- Cortical neurons expand axons at same time they migrate
- Neurons that want to move to cortical plate have to traverse area full of horizontal axons
- Need multipolar morphology to navigate over area
- In process of becomign neurons, they extend and retract processes until one of them gets specialised
What are the molecular pathways involved in MP-BP transition?
(5 marks)
What is the mutant phenotype for protein Filamin A?
Actin binding protein, mutations will impair migration in multipolar phase
What is the phenotype for a mutation in Lis 1?
(3 marks)
- Loss of function either from mutation or RNA interference (RNAi)
- Arrest neurons in MP phase
- Neurons not able to transition to become bipolar
What is the phenotype for a mutation in DCX?
- Genes mutated in another form of lisocephalin - intefere with function of cells
- Can’t transition from MP to BP and can’t move up
- Too much DCX causes excesss of bipolar cells in areas it shouldn’t be
What are cyclin dependent kinases?
Proteins important in regulating cell cycle
What is cdk5 used for?
Necessary for neuronal polarization, correct lamination and migration
NOT INVOLVED IN REGULATING CELL CYCLE
What can be observed in a Cdk5 KO?
(6 marks)
- Cells don’t move up
- From E14.5-P3 - not one form of migration
- Neurons stuck in multipolar phase - specific impairment in MP to BP transition w/in SVZ-IZ in cell autonomous manner
- No layer 1 and white matter
- Later born neurons for layers II & V located under subplate in mutant cortex
- Neurons normally in upper layers now found in deep layers
What happens in both p35 and p39 KO?
- If just one, can recognise marginal zone at the top
- If both get same effect as seen for Cdk5
What proteins are phoshporylated by Cdk5 and what process are they involved in?
(2 marks)
Filamina and Dcx
Migration
What is a periventricular nodule heteropia?
(3 marks)
- Clinical defect caused by mutations in Filamin A or ARFGEF2
- neurons fail to locate to ventricular zone and form nodules close to ventricle
- Symptoms: seizures, dyslexia, movement problems
What is subcortical band heterotopia?
(4 marks)
- Double cortex syndrome - caused by mutations in DCX (x-linked, SBH in heterozygous females)
- Band of neurons located below what would be cortex
- Neurons leave VZ but fail to enter CP
- Symtpom: epilepsy
