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Mechanism Of Brain Development > John Mason > Flashcards

John Mason Flashcards

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1
Q

Name ways in which neural migration can be observed

A
  1. In c.elegans and zebra fish where embryo is transparent migrating can be visualised directly (e.g. using GFP to track formation of lateral line in zebrafish)
  2. Can also be studied using cultured cells or slices of tissue (for vertebrates): slices of brain placed in tissue culture with crystal dye to track migration
  3. Indirect methods: can be useful in tracking neural crest cell migration in chick-quail chimeras. Dye injected into neural tube, a piece of quail embryo grafted to chick embryo. Cells from quail embryo still follow its designated routes of migration. Another method birth-dating utilised the incorporation of BrdU
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2
Q

Name three major models of migration

A
  • scaffold-guided
  • chain migration
  • individual migration
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3
Q

Which brain structure adopts the radial migration mode? And what is meant by radial migration?

A

The migration of cells in the cerebral cortex

Mode of migration where cells migrate from the centre of a developing structure towards its outer edge

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4
Q

Which structure adopts the chain/collective migration mode?

A

Olfactory interneurons in the olfactory bulb

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5
Q

What is meant by rostral migratory stream? And state the sequence of migrating olfactory precursor cells.

A

The path followed by migrating olfactory precursors from their birth place, subventricular zone to the olfactory bulb

  1. Birth - subventricular zone
  2. Migrate towards the lateral ventricle
  3. Followed the rostral migratory stream
  4. Reach the olfactory bulb and differentiate into olfactory interneurons
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6
Q

Describe chain migration

A

Cells slide along each other to reach its destination

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7
Q

What is the term for individual cell migration? And describe this mode of mirgation

A

Somal translocation - independent of any contact with glial cells.

Cells have long process towards the plial surface. This process progressively shortens as the neurons migrate towards the surface.

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8
Q

name the four steps in which neurons migrate

A
  1. initiation
  2. attachment (guidance)
  3. locomotion (movement)
  4. termination
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9
Q

what are the names of the molecules responsible for the initiation of migration?

A

cadherins, N-CAMs and integrins

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10
Q

what initiates the migration of neural crest cells?

A

the dynamic changes in CAM expression

e.g. downregulation of cadherin 6 and N-cadherin

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11
Q

name two major mechanisms in which migrating cells are guided to their destination

A
  • chemotaxis (chemorepulsant and chemoattraction)

- guidance by glial scaffold

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12
Q

what is the outcome when Wnt signalling is mutated in the migration of QL and QR in c.elegans?

A

the two cells migrate randomly along the anterior and posterior axis

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13
Q

name the two genes that was mutated which encodes Wnt and Wnt receptor in c.elegans

A

egl-20 (Wnt protein) and lin-17 (encode frizzled, Wnt receptor)

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14
Q

what is the mechanism which causes neural crest cells to only migrate towards the anterior side of the somite?

A

neural crest cells express Eph receptors

posterior side of the somite express ephrin (chemorepulsion)

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15
Q

what type of receptor does Eph receptor falls under and what does it mediates?

A

receptor tyrosine kinases (RTKs) which mediates cell-cell interaction (often repulsive)

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16
Q

Eph and Ephrin which one is a ligand and which one is a receptor?

A

Eph: receptors
Ephrin: ligand

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17
Q

what type of ligands are ephrinA and ephrinB?

A

EphrinA: binds to membrane through GPI links
EphrinB: transmembrane protein

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18
Q

what is the name of the CAM that is important in glial-guided cell migration in the cerebellum and which cells express it?

A

astrotactin, a cell surface glycoprotein and it it express by the migrating neurons in the cortex and cerebellum

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19
Q

what is the name of the CAM that is abundantly express in the leading edge of migrating neurons in the cerebral cortex and what does it do?

A

N-cadherins, allows strong interaction/ close association between migrating cells and radial glial cells

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20
Q

what process involving CAM id occurring at the end of a migrating cells in the cerebral cortex?

A

active process of removing N-cadherin from cell surface -> weaken interaction allows the tail of migrating neurons to dissociate from glial cell

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21
Q

describe the morphology of a migrating neuron

A
  • long, leading process extend towards direction of migration
  • centrosome position ahead of nucleus in direction of migration
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22
Q

describe the process of the changes in cell shape during migration

A
  1. leading process extends in direction of migration
  2. centrosome moves into the leading process, it contracts
  3. NUCLEUS move towards centrosome (nucleokinesis), remainder of cell body moves forward at the same time. The nucleus is attach to microtubule originating from the centrosome
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23
Q

the shape changes in cell during migration is mediated by …

which mechanism helps cells to propel forward?

A

cytoskeleton

actin-myosin contraction

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24
Q

which molecules regulate the stability of microtubules?

A

microtubule-binding proteins

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25
Q

what is the name of the disorder resulting from non-functioning cell migration and what is the characteristic of this disorder?

A

lissencephaly

  • smooth brain, lack of folding, sulci and gyri
  • epilepsy, mental retardation, motor impairment and lack of developmental progress
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26
Q

name the genes found to be defective in lissencephaly patients and what is this gene responsible for?

A

LIS1 - microtubule binding protein, complexes with dynein (microtubule motor), found at centrosome of migrating neurons. Coordinating movement of cytoskeleton which allows migration

Doublecortex (DCX): microtubule binding protein, promotes microtubule binding/stability

TUBA1A and TUBB2B: encode alpha and beta tubulin

27
Q

what is the name of the stop signal associated with the termination of migration and what does it encode? and where is it expressed?

A

reelin

Reeler encodes large extracellular glycoprotein named Reelin

expressed at high levels by Cajal-Retzius (CR) cells in cortex and GRANULE CELLS in EGL of cerebellum

28
Q

what is the outcome of reelin mutation in the cerebellum?

A

uncoordinated migration of purkinje and granule cells

cortical layers do not form normally

29
Q

what is EGL in cerebellum

A

external granule layer

30
Q

where does the GABAergic and excitatory neurons born in the areas of the telencephalon and what mechanism of migration do both neurons possessed?

A

GABAergic: born in the ventral telencephalon (medial ganglionic eminence). tangential migration

Excitatory neurons: ventricular zone. Radial migration

31
Q

how do axons find their way in terms of the steps and cues?

A
  • pathways consist of series of small steps

- guided by specific cues during each step

32
Q

what type of cells act as intermediate target for the migrating Ti1 pioneer neurones?

A

guide post cells

33
Q

what do pioneers axon do?

A

laid out the path for other axons to follow. these other axons are referred to as followers

34
Q

where are the environmental cues present that guides axon during migration?

A

surface of other cells or ECM

35
Q

what is selective fasciculation?

A

process in which growth cones distinguish among and extend along specific axonal surfaces

36
Q

name a form of contact guidance

A

fasciculation

37
Q

what is the evidence supporting the labelled pathway hypothesis?

A

axons expressing the same molecule would fasciculate with each other

38
Q

name CAMs involved in selective fasciculation

A

Fascicilin (Fas), Neuroglian (L1), NCAM and cadherin

39
Q

how to axons defasciculate?

A

interaction by beaten path protein which disrupt fascicilin homophilic interaction

40
Q

what is commissural axons? where is its cell body located?

A

axons that are important in coordinating movements between two sides of the body because they cross from one side of the body to the other

dorsal part of the neural tube

41
Q

which part of the SC expresses netrin? which process does this secreted molecule is involved in?

A

netrin is express in the floor plate (ventral midline) of SC

it is a molecule involved in guiding commsirual axons (chemoattractant)

42
Q

what are the two netrin receptors in c.elegans that are responsible for the attractive and repellent activity?

what are the homologues for mammals for the attractive cue receptors?

A

attractive: UNC40
repellent: UNC5

mammals: DCC and Neogenin

43
Q

during commissural axon projection, what was observed when it reaches the highest conc. of netrin?

A

they do to stop at the FP this means that axon can change responsiveness to cues

44
Q

fill in the blanks:

(receptor - ligand)
Eph - (1)
(2) - slits
(3) - netrins
plexins/neuropilins - (4)
A
  1. Ephrin
  2. ROBO
  3. UNC40/DCC (in mammals)
  4. semaphoring
45
Q

what kind of labelled could be used to track axon pathways?

labelling from cell body to growth cone is referred to as what type of labelling and vice versa?

A

fluorescent carbocyanine dyes e.g. Dil (crystal dye)

lipophilic dyes which diffuses throughout the lipid layer

cell body -> growth cone: anterograde labelling

growth cone -> cell body
retrograde labelling

46
Q

what is an open book culture?

A

neural tube being cut on the dorsal part to ‘open up’ the structure -> creates a flat culture

47
Q

what happened to the commissural axons when an ectopic FP was placed after the axons have crossed the previous FP?

A

commissural axons are no longer attracted to the FP and do not respond to netrin

48
Q

describe the observation in commissural axons for these mutations:

slit
robo1
comm

A

slit: attracted to the midline
robo1: cross the midline more than once (going round about)
comm: never cross the midline and did not form commissures

49
Q

what type of secreted protein is slit? where is it expressed?

A

slit is a repellent expressed at the midline glia. prevent inappropriate crossing of the midline

50
Q

if both netrin and slit is expressed by the midline glia then how can the commissural axons cross the midline the first time?

A

because commissural axons are only repelled by slit once the have crossed thus preventing recrossing

the determinant is which receptor is active in the growth cone

51
Q

what are the receptors for slit expressed in the midline?

A

ROBO 1 2 3 this accounts for the not completely gone sensitivity because the mutant is for ROBO 1

52
Q

if robo is a receptor for slit then why does robo1 mutant still confer some repellent to the midline?

A

because there are three types of robo receptors 1,2,3 and therefore robo1 mutant only cause some loss to repellent activity

robo 1,2,3 mutant resembles slit

53
Q

which receptor plays a critical role in change of sensitivity?

A

comm receptors

54
Q

name three main genes involved in commissural axon guidance and how are they discovered?

A
  • slit
  • robo
  • comm

forward genetic screening

55
Q

when is comm protein expressed in commissural axons?

A

they are expressed before the commissural axons cross the midline

56
Q

how does the axon able to approach the midline which expresses slit (chemorepellent) and what changes after the axon has crossed the midline?

A

by expression of COMM. comm protein prevents robo to reach growth cone. this results in axons being insensitive to slit and therefore able to approach the midline

after crossing the midline -> down regulation of comm

57
Q

what happens to commissural axon after crossing the midline and which signalling molecule is responsible for this activity?

A

commissural axons turns toward an anterior source of Wnt4

58
Q

what are the ways in which limited number of cues cannot navigate car number of axons?

A
  1. Cues act in combination (e.g. netrin and slit)
  2. same cue may act in multiple defects -> slit and robo
  3. influence of co factors in the interaction between some cues and their receptors -> e.g. HSPG (heparin sulphate proteoglycan). slits require HSPG to activate signalling.
59
Q

apart from the neural tube, what other cells does slit is involved in and what was observed in the phenotype?

A

retinal ganglion cell axons

mutant result in the axons being misnavigated but only for double slit mutant

60
Q

how does the growth cone able to have all these proteins while being far from the cell body?

A

local synthesis of the protein. shown by inhibitor of protein synthesis prevent axon navigation

61
Q

what was observed when the axon is cut separating the growth cone from the cell body in Xenopus retinotectal axons?

A

growth cone still able to respond and turn towards chemoattractant

62
Q

where does the cytoskeleton synthesised in projecting axon?

A

growth cone, experimental evidence shows the presence of cytoskeleton mRNA in growth cone

beta-actin mRNA showed to be transported to growth cone

63
Q

name three receptor-ligand pair that are involved in guidance of neural crest cells migration into somite

A

Eph - Ephrin
Slit - Robo
Neuropilin - Semaphorin

Mechanism Of Brain Development (2 decks)

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