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Cell Bio & Developmental Genetics > Lecture 7 (3b) The Development of the Nervous System > Flashcards

Lecture 7 (3b) The Development of the Nervous System Flashcards

1
Q

Overview

A
  1. generation of neural stem cells in a single layer
  2. each stem cell produces a specific part of nerual tissue
    3.identify target cells and form synapses
    form networks
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2
Q

Neurogenesis can be subdivided into 4 processes

A
  1. generation of neural stem cells
  2. establishment of neural stem cell indentity
  3. differentiation of neural precursors
  4. establishment of neuronal networks
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3
Q

The regions that will give rise to the different parts of the embryo are

A

already determined at the blastoderm stage

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4
Q

The neural cells move into the

A

embryo

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5
Q

The ventral nerve cord is

A

simpler than the brain

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6
Q

The ectoderm forms

A

ventral stem cells and makes skin cells

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7
Q

In order to generate all the different cell types of the nervous system, cells go through different stages of development

A
  • competence
  • specification
  • determination
  • differentiation
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8
Q

Neural epithelium goes from a single layer

A

to the neural and skin cells

• have to make competent with specific signals (proneural genes in scattered clusters)

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9
Q

Competence =

A

proneural genes expressed in clusters

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10
Q

Competence

A

all the cells in the neuroectoderm can also become neural cells if they are exposed to the appropriate combination of signals

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11
Q

The appropriate signals that lets the cells in neuroectoderm become neural cells

A

proneural genes

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12
Q

Proneural gens are required for

A

neural stem cell (neuroblast) formation

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13
Q

Proneural genes belong to 2 gene families

A
  • Achaete-scutefamily

* Atonal family

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14
Q

Achaete v Atonal

A
  • achaete - present and expressed

* atonal - more imporant for peripheral nervous system

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15
Q

Proneural proteins are

A

bHLH transcription factors

- bind to DNA

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16
Q

Proneural genes are essential for

A

the formation of the nervous system and sensory organ formation

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17
Q

Pronerual mutant

A

2 of proneural genes is effected

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18
Q

Proneural double mutant

A

double number = barely any nervous system

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19
Q

Sensory organs

A

peripheral nervous system
• flies have sensory bristles with a sensory neuron inside
• proneural mutant = no bristles

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20
Q

Specification

A

cells have received the appropriate signals (expression of proneural genes) to become neural cells
• progression along the neural differentiation pathway can still be repressed by other signals

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21
Q

Cometent cells

A

express proneural genes

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22
Q

Specification

A

only 1 cell of the cluster is turned into neural stem cells by neurogenic genes
• some become skin cells (binary decision pathway)
• neurogenic genes see that enough cells left for epidermis
–difficult to restrict to 1 cell to neural stem cell

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23
Q

The antagonistic signal

A

neurogenic genes restrict proneural gene expression to a single cell
• proneural genes - essesntial for neuroblast formation
• neurogenic genes - restrict the number of neuroblasts
–decision bettween between epidermal and neural fate

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24
Q

Mutant neurogenic gene

A

the whole cluster of neural stem cells

  • -> embryos die at embryogenesis
    • lots of nervous no skin in periphery = more sensory bristles
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25
Q

The neurogenic genes that are transmembrane proteins

A

Notch and Delta
• intra, trans, and extra cellular receptors
• communicate so notch receptor and delta ligand come together
• don’t diffuse far so must be neighboring = cluster

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26
Q

There is only 1 neuroblast in a cluster of

A

epidermoblasts

• differ in amount of proneural

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27
Q

Model for interaction of proneural and neurogenic genes

A

only 1 neuroblast in a cluster of epidermoblast
• differ in amount of proneural

• transcription factors switch on Delta ligands and binds to Notch recpetors on neighbor
–> neighbor not able to make neuroblast
• enhancers esp with negative effect on Delta
= FEEDBACK LOOP

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28
Q

Notch signalling inactive

A

proneural gene expression high

–neuroblast

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29
Q

Notch signalling active

A

proneural gene expression low

– epidermoblast

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30
Q

Determination

A
  • no longer responds to Notch signalling

* neuroblasts in fixed positions in neural ectoderm (ventral)

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31
Q

Differentiatin definiton

A

cells have entered the neural differentiation pathway and will become neural cells even int he presence of inhibitory signals
(neurogenic genes)

32
Q

Neuroblasts delaminate from the neuroectoderm region their

A

determination

33
Q

Neuroblasts produce

A

ganglion mother cells (GMC)

• self renew because uneven division

34
Q

Asymmetric cell division =

A

asymmetric division of neural cell fate determinants
• basal complex - inside
• apical complex - outside

35
Q

Par is in all

A

asymmetric

• organize asymmetric division

36
Q

Neural cell fate determinants are localized to the

A

ganglion mother cell
• Miranda = protein binding protein
• mitotic spindle rotates
• 1 cell gets all neural cells, 1 protects

37
Q

Divide asymmetrical –>

A

1 can become another kind of neural cell

38
Q

Neural stem cells only give rise to

A

cells of the neural system

39
Q

Early born neurons form the

A

deepest layers of the central nervous system

40
Q

Neural stem cells

A
  • self-renewing capacity
  • asymmetric cell division
  • pluripotent (capable of giving rise to many different cell types)
41
Q

In all bilaterians the neural progenitors of the central nervous system arise from

A

a single-layered neuroectoderm
• dorsal neural plate –> neural cells only (no epiderm)
(drosophila has a ventral nervous system)

42
Q

Neurulation

A

the neural plate folds into a tube

• in contrast to Drosophila, all cells become neural cells in vertebrates

43
Q

Different types of neural stem cells are generated in the

A

neuroectoderm
neuroepithelium = aka = neuroepithelium
• tube-like structure inside –> nervous system

44
Q

Radial glial cells

A

long, thin processes
• different layers of the brain
– are actually stem cells - give rise to neurons
• radial and glial attached to basal and apical
• basal - not attached to apical

45
Q

Neuroepithial and radial glial cells divide at the

A

apical surface

• interkinetic movements of the nuclei

46
Q

Multiple layers

A
  • brain multi-layered

* spinal cord is not multi-layered

47
Q

Asymmetric division –>

A

neural epithelium looks multi-layered bc nuclei move up and down - in the spinal cord
(everywhere but brain)

(symmetrical –> more stem cells, post mitotic neurons)

48
Q

The post mitotic neurons migrate out of the

A

ventriclar zone

and establish the distinct brain layers

49
Q

The brain has

A

layers
• active migrations if neurons to deeper
–> layers of the brain

50
Q

Despite the different morphologies, conserved genes are expressed during

A

neurogenesis in vertebrates
• proneural genes: eg achaete-scute homologues, members of the Atonal family (Atonal genes, neurogenins)
• neuronic genes: members of the Notch signalling pathway

51
Q

Proneual genes

A
  • achaete-scute homologues

* members of the Atonal family (Atonal genes, neurogenins)

52
Q

Neurogenic genes

A

members of the Notch signalling pathway

53
Q

Members of the Atonal family only after

A

establishment of neural stem cells

54
Q

Neurogenin is expressed in

A

broad stripes in the neural plate of Xenopus

• Neurogenin is in more cells than NeuroD

55
Q

Notch signalling keeps

A

neural precursors in the epithelium

56
Q

The neural plate is all

A

neural cells
• Notch keeps some cells from becoming neural stem cells
• not the case in vertebrates
- need ordered production of neurons bc fate of neurons depends on the time formed

57
Q

Notch signalling has an additional function in vertebrates

A

Notch signalling is necessary for maintaining the neural stem cell pool
• Notch restricts the number of neural stem cells that make neurons

58
Q

Proneural genes have different/additional functions in vertebrates/mammals

A
  • proneural genes promote the generation of neurons
  • also suppresses the formation of glial cells (astrocytes) in mammals
  • required for the delamination and migration of neurons
  • promote cell cycle exit
59
Q

In mammals proneural genes

A

suppress astroglial differentiation and promote neural development

60
Q

Proneural gene function is required for

A

delamination and migration

61
Q

In conrast to Drosophila, proneural genes promote

A

cell cycle exit in vertebrates

62
Q

Proneural and neurogenic genes are conserved in vertebrates and invertebrates, but these genes have

A

partially different/additional functions

63
Q

2 main processes contribute to the generation of neural diversity

A
  • spatial patterning

* temporal regulation of formation

64
Q

In vertebrates - in some cases the identity of a neuron can be influenced

A

a) as it migrates to its final position

b) after innervation of its target tissue

65
Q

Regional subdivision of ventral neuroctoderm

A

A
D V
P

makes a grid of MR IR LR

66
Q

Each neuroblast expresses a different subset of

A

segment polarity and dorso-ventral patterning genes

67
Q

The dorso-ventral patterning genes are

A

conserved in vertebrates

68
Q

Temporal identity genes establish

A

diversity among the progeny of individual neuroblasts

69
Q

Similar to drosophila, there is a strong link between

A

time of formation and neural identity
• neurons are generated first followed by astrocytes and oligodendrocytes
• ventral motorneurons are born first followed by dorsal interneurons
• the ability of the neural stem cells to produce diverse neural cell types becomes restricted over time

–> Notch signalling and additional factors

70
Q

Neurons are generated first followed by

A

astrocytes and oligodendrocytes

71
Q

Ventral motorneurons are born first followed by

A

dorsal interneurons

72
Q

The ability of the neural stem cells to produce diverse neural cell types

A

becomes restricted over time

73
Q

Neuronal subtype identity genes are expressed

A

in response to the spatial and temporal identity cues

74
Q

In all bilaterians, neural stem cells are generated

A

in a single layered neuroepithelium

75
Q

Proneural genes specify

A

neural stem cells

76
Q

Neurogenic genes restrict the number of

A

neural stem cells

77
Q

Spatial and temporal identity mechanisms establish the identity of

A

individual neural stem cells and their progeny

Cell Bio & Developmental Genetics (27 decks)

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