Lecture 10 (5a) - Neural Stem Cells in Vertebrates and Invertebrates Flashcards Preview

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Flashcards in Lecture 10 (5a) - Neural Stem Cells in Vertebrates and Invertebrates Deck (44)
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1

In Drosophila neuroblasts segregate from the

neuroectoderm and the neuroblast progeny are passively dispaced towards interior
• stem cells divide symmetrically to make more (self-renewing)
• asymmetrically --> diff cell fates

2

The postmitotic neurons migrate

out of the ventricular zone and establish the distinct brain layers

3

Despite the different morphologies, conserved genes

are expressed during neurogenesis in vertebrates
• proneural genes
achaete-scute homologues
atonal family
• neurogenic genes - members of the notch signalling pathway

4

All cells express

proneural genes
but notch represses
• determine how many stem cells are formed at 1 time

5

Neurogenin is expressed

in broad stripes in the neural plate of xenopus
• neural plate (outside) folds in and makes neural tube

6

Notch signalling keeps

neural precursor in the epithelium
• Notch keeps neural stem cells pool - ensures symmetric division
• no Notch --> premature divides asymmetrically --> no stem cells
• only fate of newly born neurons (embryonic lethal)

7

Notch signalling has an additional function in vertebrates

Notch signalling is necessary for maintaining the neural stem cell pool

8

Proneural genes have different/additional functions in vertebrates

• proneural genes promote the generation of neurons but also SUPPRESS THE FORMATION OF GLIAL CELLS (astrocytes) in mammals
• proneural genes are required for the DELAMINATION and MIGRATION of neurons
• proneural genes promote CELL CYCLE EXIT

9

In mammals, proneural genes suppress

astroglial differentiation and
promote neural development

10

Proneural gene function in vertebrates is required for

delamination and migration

11

In contrast to Drosophila, proneural genes promote

cell cycle in vertebrates
• Drosophila = no migration

12

Proneural and neurogenic gene are

conserved in vertebrates and invertebrates
• but these genes have partially different/additional functions
(homologs)

13

Neurogenesis can be subdivided into 4 processes

1. generation of neural stem cells
2. establishment o neural precursor identity
3. differentiation of neural precursors
4. establishment of neuronal networks

14

2 main processes contribute to the generation of neural diversity (mainly in invertebrates)

• spatial patterning (info from place)
• temporal regulation of formation (timing)

15

In vertebrates, the identity of a neuron can be influenced

• as it migrates to its final position
• after innervation of its target tissue

16

Regional identity genes

establish neuroblast diversity in Drosophila
• segment polarity for ant/post identity
• stripes in each segment
• remain expressed in neuroectoderm and later specifically in neuroblasts
• longitudinal overlapping --> grid pattern (dorso/ventral)
• each proneural cluster gets positional identity

17

The expression profiles of the neuroblasts determine

the identity o their progeny
• motor and interneurons need even-skipped
• PCC and ACC - longitudinal, motor neurons
• PLACE AFFECTS PROGENY

18

Gray = neuroblasts express

Msh
• no Msh in lateral
(not expressed throughout neurogenesis - only 2 divisions then off)

19

Msh expressed in

• lateral domain of ventral ectoderm in spider
• continuous lateral domain in the millipede
• temporal and spatial variations in arthropods

20

The early motor and interneuronal marker eve and islet are expressed in

subsets of NPGs in the spider

21

Msh regulates

islet expression in the lateral ectoderm
• regional identity genes regulate neuronal sub-type identity similar to Drosophila

• region determines fate
• drosophila gene regulation doesn't transfer to explain it in other organisms

22

Evolutionary changes in the regulation of

neuronal sub-type specific genes in arthropods

23

Msh =

Msx in vertebrates

24

Temporal identity
The dorso-ventral patterning genes are

conserved in vertebrates

25

The number of divisions and type of progeny produced is

pre-planned

26

Temporal identity genes establish

diversity among the progeny of individual neuroblasts
• color = same neuroblast, delaminates
• divide and change to expression of another gene
• later expression --> dies

27

Temporal identity in Drosophila

all segments at the same time
• growth then segmentation in others

28

The expression of temporal genes leads to

the formation of distinct neuronal subtypes in neuroblasts 5-6T
• NB 5-6T produces a mixed lineage of 20 cells
• the 4 last born cells are interneurons expressing Apterous (LIM-homeodomain) transcription factor
• the 4 Ap neurons can be further subdivided into 3 different neuronal subtypes

29

Similar to Drosophila, there is a strong link between

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

30

Neuronal subtype identity genes are expressed in response

to the spatial and temporal identity cues
• LIM proteins regulate subtype specificity in motorneurons