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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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


The postmitotic neurons migrate

out of the ventricular zone and establish the distinct brain layers


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


All cells express

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


Neurogenin is expressed

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


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)


Notch signalling has an additional function in vertebrates

Notch signalling is necessary for maintaining the neural stem cell pool


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


In mammals, proneural genes suppress

astroglial differentiation and
promote neural development


Proneural gene function in vertebrates is required for

delamination and migration


In contrast to Drosophila, proneural genes promote

cell cycle in vertebrates
• Drosophila = no migration


Proneural and neurogenic gene are

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


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


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

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


In vertebrates, the identity of a neuron can be influenced

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


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


The expression profiles of the neuroblasts determine

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


Gray = neuroblasts express

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


Msh expressed in

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


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

subsets of NPGs in the spider


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


Evolutionary changes in the regulation of

neuronal sub-type specific genes in arthropods


Msh =

Msx in vertebrates


Temporal identity
The dorso-ventral patterning genes are

conserved in vertebrates


The number of divisions and type of progeny produced is



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


Temporal identity in Drosophila

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


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


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


Neuronal subtype identity genes are expressed in response

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