Lecture 11 (5b) - Neurogenesis in Invertebrates and Axonal Pathfinding Flashcards
(24 cards)
Neural stem cells have evolved
independently in arthropods and vertebrates
Insect and vertebrate neural stem cell development and regulation are
different Insects • neural stem cell proliferation • asymmetric division in epithelium • formation of postmitotic neurons
Vertebrates
• neuroblast formation
• neuroblast delamination
• formation of postmitotic neurons
Similar to vertebrate neural stem cells, Daphnia magna neuroblasts
remain in the epithelium
Morphology of Daphnia magna embryo during neurogenesis
neuroblast formation = smooth w/ slits
differentiation of neurons = slits bump out, formation of axonal tracts
Homologues of Drosophila neural genes are
expressed in Daphnia magna neurogenesis
In Daphnia, no proneural cluster –>
ring of neuroblasts
Drosophila has proneural clusters so different regions w/ clusters
sna –> ASH in
both Daphnia and Drosophila
ASH not that important in
neuroblast formation
The differences in the morphology of neuroblast formation are reflected in the
gene expression patterns
Vertebrates show a similar sequence of gene expression
neural cell formation –>
MASH, Notch signalling –>
MASH, Prox1
in vertebrates, ASH not needed for neural stem cells
MASH switches on Prox1
Prox1 for asymmetrical divisions –> neurons
Notch keeps cells
in transition phase so there’s enough neural stem cells
Most neuroblasts do not generate GMCs before
NS4 = ~ 10 hours delay
• most neuroblasts form very early (NS2) but don’t form GMC until late
The members of Notch signalling pathway are expressed in
neuroblasts
• Notch also needed in limb development
Inactivation of Notch signalling leads to
over-expression of Dam sna and Dam pros in al cells of the ventral neuroectoderm
• DAPT inhibits Notch
Inactivation of Notch signalling leads to
premature generation of GMCs
• immediately divide GMCs –> neurons early w/o Notch
• inactivation of Notch signalling also leads to ectopic formation of neuroblasts
GMC
ganglion mother cell
Notch signalling is required for
binary cell fate decisions in crustaceans
• the restriction of neuroblast formation to the ring-like domain results in a limited number of neuroblasts (typical feature of euarthropods)
• Notch needed in Daphnia
keeping neuroblasts silent (no division)
Model for neuroblast regulation in D. magna
- neuroblast generation and division (sna+)
- transition (n+, DI+, Hes+, ASH+, sna+)
- GMC production (DI++, pros+, ASH++, sna+)
Neurogenesis can be subdivided into 4 processes
- generation of neural precursors
- establishment of neural precursor identity
- differentiation of neural precursors
- establishment of neuronal networks
The generation of neuronal processes occurs at
the growth cone
• filopodia of actin
What is the function of neuronal growth cones?
- growth cones navigate the developing axon/dendrite through the developing embryo towards the target cell
- Growth cones form the developing axon/dendrite
- Growth cones form the pre- and postsynaptic structure
Growth cones contain
actin and microtubuli • actin make filopodia • p = peripheral • c = core regions • n = neurite
Filopodia
touch/sense signal, stabilize
• made of actin
The different structures of the peripheral domain of the growth cones
philopodia –> lamellipodium
