Lecture 11 (5b) - Neurogenesis in Invertebrates and Axonal Pathfinding

Question 1

Neural stem cells have evolved

Answer 1

independently in arthropods and vertebrates

Question 2

Insect and vertebrate neural stem cell development and regulation are

Answer 2

different
Insects
• neural stem cell proliferation
• asymmetric division in epithelium
• formation of postmitotic neurons

Vertebrates
• neuroblast formation
• neuroblast delamination
• formation of postmitotic neurons

Question 3

Similar to vertebrate neural stem cells, Daphnia magna neuroblasts

Answer 3

remain in the epithelium

Question 4

Morphology of Daphnia magna embryo during neurogenesis

Answer 4

neuroblast formation = smooth w/ slits

differentiation of neurons = slits bump out, formation of axonal tracts

Question 5

Homologues of Drosophila neural genes are

Answer 5

expressed in Daphnia magna neurogenesis

Question 6

In Daphnia, no proneural cluster –>

Answer 6

ring of neuroblasts

Drosophila has proneural clusters so different regions w/ clusters

Question 7

sna –> ASH in

Answer 7

both Daphnia and Drosophila

Question 8

ASH not that important in

Answer 8

neuroblast formation

Question 9

The differences in the morphology of neuroblast formation are reflected in the

Answer 9

gene expression patterns

Question 10

Vertebrates show a similar sequence of gene expression

Answer 10

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

Question 11

Notch keeps cells

Answer 11

in transition phase so there’s enough neural stem cells

Question 12

Most neuroblasts do not generate GMCs before

Answer 12

NS4 = ~ 10 hours delay

• most neuroblasts form very early (NS2) but don’t form GMC until late

Question 13

The members of Notch signalling pathway are expressed in

Answer 13

neuroblasts

• Notch also needed in limb development

Question 14

Inactivation of Notch signalling leads to

Answer 14

over-expression of Dam sna and Dam pros in al cells of the ventral neuroectoderm
• DAPT inhibits Notch

Question 15

Inactivation of Notch signalling leads to

Answer 15

premature generation of GMCs
• immediately divide GMCs –> neurons early w/o Notch
• inactivation of Notch signalling also leads to ectopic formation of neuroblasts

Question 16

GMC

Answer 16

ganglion mother cell

Question 17

Notch signalling is required for

Answer 17

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)

Question 18

Model for neuroblast regulation in D. magna

Answer 18

• neuroblast generation and division (sna+)
• transition (n+, DI+, Hes+, ASH+, sna+)
• GMC production (DI++, pros+, ASH++, sna+)

Question 19

Neurogenesis can be subdivided into 4 processes

Answer 19

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

Question 20

The generation of neuronal processes occurs at

Answer 20

the growth cone

• filopodia of actin

Question 21

What is the function of neuronal growth cones?

Answer 21

1. growth cones navigate the developing axon/dendrite through the developing embryo towards the target cell
2. Growth cones form the developing axon/dendrite
3. Growth cones form the pre- and postsynaptic structure

Question 22

Growth cones contain

Answer 22

actin and microtubuli
•  actin make filopodia
•  p = peripheral
•  c = core regions
•  n = neurite

Question 23

Filopodia

Answer 23

touch/sense signal, stabilize

• made of actin

Question 24

The different structures of the peripheral domain of the growth cones

Answer 24

philopodia –> lamellipodium