Module 1 Lecture 6: Synaptogenesis

Question 1

starburst amacrine function

Answer 1

detecting direction of motion

Question 2

characteristics of fly Dscam1isoforms

Answer 2

• homophilic
• 4 alternatively spliced exons; 3 are for the ectodomain
• 19008 ectodomain isoforms possible

Question 3

what happens if dendritic arborization neurons don’t have Dscam1

Answer 3

spread out process of dendritic arborization (da) neurons collapse and cross over

Question 4

is Dscam1 splicing selective?

Answer 4

no, nearly random

Question 5

how is the Dscam1 identity developed

Answer 5

each neuron expresses several to a few tens of different isoforms

Question 6

what does homophilic binding result in in Dscam1

Answer 6

repulsion

Question 7

how is self-avoidance designed in Dscam1

Answer 7

each neuron can only bind its own set of Dscam1 isoforms

Question 8

what results from reduced Dscam1 diversity (by overexpressing 1 isoform)

Answer 8

2 different da neurons that normally ignore each other now avoid crossing

Question 9

how is ectodomain diversity in vertebrate Protocadherin clusters achieved

Answer 9

through alternative transcription start sites (contrast to fly Dscam1)
- each isoform is homophilic

Question 10

function of domains EC2 and EC3 in Protocadherin clusters

Answer 10

mediate the specificity of homophilic binding

Question 11

similarities between Protocadherin EC1 and Dscam Ig2

Answer 11

domains have similar folds

Question 12

the question of synaptic specificity

Answer 12

after having arrived at the correct target area and layer, how do neurons choose the correct synaptic partners from among many contact partners?

Question 13

example of stringent specificity

Answer 13

C3 neurons in fly visual system contacts both Tm1 and Tm2 neurons but only makes synapses with Tm1

Question 14

biased specificity example

Answer 14

an On-SAC in the mouse retina has similar amount of contact with N- and V- ooDSGCs but makes more synapses with the V-type

Question 15

types of synaptic specificity

Answer 15

adhesion, repulsion, elimination, and subcellular localization

Question 16

first hypothesis for synaptic specificity

Answer 16

sequential: partner choice, then synapse formation

Question 17

second hypothesis for synaptic specificity

Answer 17

package deal: combination of same cell adhesion molecules on pre- and post-synaptic cell mediate both partner choice and synapse formation

Question 18

third hypothesis for synaptic specificity

Answer 18

make, then break: non-specific (promiscuous) synapses selectively eliminated after partner choice is made

Question 19

why are in vitro studies of neurons less relevant to in vivo studies

Answer 19

neurons are synapse-happy and synapse-willing; they will readily make synapses with most sticky surfaces

Question 20

what happens after neurogenesis and neuronal migration

Answer 20

axon guidance and dendritic arborization

Question 21

what happens after axon guidance and dendritic arborization

Answer 21

nascent synapse formation

Question 22

what happens after nascent synapse formation

Answer 22

either mature synapses or synapse elimination

Question 23

what happens after mature synapses form

Answer 23

synapse elimination

Question 24

what happens after synapse elimination

Answer 24

nascent synapse formation

Question 25

first action from nascent synapses

Answer 25

engaging trans-cellular SAM complexes - eg FLRTs/Teneurins <--> Lphns

Question 26

second action from nascent synapses

Answer 26

pre- and postsynaptic intracellular signals

Question 27

third action from nascent synapses

Answer 27

initial synapse assembly

Question 28

first action from mature synapses

Answer 28

signaling via diverse trans-synaptic SAM complexes - eg Neurexins <--> Nlgns and Cblns/GluDs

Question 29

second action from mature synapses

Answer 29

pre- and postsynaptic protein activation (eg CASK)

Question 30

third action from mature synapses

Answer 30

specification of synapse properties

Question 31

first action of synapse elimination

Answer 31

disassembly of SAM complexes

Question 32

second action of synapse elimination

Answer 32

pre- and postsynaptic disruption signals (unknown)

Question 33

third action of synapse elimination

Answer 33

synapse elimination

Question 34

what happens if you disrupt gene/process involved in earlier steps in synapse formation

Answer 34

will not get to synapse formation

Question 35

what happens if you disrupt a gene/process involved in later steps of synapse development

Answer 35

may look like synapse formation was affected

Question 36

what do axons from CA3 region of the hippocampus form synapses with

Answer 36

CA1 pyramidal neurons in two of three possible layers (stratum oriens and s. radiatum and not s. lacunosum-moleculare

Question 37

where are Lphn2 and Lphn3 targeted

Answer 37

to distinct and non-overlapping regions of the post-synaptic CA1 neuron dendrites

Question 38

what does Lphn3 mediated synapse formation require

Answer 38

simultaneous binding of two pre-synaptic cell surface molecules

Question 39

how is specificity of synapse formation achieved?

Answer 39

specific compartmentalization of Lphn3 and co-incidence detection of correct pre-synaptic axons

Question 40

what is Lphn3 necessary for

Answer 40

- formation of subset of excitatory synapses in cultured hippocampal neurons - synapse formation in s. oriens and s. radiatum but not s. lacunosum-moleculare - CA1 excitation by the Schaffer collateral fibers

Question 41

what happens without Lph3

Answer 41

- loss in excitatory post-synapses (spines) - in vivo hippocampal neuron excitatory synapse function compromised - number of pre-synaptic CA3 neurons (origin of Schaffer collaterals) drop significantly without Lphn3

Question 42

characteristic of Lphn3 4A mutatnt

Answer 42

cannot bind FLRT

Question 43

characteristic of delta Lec

Answer 43

cannot bind Teneurin

Question 44

can binding mutants rescue loss of excitatory synapses

Answer 44

no

Question 45

what does Lphn3 dependent synapse formation in cultured hippocampal neurons require

Answer 45

both teneurin binding and FLRT binding by Lphn3

Question 46

can binding mutants rescue loss of excitatory synapses

Answer 46

no

Question 47

what is necessary for excitatory synapse function

Answer 47

Lphn ability to bind both pre-synaptic partners

Question 48

what are Schaffer collaterals

Answer 48

axons from CA3

Question 49

under what conditions do Schaffer collaterals come through

Answer 49

where Lphn3 is expressed

Question 50

what happens where Lphn2 is expressed

Answer 50

axons from the entorhinal cortex come through (perforant pathway)

Question 51

significance of Lphn3 capable of binding both pre-synaptic partners

Answer 51

is sufficient to rescue CA1 excitation in response to Schaffer collateral stimulation

Question 52

can Lphn2 expression rescue Lphn3-loss dependent increase in CA1 excitation in response to Schaffer collateral stimulation

Answer 52

no

Question 53

is Lphn3 necessary for CA1 excitation in response to perforant pathway stimulation

Answer 53

no

Question 54

rabies virus function

Answer 54

spreads from post-synaptic to pre-synaptic neuron; used for retrograde tracing

Question 55

first step of rabies virus experiment

Answer 55

introduce Cre to delete Lphn3

Question 56

second step of rabies virus experiment

Answer 56

introduce rescue constructs (eg WT or mutant Lphn3)

Question 57

third step of rabies virus experiment

Answer 57

set up retrograde tracing with rabies virus, engineered to 'jump' only 1 synapse (replication-deficient) and to carry GFP for marking the infected pre-synaptic neurons

Question 58

end result of the rabies virus experiment

Answer 58

Cre (which deletes the Lpn3 cKO allele), GFP, mCherry (red)

Question 59

what do pre-synaptic neurons express in the rabies virus experiment

Answer 59

GFP

Question 60

what is not affected by loss of Lphn3

Answer 60

number of pre-synaptic entorhinal cortex neurons (perforant pathway)

Question 61

significance of post-synaptic expression of Lphn3 in CA1 neurons

Answer 61

necessary and sufficient to form synapses specifically with Schaffer collaterals from CA3 neurons