Synaptogenesis Flashcards
Briefly describe the important steps leading up to synaptic vesicle release
- Depolarization reaches synaptic bouton: Na largely mediates this
- AP reaches the Voltage-gated Ca channels
- Ca enters the cell
- Ca acts on vesicles causing them to fuse to the membrane
- Release of NT into the synaptic cleft
What is laminar specificity?
The specificity achieved by neurons projecting into different layers of a target tissue
e.g. spinal cord, IPL of the retina
How many kinds of bipolar cells are there?
~12
How many kinds of amacrine cells are there in the retina?
~19
In the IPL of the retina, what kinds of cell surface receptors are thought to mediate synaptic target specificity? (3)
Dscam, semaphorins, protocadherins
What molecule likely mediates 3o branch self avoidance?
mig-14, a homolog of wntless
When the mig-14/wntless pathway is activated, what occurs?
F-actin depolymerization causing retraction of 3o dendrites
Why are calcium indicator experiments useful for examining the formation of synapses?
Can examine where activity is (calcium = proxy for NT activity) particularly in filopodia to examine which projections make prolonged contact with synaptic targets
Explain what is happening in this graph
When filopodia grow and make contact with axons, the number of calcium transients increases to form a connection
Explain the takeaway from this image
When filopodia make stable contacts with an axon, calcium transients increase and synapses are more likely to form
Based on this information, what is a feasible hypothesis for what is happening when connections are being made?
Some kind of protein or signaling factor must be acting upstream of calcium influx to establish a connection between an axon and its synaptic target
Since filopodia stability precedes synapse formation, what does this suggest about the mechanisms which control synapse formation?
Must be regulated by cytoskeletal processes
What kind of staining is Cajal credited with inventing?
Golgi staining
Explain golgi staining
Stains the golgi bodies and is pretty good at targeting neurons specifically, although it tends to only target every few neurons not all of them
what kinds of neurons make connections with the cell bodies of purkinje cells?
Basket cells
Describe the axons of a basket cell and how they synapse to purkinje cells
Axons are all gathered around (and synapse to) the soma of purkinje cells and around the upper axon of purkinje cells
Describe how the specificity of basket cells synapsing to purkinje somas/upper axons is established
Neurofascin gradient around the soma which attracts axons, then axons attach to ankyrin G repeats around the AIS
AnkyrinG is a binding partner to (2)
Voltage-gated sodium channels and Neurofascin
What happens in purkinje neurons where ankyrinG is knocked out?
Axons of basket cells no longer preferentially synapse to the AIS
Name 4 levels by which specificity in synaptic target can be established
Laminar, cellular, subcellular, synapse-type
What is an example of types of synaptic connections which are mediated by synapse type?
Neurexin/neuroligin complex
Describe how prevalent the neurexin/neuroligin complex is
Expressed by most neurons
Describe which synaptic membrane the neurexin/neuroligin are present on
Neurexin: presyn
Neuroligin: postsyn
Describe how diversity/complexity is established among neuroligin/neurexin complexes
Neurexin on the presyn membrane has an alternatively spliced extracellular domain which conveys specificity
Neurexin/neuroligin mediates (heterotypic/homotypic) interactions
Homotypic
Alternative splicing aside, what are the 2 kinds of neurexin?
Alpha (long) and beta (short)
What is the proposed difference between alpha and beta neurexin?
May regulate GABAergic/glutamatergic synapse formation
Describe what SS#4 is with respect to neurexin
It is a 30 aa splice variant which the protein can be made with or without
When the SS#4 variant of neurexin is present, the protein can interact with…
NMDR, a glutamate receptor
Without the SS#4 variant, neurexin cannot interact with (1) but it can interact with (2, 3)
- Neuroligin
2/3. CAN interact with NMDR and AMPA glutamate receptors
The working hypothesis about neurexin complexes suggest that different neurexin ligands organize different…
Types of synapses
Name 9 kinds of molecules present on the postsyn neuron membrane which could be mediating synapse specificity
Neuroligins
Cadherins
AnkyrinG/Neurofascin
SynCAM
Protocadherins
TrkB
LAR-RPTP
Dasm1
NCAM
Name 5 kinds of molecules present on the presyn neuron membrane which could be mediating synapse specificity
alpha/beta neuroexins
SynCAM
Protocadherins
Cadherins
CPG14
Name 6 kinds of molecules present in the soluble/extracellular synaptic cleft which could be mediating synapse specificity
Laminin
Versican
Thrombospondin
FGF22
Heparin sulfate
Proteoglycans
Why is the neuromuscular junction a good model for studying the development of the axon-dendrite synapse? (3)
Large size
Accessible
Simple organization
Dendritic filopodia and dendritic spine motility is regulated in part by these two molecules (2) that act on…
TrkB and EphB2, act on F-actin dynamics
What ligand acts on muscle-specific tyrosine kinase receptors (MUSK) at the NMJ?
Agrin
Activation of MUSK stimulates…
Clustering of acetylcholine receptors
Monomers of MUSK are called…
LRP4
Within the NMJ, the active zones surrounding a muscle fiber are arranged in…
An outside-in manner
Adjacent to the active zone, there is the (1) zone
Peri-active
What is a key receptor on the postsynaptic side of the peri-active zone?
Shaker
What binds to shaker?
Dlg - scaffold protein which arranges cells close together so that a correct synapse can occur
Lining the inside of the postsynaptic membrane are the important cytoskeletal proteins… (2)
alpha and beta spectrin
Describe the importance of beta spectrin
Ensure proper synaptic proteins are localized to a region where synaptic activity is occurring to ensure exposure to neurotransmitter – helps link proteins to the cytoskeleton
The Gal4-UAS system is derived from…
Yeast
Describe the Gal4-UAS system briefly
Gal4 can be placed downstream of a promoter, and when transcribed/translated will bind to UAS to activate a gene which is downstream of UAS, this could be a gain/loss of function, or GFP for example
In the Gal4 system, there is usually a cross between X-Gal4 and UAS-Y, where X and Y are target genes. Which of these two lines is the “driver” line?
X-Gal4
What is the primary utility of the Gal4 system
It is an inducible model: can be used for conditional knockouts, etc.
