MCDB 423 Lecture 33: Lecture 33
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Department
Molecular, Cellular and Developmental Biology
Course
MCDB 423
Professor
John Kuwada
Semester
Winter

Description
Lecture 33 Slide 6 Lrp4 may serve as a stop signal for motor growth cones. We learned before that lrp4 is required receptor for agrin and therefore is required for synaptic localization of AChR -Also involved in receptor complex with musk This paper starts out with the lrp4 knockout -You don’t get clustering of AChR -If you look at the motor terminals, they extend much further from the nerve than normal in the knockout -This suggests the possibility that lrp4 may be a stop signal slide 7 They took a mouse with HB9 (transcriptional factor expressed by all motor neurons) that is driving the expression of GFP -So all motor neurons will be green in this mouse Take the motor neurons, grow in culture and because they’re expressing GFP, you can see the axons -Then culture the motor neurons with myotubes or other cells that may be expressing lrp4 or something else If you do co-culture with myotubes, you can see that there is accumulation of AChR (used by alpha-boto-toxin) -If you label with synapsin, it’s the same as the AChR This demonstrates that this system develops normally This assay is used to test if lrp4 might be a factor that can affect the differentiation of the pre- synaptic motor terminals Slide 8 3T3 and Hek293 cells were transfected with Lrp4 to test whether Lrp4 induce clustering of synaptic vesicles Take these mammalian cells lines -3t3 cells are grown with motor neurons and you can see that they are expressing mcherry and the axons do contact them but there’s no synasin meaning none of these axons have an aggregation of synaptic vesicles (control experiment) -Shows that 3t3 cells don’t have the ability to induce the clustering of synaptic vesicles and motor neurons However, if those 3t3 cells are expressing lrp4, what you see is if you label for synapsin, you get clusters suggesting there’s clusters of synaptic vesicles that are co-extensive with the HB9:GFP meaning they’re motor neuron derived clusters This is a primary evidence that lrp4 has a retrograde signaling that can induce pre-synaptic terminal differentiation Slide 10 LDLa: low density lipoprotein receptor class A domain Since LDLa  bind LDL (low density lipoprotein) maybe involved in signaling to motor terminals to differentiate. Fc: constant region of IgG  dimerization Recall Lrp4 dimerizes Instead of expressing lrp4 in cells, they put a part of lrp4 onto a microsphere -The most peripheral part of the receptor
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