发信人: Marble (小石头哥哥), 信区: Biology
标 题: Re: MCBJC, cellular neurobiology, Mar. 10, 2
发信站: The unknown SPACE (Mon Mar 17 13:49:14 2003), 站内信件

【 在 assasin (冷血---何时能被加热？) 的大作中提到: 】
: Synapse formation
: Questions:
: 1). What’s unique about the methods the authors used to study synaptic site
: specification?
: 2). Why C. elegans is a good organism to address synaptic specificity issue?
: 3). In the syg-1 mutant, the synaptic vesicles are just displaced a little bit
: anterior. Why weren’t they transported to the very anterior termini where the
: HSN neuron synapses on other targets?
: 4). A problem about the paper is that they couldn’t characterize well the
: SYG-1 expression pattern. So, in the functional study, they express syg-1::gfp
: transgene under unc-86 promoter which is much stronger than the syg-1
: promoter. So it’s an overexpression experiment. What flaws could this cause
: to the explanation of SYG-1’s function?


this is very neat work. they used the nematode to address the factors that
are involved in localization and formation of stereotyped synapses. they
found that vulval epithelial cells are involved in the formation of synapses
at the vulva between HSNL and VC neurons.

talking about the general strategy, they first used YFP or GFP directed by
certain promoters that are "specific" to the synapse as markers, and they
demonstrated that they could visualize the formation of synapses near the
vulva. while the system has been established, they set out to address what
types of cells are involved in the synaptogenesis, using a variety of cell-type
specific ablation mutants. this is what i like best about this paper, and in
general, the nematode system; there are so many mutants that have been
generated during the last several decades, and cell lineage for many cells
have been characterized, genome has been sequenced and genomic libraries
are available, etc. once they found that mutant lacking vulva epithelial cells
are defective in the approapriate localization, they carried out a screening
that affect the localization (question, i think they used many already established
mutants, right?), and they identified a mutant syg-1. with genome sequenced,
they found it was the gene SYG-1 by genetic mapping and transformation
rescue (you cannot do this in mouse, think about ppl spending so many years
to functionally clone a "candidate" gene for certain genetic diseases). this
gene, syg-1, encodes a 727 aa novel transmembrane protein in the IG
superfamily. then they demonstrated the cell autonomy of SYG-1 in HSNL
by directing its expression in the HSN neurons to rescue the defective
synaptogenesis in syg-1 mutant (question,at first i thought that SYG-1 is
localized to the epithelial cells, now it turns out that it might be a receptor
on the HSN neurons. so what are the signals from the epithilial cells?)
the problem to study SYG-1 is that its expression is very weak, and they
had to use another stronger promoter. this might lead to unexpected expression
in other regions of the worm (they used unc86::SYG1::GFP). actually, it is
clear that they get specific expression pattern, while the pattern is different
from another transgene unc86::SNB, which suggests the specificity for the
SYG1 promoter. virtually, i think they should still have some other mutants
that they have not published (maybe Shen takes it as his faculty research).
i would focus on the epethilial cells and try to find the signaling pathways
that are involved. for example, while RNAi has been successful with the worm,
i would do a tissue-type specific RNAi using epethilial cell type specific
promoter, and then characterize the mutants that are defective in the
synaptogenesis of HSN/VC neurons near the vulva.

very nice job, particularly when you think about the genetics they have used
in the study.












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