2000 West Coast Worm Meeting abstract 88
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Department of Anatomy, UCSF, San Francisco, CA 94143
Axons in developing organisms must migrate and extend long distances in order to synapse onto their proper targets. Little is known about how extracellular guidance cues elicit the changes in cytoskeletal dynamics that drive axon outgrowth. In order to understand the factors that control the development of the HSN motorneuron, we are undertaking an observational approach. We are utilizing two-photon microscopy to analyze the trajectory of HSN as it grows ventrally in late L2/early L3 stage worms. Using worms expressing GFP under the unc-86 promoter, we are able to visualize HSN during the course of its outgrowth.
Preliminary imaging indicates that HSN initially extends filopodia in all directions from its cell body, but that only those filopodia facing the ventral side persist. Eventually these filopodia develop into a large lamellopod that extends ventrally and stalls at the ventral muscle barrier. A few processes protrude through the body wall muscle attachment sites, as seen in VD and DD motorneuron growth through the dorsal muscle attachment sites.1 Although multiple processes extend toward the ventral nerve cord, only one is stabilized and develops into the axon.
We plan to characterize HSN outgrowth over the course of its development. With this information, we can analyze the HSN axon in mutant worms known to have defects in ventral growth. In particular, we will examine worms containing mutations in the extracellular guidance cues to which HSN responds as well as in cytoplasmic proteins thought to participate in the regulation of cytoskeletal dynamics. In addition, we plan to label the actin and microtubule cytoskeletons and visualize their dynamics during HSN outgrowth. This approach will allow us to elucidate the roles of particular proteins in the process of HSN outgrowth.
1. Knobel KM, Jorgensen EM, Bastiani MJ. Development. 1999 Oct;126(20):4489-98.