Worm Breeder's Gazette 14(5): 40 (February 1, 1997)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
329 Sinsheimer Laboratories, Dept. of Biology, University of California, Santa Cruz, CA 95064 (e-mail: firstname.lastname@example.org)
Long-term synaptic plasticity is widely observed in diverse organisms from insects to mammals. It often involves two aspects of concurrent changes in the neurons: the structural change and the change in synaptic strength. In C. elegans, one example of such neuronal plasticity is the synaptic rewiring of the DD motor neurons. DD motor neurons are GABAergic inhibitory neurons born during embryogenesis. In L1 larval stage, DDs receive synaptic inputs from DA and DB motor neurons on the dorsal side and innervate ventral body wall muscles. However in older larvae and adults, DD neurons receive inputs from VA and VB neurons on the ventral side and form NMJs on the dorsal side. The original DD neuron connectivity is replaced by another class of GABAergic neurons, VDs, which are generated by postembryonic cell division (l). Little is known about either the detailed process of the synaptic rewiring of DD neurons or the molecular mechanism underlying such a synaptic polarity switch. We are interested in elucidating the molecular mechanisms regulating the remodeling of DD synapses. We are using a synapse specific GFP marker to visualize the synaptic rewiring (2), and to perform a genetic screen for genes regulating the structural and synaptic changes of DD neurons during the rewiring. The GFP marker, Punc-25-VAMP-GFP, is specifically expressed in the pre-synaptic zones of DD and VD neurons (together called type D neurons). VAMP-GFP chimeric protein is localized to the presynaptic zone of neurons (3). The promoter of the unc-25 gene, which encodes GABA biosynthetic enzyme glutamic acid decarboxylase, is used to specifically activate the expression of VAMP-GFP in DD neurons in L1 stage and DD&VD neurons in L2 to adult stages. In this screen we are recovering mutant animals showing any abnormal GFP expression patterns in the D neurons so that a wide spectrum of genes involved in the synapse formation of the D neurons can be isolated. But the further characterization will be focused on those disrupting the DD neuron synaptic rewiring (most likely to be the ones with little or abnormal GFP expression in the dorsal cord from L2 stage onward). So far we have screened 8,000 haploid genomes using EMS as the mutagen. New alleles of known genes required for axonal growth and synaptic formation, such as unc-5, unc-6, unc-11, unc-30, unc-33, unc-51, unc-76, and unc-104 have been isolated. The new allele (ul9) of unc-104 gene, which encodes the kinesin heavy chain and is essential for vesicle transport, is particularly interesting since the mutant animals show very little abnormality in movement. The GFP expression pattern in ju19 indicates that this mutant is able to make nearly normal synapses in the ventral cord, but fail to make synapses in the dorsal code. This suggests that ju19 may be defective in long-distance vesicle transport. More than 100 lethal/sterile mutants, most of which are defective in postembryonic cell division (thus fail to generate VD neurons) were also isolated from the screen. Intriguingly we have isolated a number of viable mutants with severely disrupted GFP expression pattern in either the DD or VD neurons (or in both), yet only subtle abnormality in locomotion. Because of the subtle visible phenotype of these mutants, they might represent new genes which are essential for the normal D neuron synaptic formation, but fail to be uncovered by previous unc screens. We are in the process of characterizing and mapping these mutations. Ref: 1) White JG, Albertson DG and Anness M. Nature 271: 764-766, 1978 2) Jin YS and Horvitz HR. 1995 Worm Meeting Abstract: 291. 3) Nonet ML WBG 13(5): 40, 1995