We have created a fusion protein between VAMP, an integral synaptic vesicle membrane protein, and GFP, and have an integrated array (jsIs1) of it in nematodes. jsIs1 worms show bright fluorescence in the nerve ring, ventral cord, and dorsal cord. Sublateral bundles are visible as chains of discrete bright spots. Commissures and the amphid dendritic bundles are not normally visible. Some neuronal cell bodies fluoresce faintly. Several lines of evidence imply that this fluorescence is primarily due to VAMP-GFP localizing to synaptic vesicles. First, VAMP antibody staining in wildtype worms shows that VAMP-GFP fluorescence parallels normal VAMP localization. Second, in
unc-104; jsIs1 animals, fluorescence is concentrated in cell bodies and absent from the dorsal cord entirely. This suggests that axonal membrane does not contain significant amounts of VAMP-GFP. Third, in
unc-5; jsIs1 animals, patchy fluorescence is seen in lateral and sublateral positions, where ectopic synapses have been seen by Hedgecock, et. al. Fourth, in strains where VAMP-GFP is expressed only in specific subclasses of neurons using neuronal specific promoters such as
mec-7, we see fluorescence where synapses have been described by the ultrastructural studies of White, et. al. We have performed a pilot screen for synaptogenesis mutants using jsIs1 and have isolated mutants with axonal elongation or migration problems, with accumulation of label in cell bodies, and with inappropriate patches of fluorescence. To increase our ability to see subtle changes in synaptic label, we are developing several VAMP-GFP constructs under control of promoters for specific neuronal subtypes. We are also exploring the plasticity properties of the nervous system using ablation studies in combination with VAMP-GFP.