Functional analysis of dynamin isoforms in Drosophila melanogaster

Dynamin and dynamin-like proteins are required for endocytosis, synaptic ve sicle recycling and membrane trafficking. From the shibire locus in Drosoph ila melanogaster, six different isoforms of dynamin are generated by altern ative splicing. However, the roles of the individual isoforms in cellular p rocesses are unknown. To investigate functional differences among the dynam in isoforms, transgenic lines were generated that individually expressed ea ch of 3 different isoforms under UAS(GAL4) control. The expression of the i soforms was controlled by neural promoter (elav)-driven GAL4, or by a shibi re-promoter driven GAL4 transgene. Reporter gene expression indicated that the shi promoter is active during embryogenesis, and in larvae, pupae, and adults in a pattern consistent with normal dynamin expression. To assay for the ability of dynamin isoforms to function in vivo, the isoforms expresse d via these GAL4 drivers were tested for the ability to rescue shibire phen otypes. When expressed at very high levels, all individual isoforms tested rescued the temperature-sensitive paralytic phenotype of shi(ts2) flies; ho wever, this rescue was partial, suggesting that no single tested isoform is sufficient for synaptic vesicle recycling in vivo. When tested for ability to rescue lethality induced by heat-pulsing larvae during development, shi - promoter driven expression of individual isoforms conferred significant r esistance to heat treatment during larval development. However, all 3 isofo rms were unable to rescue the lethality of shi(12-12B) mutants which are se verely hypomorphic (or null) for shibire function. Taken together, these ob servations suggest that individual shibire isoforms have specific molecular activities in vivo.