A novel mutation in the Drosophila slingshot (ssh) gene identifies a requirement for its function in the maintenance of synapse morphology. Jason E. Duncan, Kayla Johnson. Department of Biology, Willamette University, Salem, OR.

   Maintenance of the cytoskeleton is essential for normal function of nerve cells. We have identified a mutation in slingshot (ssh), a gene that encodes a phosphatase that dephosphorylates the actin-depolymerizing factor (ADF)/cofilin protein, which regulates microfilament dynamics. The ssh^WU6 allele is the result of a missense mutation that converts the amino acid Glycine²³³ (GGA) to Glutamic Acid²³³ (GAA). Glycine²³³ is an amino acid that is invariant across the eumetazoa in the highly conserved cofilin binding domain of the ssh protein. Third instar ssh^WU6 mutant larvae are uncoordinated and exhibit a tail-flip phenotype indicative of posterior paralysis and compromised axonal transport. Immunohistological analysis of axons of the peripheral nervous system of ssh^WU6 larvae, however, fails to reveal focal swellings and accumulations of transported components, indicating that axonal transport is not disrupted. Given the role of ssh in the regulation of microfilaments, we examined the morphology of glutamatergic neuromuscular synapses in ssh^WU6 larvae. Type Is and Ib synapses at ventral longitudinal muscles 6/7 from segments A2 through A5 were quantified on two metrics: ssh^WU6 mutant synapses were morphologically larger than wildtype in both average area (m²) (p<0.01) and average number of boutons (p<0.0001). These results suggest a requirement for the cofilin binding region of ssh in normal phosphatase function and the maintenance of synapse morphology.