Analysis of mechanisms common to cytokinesis and polarized cell growth in the Drosophila male germline. R.M. Farkas ¹, M.G. Giansanti ², S. Bonaccorsi ², M. Gatti ², M.T. Fuller ¹. 1) Dept Developmental Biol, Stanford Univ Sch Medicine, Stanford, CA; 2) Dept Genetics, Universita di Roma, "La Sapienza," Rome, Italy.

   Discovery of a new class of Drosophila mutants suggests that cytokinesis and polarized cell growth involve similar mechanisms. In males mutant for onr, fun, fws, bns, or fsco (provided by B. Wakimoto, D. Lindsley, and C. Zucker), spermatids contain multiple normal-sized nuclei and large mitochondrial derivatives, reflecting a failure in cytokinesis. Unlike previously characterized Drosophila cytokinesis mutants, these new mutants also have a striking defect in spermatid elongation. Whereas wild type testes contain 2mm-long bundles of parallel spermatids, testes of the new mutants contain spherical spermatid bundles with disorganized axonemes. To identify the mechanisms common to cytokinesis and polarized cell growth, we are analyzing the mutant phenotypes at the subcellular level and cloning the disrupted genes. Late telophase cells mutant for bns accumulate excess F-actin, suggesting that bns is required for actin disassembly. In fws, fun, onr, and fsco cells, the contractile ring and central spindle assemble but do not constrict fully. We have cloned fws: it is homologous to human GTC-90, a protein implicated in vesicle trafficking. We hypothesize that Fws, Fun, Onr, and Fsco facilitate membrane addition at the cleavage furrow of dividing spermatocytes and at the leading edge of elongating spermatids.