Characterization of new Drosophila mutants defective in mitochondrial morphogenesis during spermatogenesis. M.M. Wilson , K.G. Hales. Department of Biology, Davidson College, Davidson, NC.

   During Drosophila spermatogenesis, mitochondria undergo a series of dramatic movements and shape changes, including aggregation, fusion and elongation. We have characterized several new male sterile lines that show defects in mitochondrial morphogenesis during spermatogenesis. These stocks are from a large collection of second- and third-chromosome EMS-mutagenized, homozygous viable lines (E. Koundakjian, R. Hardy, D. Cowen and C. Zuker, personal communication). In two allelic lines, mitochondria aggregate not beside the post-meiotic spermatid nucleus (as in wild type) but instead in a "shell" completely encompassing the nucleus. Five lines appear to have mitochondrial fusion defects; of these, only one is allelic to fzo, the only gene previously shown to affect this process. Five other lines have seemingly normal mitochondrial dynamics through early post-meiotic stages, with defects appearing during elongation and unfurling of mitochondria. Of all the newly-characterized lines, a subset show additional phenotypes such as occasional failure of meiotic cytokinesis or improper nuclear shaping. Recombination mapping of the mutations in these strains will show whether a single mutation causes pleiotropic effects or whether multiple mutations were present on the original chromosome. We will choose those mutant strains with the most specific and striking phenotypes for gene cloning experiments.