During spermatogenesis, the ER/Golgi derived, fibrous body-membranous organelles (FB-MOs) play a central role in the proper segregation of cytoplasmic components into the spermatids. Normally, FB-MO's arise in the developing spermatocyte. The FB first appears as short fibers of Major Sperm Protein (MSP) in the body of the MO. The FB-MO complexes increase in size as the spermatocyte develops and then segregate to the budding spermatid, transporting material required for these spermatids to undergo spermiogenesis. After the spermatids bud off of the residual body, the FB-MO complex disassociates. MSP fibers depolymerize to reassemble in the pseudopod, and the MO's fuse with the plasma membrane, releasing its contents onto the cell surface and forming a permanent fusion pore. Mutation of
spe-10 prevents the proper function of the FB-MOs and spermatogenesis is disrupted. The FB-MO complexes break down prematurely, the fibrous bodies are left behind in the residual body and do not disassemble as in wild type spermatids. The membranous organelles segregate to spermatids, but then become swollen and vacuolated. Associated with these defects is improper localization of the nucleus in spermatids. So, resulting spermatozoa have vacuolated MO's, short pseudopods, and they fail to translocate. Previous work positioned
spe-10 on chromosome V, covered by deficiency sDf35. Three factor mapping places it between
unc-42 and
sma-1 . (Shakes, D.C., and Ward, S. 1989. Dev. Biol . 134, 307-316.) On the physical map, this region is well represented by overlapping YACs and cosmids. Therefore, we are attempting to clone
spe-10 by transgenic rescue. We have successfully rescued the
spe-10 mutant phenotype by YACs containing wild-type DNA that covers the region between
unc-42 and
sma-1 . We are now attempting cosmid rescue, in order to narrow down this region. Progress towards the cloning of
spe-10 will be reported.