THE DROSOPHILA KINESIN-LIKE PROTEIN KLP3A IS REQUIRED FOR PROPER BEHAVIOR OF MALE AND FEMALE PRONUCLEI AT FERTILIZATION

Drosophila melanogaster females homozygous for mutations in the gene e ncoding the kinesin-like protein KLP3A are sterile (Williams et al., 1 995). We have investigated the basis of this sterility The eggs produc ed by KLP3A mutant mothers are fertilized by sperm, and female meiosis appears to occur normally However, the large majority of these embryo s arrest their development soon thereafter with a characteristic pheno type. The four nuclei produced by female meiosis associate together in a polar body-like structure, while a bipolar spindle is established a round the metaphase-arrested male pronucleus. Thus, the major defect c aused by depletion of the KLP3A protein is either in specification of the female pronucleus, or in migration of the male and female pronucle i toward each other. We have also found that the KLP3A protein is loca ted throughout the metaphase spindle during meiosis and the early embr yonic mitotic divisions, but later accumulates specifically at the mid zone of these same spindles during telophase, The protein is also pres ent on two other microtubule structures: the sperm aster; and the radi al, monastral array of microtubules established between the two meiosi s II spindles. We discuss these results in light of possible functions of the KLP3A protein in pronuclear specification and migration.