The fragle centrioles (fract) gene is required for the maintenance of centriole integrity during Drosophila male meiosis

We isolated a mutation in a Drosophila gene we name fragile centrioles (fract); this mutation disrupts male meiosis and causes male sterility. Staining for centriolar components such as DSpd2 and Asl showed that premeiotic spermatocytes of fract mutants display 2 normal centrioles at each cell pole. However, the cell poles of meiotic ana-telophases I of fract mutants often exhibit defective centrioles. As a result, 60% of secondary spermatocytes assemble bipolar monastral spindles that are unable to mediate proper chromosome segregation. fract encodes a 322 aa protein expressed only in testes, suggesting that it is specifically required for meiotic centriole stability. The fract1 mutant allele we characterized carries a stop codon that truncates the Fract protein into a 298 aa polypeptide. A polyclonal antibody raised against Fract decorates the distal ends of male meiotic centrioles. A centriole stability assay indicated that the centrioles of fract mutants are more sensitive to colchicine- or cold-induced depolymerization than their wild type counterparts. We also asked which factors are responsible for centriole depolymerization in fract mutants not exposed to colchicine or cold. We constructed flies homozygous for fract1 and heterozygous for mutations in either Dhc64 or Klp61F, which encode the dynein heavy chain and the (Eg5-homologue) Kinesin-like protein at 61F, respectively. In these flies the centrioles were substantially more stable than in fract mutant flies. Thus, lowering MT-dependent pulling and pushing forces on centrosomes by dynein or kinesin partial depletion rescues the centriole phenotype of fract mutants. Collectively, our results indicate that fract is not required for centriole assembly but is essential for stress resistance of centrioles during male meiosis.