PAR-1 is required for the maintenance of oocyte fate in Drosophila

The PAR-1 kinase is required for the posterior localisation of the germline determinants in C. elegans and Drosophila, and localises to the posterior of the zygote and the oocyte in each case. We show that Drosophila PAR-1 is also required much earlier in oogenesis for the selection of one cell in a germline cyst to become the oocyte, Although the initial steps in oocyte d etermination are delayed, three markers for oocyte identity, the synaptonem al complex, the centrosomes and Orb protein, still become restricted to one cell in mutant clones. However, the centrosomes and Orb protein fail to tr anslocate from the anterior to the posterior cortex of the presumptive oocy te in region 3 of the germarium, and the cell exits meiosis and becomes a n urse cell. Furthermore, markers for the minus ends of the microtubules also fail to move from the anterior to the posterior of the oocyte in mutant cl ones. Thus, PAR-1 is required for the maintenance of oocyte identity, and p lays a role in microtubule-dependent localisation within the oocyte at two stages of oogenesis, Finally, we show that PAR-1 localises on the fusome, a nd provides a link between the asymmetry of the fusome and the selection of the oocyte.