THE DROSOPHILA GENE FS(2)CUP INTERACTS WITH OTU TO DEFINE A CYTOPLASMIC PATHWAY REQUIRED FOR THE STRUCTURE AND FUNCTION OF GERM-LINE CHROMOSOMES

The Drosophila ovarian tumor gene (otu) encodes cytoplasmic proteins t hat are required in germ-line cells for cyst formation, nurse cell chr omosome structure and egg maturation. We have analyzed a gene, fs(2)cu p, that participates in many of the same processes and interacts with otu genetically. Both nurse cell and oocyte chromosomes require cup to attain a normal morphology, In addition, the gene is needed for the o ocyte to grow normally by taking up materials transported from the nur se cells, The gene encodes a 1132-amino-acid protein containing a puta tive membrane-spanning domain. Cup protein (but not cup RNA) is transp orted selectively into the oocyte in germarial cysts, like the p104 Ot u protein, It is strongly associated with large structures in the cyto plasm and perinuclear region of nurse cells and, like Otu, moves to th e periphery of these cells in stages 9-10. Moreover, cup mutations dom inantly disrupt meiotic chromosome segregation, We propose that cup, o tu and another interacting gene,fs(2)B, take part in a common cytoplas mic pathway with multiple functions during oogenesis.