RTC1, a conserved SEA complex component, is required for early oogenesis in Drosophila. Weili Cai, Mary Lilly. NICHD, National Institute of Health, Besthesda, MD.

   Meiosis is a variant cell cycle program for sexual reproduction in eukaryotes. We are interested in how meiosis is regulated in the context of a multicellular organism. Drosophila oogenesis is a powerful model system to study the regulation of meiotic progression and gametogenesis, and has proven especially useful in studying gene functions that are conserved in metazoans. Previously, we identified two genes, missing oocyte(mio) and seh1, required for the maintenance of the meiotic cycle during Drosophila oogenesis. In the absence of mio and seh1, the oocytes fate cannot be maintained. mio and seh1 oocytes enter the endocycle and develop as pseudo-nurse cells. Egg chambers are arrested and rarely develop beyond stage 5 of oogenesis. In yeast, the MIO and SEH1 proteins associate with a newly identified complex (SEA-complex). This complex regulates nutritional sensing and metabolism upstream of the Target of the Rapamycin (TOR) signaling pathway. RTC1 is another conserved component of the SEA-complex in yeast and has been implicated in the regulation of the early meiotic cycle and sporulation. To further study the function of this complex in Drosophila, we identified CG7609 as the homolog of RTC1 in Drosophila. We found that CG7609 physically and genetically associates with MIO and SEH1. CG7609 has an exclusively high transcription level in ovaries, indicating a potential important function in ovaries. We also identified a P-element insertion line as a potential null allele. RT-PCR experiments showed that homozygous flies of this P-element insertion line do not produce CG7609 transcript. CG7609 null mutants are not lethal but females are sterile, suggesting an important oogeneic function. Intriguingly, ovarioles from CG7609 mutants had multiple defects during oogenesis. In summary, our data strongly suggest that Drosophila RTC1, CG7609, is a component of the SEA-complex and plays a critical role in the regulation of meiotic progression and/or gametogenesis.