The nuclear pore complex (NPC) mediates the transport of macromolecules between the nucleus and cytoplasm. Recent evidence indicates that structural nucleoporins, the building blocks of the NPC, have a variety of unanticipated cellular functions. Here, we report an unexpected tissue-specific requirement for the structural nucleoporin Seh1 during Drosophila oogenesis. Seh1 is a component of the Nup107-160 complex, the major structural subcomplex of the NPC. We demonstrate that Seh1 associates with the product of the missing oocyte (mio) gene. In Drosophila, mio regulates nuclear architecture and meiotic progression in early ovarian cysts. Like mio, seh1 has a crucial germline function during oogenesis. In both mio and seh1 mutant ovaries, a fraction of oocytes fail to maintain the meiotic cycle and develop as pseudo-nurse cells. Moreover, the accumulation of Mio protein is greatly diminished in the seh1 mutant background. Surprisingly, our characterization of a seh1 null allele indicates that, although required in the female germline, seh1 is dispensable for the development of somatic tissues. Our work represents the first examination of seh1 function within the context of a multicellular organism. In summary, our studies demonstrate that Mio is a novel interacting partner of the conserved nucleoporin Seh1 and add to the growing body of evidence that structural nucleoporins can have novel tissue-specific roles.

In single-cell eukaryotes the pathways that monitor nutrient availability are central to initiating the meiotic program and gametogenesis. In Saccharomyces cerevisiae an essential step in the transition to the meiotic cycle is the down-regulation of the nutrient-sensitive target of rapamycin complex 1 (TORC1) by the increased minichromosome loss 1/ GTPase-activating proteins toward Rags 1 (Iml1/GATOR1) complex in response to amino acid starvation. How metabolic inputs influence early meiotic progression and gametogenesis remains poorly understood in metazoans. Here we define opposing functions for the TORC1 regulatory complexes Iml1/GATOR1 and GATOR2 during Drosophila oogenesis. We demonstrate that, as is observed in yeast, the Iml1/GATOR1 complex inhibits TORC1 activity to slow cellular metabolism and drive the mitotic/meiotic transition in developing ovarian cysts. In iml1 germline depletions, ovarian cysts undergo an extra mitotic division before meiotic entry. The TORC1 inhibitor rapamycin can suppress this extra mitotic division. Thus, high TORC1 activity delays the mitotic/meiotic transition. Conversely, mutations in Tor, which encodes the catalytic subunit of the TORC1 complex, result in premature meiotic entry. Later in oogenesis, the GATOR2 components Mio and Seh1 are required to oppose Iml1/GATOR1 activity to prevent the constitutive inhibition of TORC1 and a block to oocyte growth and development. To our knowledge, these studies represent the first examination of the regulatory relationship between the Iml1/GATOR1 and GATOR2 complexes within the context of a multicellular organism. Our data imply that the central role of the Iml1/GATOR1 complex in the regulation of TORC1 activity in the early meiotic cycle has been conserved from single cell to multicellular organisms.