TORC1 regulators Iml1/GATOR1 and GATOR2 control meiotic entry and oocyte development in Drosophila

Abstract

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.

Molecular cytogenetic characterization of two Turner syndrome patients with mosaic ring X chromosome

“…As case 1 had a smaller r (X) chromosome compared to case 2, we analysed the additional genes deleted and found that the extra region deleted in case 1 (Xq21.33-Xq22.1) were harbouring genes involved in thyroid hormone signalling, insulin receptor signalling, meiosis regulation, cell cycle regulation and chromatin organization. Alterations in these pathways are reported to be responsible for ovarian dysfunction [1,5,9,31,36,46].…”

The GATOR1 Complex Regulates Metabolic Homeostasis and the Response to Nutrient Stress inDrosophila melanogaster

“…HS-FLP , UAS-RFP FRT19A/nprl2 1 FRT19A , HS-FLP ; Ubi-GFP FRT80B/nprl3 1 FRT80B and HS-FLP ; Ubi-GFP FRT80B/iml1 1 FRT80B flies were used to generate mutant clones in the germline and somatic cells of the ovary as previously reported (Wei et al 2014). Briefly, female flies were heat-shocked for 2 hr at 37° each day for 3 d. Subsequently, flies were cultured in standard media for an additional 2 d before dissection.…”

“…Western blots were performed as described previously (Wei et al 2014). Antibodies were used at the following concentrations: rabbit anti-P-S6K at 1:500 (Cell Signaling) and guinea pig anti-S6K at 1:10,000 (Hahn et al 2010).…”

“…Notably, recent reports have shown that GATOR1 knockouts of iml1/Depdc5 (rat), nprl2 (mouse), and nprl3 (mouse) result in late embryonic lethality, with embryos exhibiting developmental defects in the heart, liver, and brain (Kowalczyk et al 2012; Dutchak et al 2015; Marsan et al 2016). Additionally, in Drosophila , the GATOR1 complex regulates entry into the meiotic cycle during oogenesis (Wei et al 2014). Taken together, these data strongly suggest that, in metazoans, the GATOR1 complex has evolved roles beyond regulating an adaptive response to amino acid starvation.…”

A visual screen for diet-regulated proteins in the Drosophila ovary using GFP protein trap lines

“…In addition, insulin signaling cell autonomously controls the growth of germline cysts and vitellogenesis (Hsu et al, 2008; LaFever and Drummond-Barbosa, 2005), and act through follicle cells to modulate the microtubule cytoskeleton and processing body formation in underlying germline cysts (Burn et al, 2015). The nutrient sensor Target of rapamycin (TOR) has multiple roles in the GSC and follicle stem cell lineages (LaFever et al, 2010; Sun et al, 2010), and its appropriate downregulation on a poor diet is important for survival of previtellogenic egg chambers (Wei et al, 2014). Ecdysone stimulates GSC responsiveness to niche signals, controls germline differentiation, and stimulates oocyte lipid accumulation (Ables et al, 2015; Ables and Drummond-Barbosa, 2010; Konig et al, 2011; Morris and Spradling, 2012; Sieber and Spradling, 2015).…”