In single celled eukaryotes, the pathways that monitor nutrient availability are central to regulating the meiotic program and spore development. However, how metabolic inputs influence meiotic progression and gametogenesis remains poorly understood in metazoans. Our current studies focus on understanding how metabolism influences meiotic progression and oocyte development. Target of rapamycin complex 1 (TORC1) is a master regulator of metabolism in eukaryotes that integrates information from multiple upstream signaling pathways. The GATOR1 complex inhibits TORC1 in response to amino acid limitation and is required for meiotic entry in yeast. To define the role of the GATOR1 complex in Drosophila, we generated null alleles of all three GATOR1 components, nprl2, nprl3 and iml1 using CRISPR/CAS9. Analysis of these mutants revealed that, as is observed in yeast, the GATOR1 complex down-regulates TORC1 activity to promote the transition from the mitotic to the meiotic cycle. Moreover, the delayed entry into meiosis can be suppressed by feeding the females the TORC1 inhibitor Rapamycin. Finally, we determined that mutations in Tor kinase, result in premature meiotic entry. Thus in Drosophila females, high TORC1 activity inhibits the mitotic/meiotic transition and gamete development while low TORC1 activity promotes these events. Currently, we are using genetic strategies to determine what downstream targets of TORC1 mediate the meiotic delay. To complement this line of investigation, we are examining if the GATOR1 complex has critical functions in the early stages of meiosis. Intriguingly, we determined that in nprl2, nprl3 and iml1 mutants the formation of meiotic double-stranded breaks is deregulated resulting in a dramatic increase in the number of meiotic double-stranded breaks and in the activation of the transcription factor p53. In mammals, all three members of the GATOR1 complex function as tumor suppressor genes. However, the precise role of the GATOR1 complex in the regulation of metabolism in metazoans remained poorly defined. We have shown that that the central importance of Nprl2, Nprl3 and Iml1 in the response to amino acid starvation has been conserved from single cell to multicellular animals. We find that in Drosophila, Nprl2, Nprl3 and Iml1 physically interact and are targeted to lysosomes and autolysosomes. Using oogenesis as a model system, we demonstrated that the GATOR1 complex inhibits TORC1 signaling in response to amino acid starvation. Moreover, the inhibition TORC1 by the GATOR1 complex is critical to the preservation of female fertility during times of protein scarcity. In young egg chambers the failure to down-regulate TORC1 in response to amino acid limitation triggers apoptosis. Thus, our data suggest the presence of a metabolic checkpoint that initiates a cell death program when TORC1 activity remains inappropriately high during periods of amino acid and/or nutrient scarcity in oogenesis. Going forward, we will continue to use Drosophila as a model system to study how the GATOR complex helps integrate developmental and metabolic inputs.
Showing the most recent 10 out of 11 publications
