The mechanisms by which cellular quiescence, a reversible state of cell cycle exit, is achieved over long periods of time are not fully elucidated but are highly relevant to human disease, particularly cancer, which involves heavy dysregulation of the cell cycle but also may require quiescence for processes such as metastasis. Two genes known to be important for quiescence in mammalian systems include PTEN (phosphatase and tensin homolog) and the transcription factor FOXO (Forkhead box class O). Both of these genes are conserved in the nematode Caenorhabditis elegans, which provides a tractable model system with a powerful genetic toolbox. C. elegans is in particular an excellent model for studying quiescence since, in adverse environmental conditions, it can enter a stage called dauer arrest in which postembryonic development is interrupted for months and cells in developing tissues must maintain quiescence until conditions improve. One of the organs whose development is halted by dauer diapause is the gonad, which consists of both the somatic gonad and the germline. Both the C. elegans homolog of PTEN, DAF-18, and of FOXO, DAF-16, are required to maintain quiescence in the somatic gonad and germline. In order to elucidate how quiescence is maintained in response to environmental context, this proposal will focus on DAF-18/PTEN and DAF-16/FOXO function in the dauer gonad as a model of quiescence. DAF-18 is known to be required for germline quiescence in dauer, and unpublished studies show both DAF-18 and DAF-16 are required for quiescence in the somatic gonad. This proposal will further characterize the role of DAF-18 in maintaining quiescence in the somatic gonad and the germline in dauer through the following aims: first, to better characterize daf-18 function in regulating somatic gonad and germline quiescence in dauer through use of proliferation markers and to determine its tissue specificity in this function; second, to use genetic analysis to identify the signaling pathways regulated by daf-18 to maintain quiescence in the dauer gonad and to test for daf-18 and daf-16 regulation of a canonical cell cycle regulator as a mechanism of maintaining quiescence; third, to conduct a screen for novel regulators of somatic gonad quiescence in dauer using markers of proliferation. Understanding how DAF-18/PTEN and DAF-16/FOXO regulate quiescence and identifying novel regulators in C. elegans - a genetic model complex enough to recapitulate the numerous signaling pathways involved - will help clarify the mechanism by which quiescence is achieved in complex mammalian contexts. Understanding this mechanism will have relevance for human disease and therapy involving quiescence, including cancer and the means by which it can utilize dormancy to evade therapies and metastasize.
How cells maintain quiescence - a state in which cells do not divide but retain the ability to do so - is relevant to human diseases ranging from cancer to challenges in fertility. This project will investigate the mechanisms by which the genes PTEN and FOXO regulate quiescence in cells. A better understanding of how these genes regulate quiescence will help therapeutically address this process in the context of human disease.