Maintenance of beta cell health has significant implications for Diabetes, both Type 1 and Type 2. Intrinsic changes within the beta cell have an impact on the initiation and progression of these debilitating diseases that require life-long management by the patient. Decades of research has identified the concert of events that must occur to generate a beta cell from embryonic progenitors, primarily using rodent models, and deletion of several of these regulators ablates endocrine, and specifically beta cell, populations. Here, we use a combination of sophisticated transgenic mouse models and human stem cell-derived beta cells to identify critical signals that maintain function in insulin producing cells. The overarching goal of this proposal is to elucidate novel functions of the transcription factor Sox9, currently believed to be only active in pancreas progenitors and adult exocrine duct and centroacinar cells. Similar to another transcription factor, Ngn3, our data indicate that Sox9 is expressed at low levels in mature beta cells where it performs critical functions. The consequences of Sox9 loss are less severe that those observed upon elimination of factors known to result in maturity onset of diabetes in the young (MODY), thus reflecting the reality of human Type 2 Diabetes, in which numerous defects culminate in the development of beta cell dysfunction. We pose that Sox9 plays a central role in regulating essential aspects of beta cell development and function. In the first specific aim, we propose to determine the consequences of Sox9 elimination in mature rodent and human beta cells. Our preliminary data demonstrate that low-level expression of Sox9 supports beta cell properties and loss of the transcription factor promotes beta cell dysfunction. In the second specific aim, we will investigate the consequences of forced Sox9 expression in beta cells with the goal of defining the regulatory network controlled by the transcription factor. We anticipate that mining data from transgenic mice with supra-physiological levels of Sox9 in the beta cells will allow us to assign novel roles to proteins previously not known to influence beta cell function. In the third specific aim, we focus on the mechanisms by which Sox9 modulates beta cell function. Our preliminary data indicate that Sox9 regulates formation and thus function of primary cilia, a cellular organelle known to regulate beta cell activities. In summary, we anticipate that the experiments outlined in this proposal will provide a deeper understanding of regulatory networks that are in place to maintain the appropriate and precise functioning of a beta cell. Uncovering the reasons behind beta cell failure should provide novel insights that can be exploited to devise novel therapeutic strategies for the treatment of patients with Diabetes.