Differentiation of Embryonic Stem Cells Conditionally Expressing Neurogenin 3

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Abstract
Expression of the proendocrine gene neurogenin 3 (Ngn3) is required for the development of pancreatic islets. To better characterize the molecular events regulated by Ngn3 during development, we have determined the expression profiles of murine embryonic stem cells (mESCs) uniformly induced to overexpress Ngn3. An mESC line was created in order to induce Ngn3 by adding doxycycline to the culture medium. Genome-wide microarray analysis was performed to identify genes regulated by Ngn3 in a variety of contexts, including undifferentiated ESCs and differentiating embryoid bodies (EBs). Genes regulated by Ngn3 in a context-independent manner were identified and analyzed using systematic gene ontology tools. This analysis revealed Notch signaling as the most significantly regulated signaling pathway (p = .009). This result is consistent with the hypothesis that Ngn3 expression makes the cell competent for Notch signaling to be activated and, conversely, more sensitive to Notch signaling inhibition. Indeed, EBs induced to express Ngn3 were significantly more sensitive to gamma-secretase inhibitor-mediated Notch signaling inhibition (p < .0001) when compared with uninduced EBs. Moreover, we find that Ngn3 induction in differentiating ESCs results in significant increases in insulin, glucagon, and somatostatin expression.