Lerner Research Institute, Cleveland Clinic, 9500 Euclid Ave, Cleveland, OH 44195, USA.
Dev Biol. 2013 Apr 1;376(1):1-12. doi: 10.1016/j.ydbio.2013.01.021. Epub 2013 Jan 29.
Ngn3 is recognized as a regulator of pancreatic endocrine formation, and Notch signaling as an important negative regulator Ngn3 gene expression. By conditionally controlling expression of Ngn3 in the pancreas, we find that these two signaling components are dynamically linked. This connection involves transcriptional repression as previously shown, but also incorporates a novel post-translational mechanism. In addition to its ability to promote endocrine fate, we provide evidence of a competing ability of Ngn3 in the patterning of multipotent progenitor cells in turn controlling the formation of ducts. On one hand, Ngn3 cell-intrinsically activates endocrine target genes; on the other, Ngn3 cell-extrinsically promotes lateral signaling via the Dll1>Notch>Hes1 pathway which substantially limits its ability to sustain endocrine formation. Prior to endocrine commitment, the Ngn3-mediated activation of the Notch>Hes1 pathway impacts formation of the trunk domain in the pancreas causing multipotent progenitors to lose acinar, while gaining endocrine and ductal, competence. The subsequent selection of fate from such bipotential progenitors is then governed by lateral inhibition, where Notch>Hes1-mediated Ngn3 protein destabilization serves to limit endocrine differentiation by reducing cellular levels of Ngn3. This system thus allows for rapid dynamic changes between opposing bHLH proteins in cells approaching a terminal differentiation event. Inhibition of Notch signaling leads to Ngn3 protein stabilization in the normal mouse pancreas explants. We conclude that the mutually exclusive expression pattern of Ngn3/Hes1 proteins in the mammalian pancreas is partially controlled through Notch-mediated post-translational regulation and we demonstrate that the formation of insulin-producing beta-cells can be significantly enhanced upon induction of a pro-endocrine drive combined with the inhibition of Notch processing.
Ngn3 被认为是胰腺内分泌形成的调节剂，而 Notch 信号作为 Ngn3 基因表达的重要负调节剂。通过条件性控制胰腺中 Ngn3 的表达，我们发现这两个信号成分是动态关联的。这种联系涉及到先前显示的转录抑制，但也包含了一种新的翻译后机制。除了促进内分泌命运的能力外，我们还提供了证据表明，Ngn3 有能力在多能祖细胞的模式形成中竞争，从而控制导管的形成。一方面，Ngn3 细胞内在地激活内分泌靶基因；另一方面，Ngn3 细胞外在地通过 Dll1> Notch>Hes1 途径促进侧向信号，这大大限制了它维持内分泌形成的能力。在内分泌承诺之前，Ngn3 介导的 Notch>Hes1 途径的激活会影响胰腺主干域的形成，导致多能祖细胞失去腺泡，而获得内分泌和导管的能力。随后，这种双潜能祖细胞的命运选择受到侧向抑制的控制，其中 Notch>Hes1 介导的 Ngn3 蛋白不稳定性通过降低细胞内 Ngn3 水平来限制内分泌分化。因此，该系统允许在接近终末分化事件的细胞中，相反的 bHLH 蛋白之间发生快速动态变化。在正常小鼠胰腺外植体中， Notch 信号的抑制导致 Ngn3 蛋白的稳定。我们得出结论，哺乳动物胰腺中 Ngn3/Hes1 蛋白的互斥表达模式部分受 Notch 介导的翻译后调控控制，我们证明，在诱导前内分泌驱动并抑制 Notch 处理的情况下，胰岛素产生的β细胞的形成可以显著增强。
