Expression of neurogenin3 reveals an islet cell precursor population in the pancreas

Abstract

Differentiation of early gut endoderm cells into the endocrine cells forming the pancreatic islets of Langerhans depends on a cascade of gene activation events controlled by transcription factors including the basic helix-loop-helix (bHLH) proteins. To delineate this cascade, we began by establishing the position of neurogenin3, a bHLH factor found in the pancreas during fetal development. We detect neurogenin3 immunoreactivity transiently in scattered ductal cells in the fetal mouse pancreas, peaking at embryonic day 15.5. Although not detected in cells expressing islet hormones or the islet transcription factors Isl1, Brn4, Pax6 or PDX1, neurogenin3 is detected along with early islet differentiation factors Nkx6.1 and Nkx2.2, establishing that it is expressed in immature cells in the islet lineage. Analysis of transcription factor-deficient mice demonstrates that neurogenin3 expression is not dependent on neuroD1/BETA2, Mash1, Nkx2.2, Nkx6.1, or Pax6. Furthermore, early expression of neurogenin3 under control of the Pdx1 promoter is alone sufficient to drive early and ectopic differentiation of islet cells, a capability shared by the pancreatic bHLH factor, neuroD1/BETA2, but not by the muscle bHLH factor, MyoD. However, the islet cells produced in these transgenic experiments are overwhelmingly (alpha) cells, suggesting that factors other than the bHLH factors are required to deviate from a default * cell fate. These data support a model in which neurogenin3 acts upstream of other islet differentiation factors, initiating the differentiation of endocrine cells, but switching off prior to final differentiation. The ability to uniquely identify islet cell precursors by neurogenin3 expression allows us to determine the position of other islet transcription factors in the differentiation cascade and to propose a map for the islet cell differentiation pathway.

Necrostatin-1 Supplementation to Islet Tissue Culture Enhances the In-Vitro Development and Graft Function of Young Porcine Islets

“…Another possible reason for this increase in endocrine cellular content is that the generation of new pancreatic endocrine cells involves both progenitor cell differentiation and endocrine cell proliferation [26,27]. As the transcription factor Ngn3 has been reported to be suppressed after pancreatic progenitor cells differentiate into mature endocrine cells, the decrease in the level of Ngn3-positive pancreatic progenitor cells with culture time in our study is consistent with the increase in the proportion of major endocrine cells [28,29]. This finding is also supported by a previous study, showing a downregulation of Ngn3 expression in human embryonic stem cells (hESCs) as the expression of insulin, glucagon, and somatostatin increases after 24 days of differentiation culture [30].…”

Emerging Treatment Strategies for Diabetes Mellitus and Associated Complications: An Update

“…Neurogenin (Ngn3) is another gene necessary for endocrine pancreas formation. The pdx-1 promoter controls the forced expression of Ngn3, which is sufficient to encourage the production of all endocrine cells [180]. The hepatic cell transfection by adenovirus with Ngn3 prompts insulin formation and the trans-separation of the oval cell population [180].…”

“…The pdx-1 promoter controls the forced expression of Ngn3, which is sufficient to encourage the production of all endocrine cells [180]. The hepatic cell transfection by adenovirus with Ngn3 prompts insulin formation and the trans-separation of the oval cell population [180]. The introduction of neuroD1 into the liver of STZ-induced diabetic mice leads to an increased response to a stimulus upstream and downstream of the pancreatic translating agents, involving Pax6, Nkx6.1, Ngn3, Nkx2.2, and Pax4 without significant hepatotoxicity [181,182].…”

Alpha-to-beta cell trans-differentiation for treatment of diabetes

“…In the developing mouse pancreas, all endocrine cells develop from neurogenin-3 (ngn3) positive endocrine progenitor cells [18,25]. Ngn3 [a class A Basic Helix-Loop-Helix Protein (bHLH)] is expressed in duct-like epithelial cells that are centrally located within the developing mouse pancreas; as these cells differentiate, they down-regulate ngn3 and aggregate into proto-islet structures [26]. Loss of function mutation of ngn3 prevents endocrine development and leads to death in mice postnatally [25,[27][28][29].…”