Neurogenin3 inhibits proliferation in endocrine progenitors by inducing Cdkn1a

Diabetes Center, Hormone Research Institute and Department of Medicine, University of California, San Francisco, CA 94143, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 01/2011; 108(1):185-90. DOI: 10.1073/pnas.1004842108
Source: PubMed

ABSTRACT During organogenesis, the final size of mature cell populations depends on their rates of differentiation and expansion. Because transient expression of Neurogenin3 (Neurog3) in progenitor cells in the developing pancreas initiates their differentiation to mature islet cells, we examined the role of Neurog3 in cell cycle control during this process. We found that mitotically active pancreatic progenitor cells in mouse embryos exited the cell cycle after the initiation of Neurog3 expression. Transcriptome analysis demonstrated that the Neurog3-expressing cells dramatically up-regulated the mRNA encoding cyclin-dependent kinase inhibitor 1a (Cdkn1a). In Neurog3 null mice, the islet progenitor cells failed to activate Cdkn1a expression and continued to proliferate, showing that their exit from the cell cycle requires Neurog3. Furthermore, induced transgenic expression of Neurog3 in mouse β-cells in vivo markedly decreased their proliferation, increased Cdkn1a levels, and eventually caused profound hyperglycemia. In contrast, in Cdkn1a null mice, proliferation was incompletely suppressed in the Neurog3-expressing cells. These studies reveal a crucial role for Neurog3 in regulating the cell cycle during the differentiation of islet cells and demonstrate that the subsequent down-regulation of Neurog3 allows the mature islet cell population to expand.

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    • ") (Georgia et al., 2006; Miyatsuka et al., 2011). Multiple transcription factors regulate pancreatic endocrine cell development, and they have interacting and sometimes opposing functions. "
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    ABSTRACT: Insulinoma associated 1 (Insm1) plays an important role in regulating the development of cells in the central and peripheral nervous systems, olfactory epithelium and endocrine pancreas. To better define the role of Insm1 in pancreatic endocrine cell development we generated mice with an Insm1(GFPCre) reporter allele and used them to study Insm1-expressing and null populations. Endocrine progenitor cells lacking Insm1 were less differentiated and exhibited broad defects in hormone production, cell proliferation and cell migration. Embryos lacking Insm1 contained greater amounts of a non-coding Neurog3 mRNA splice variant and had fewer Neurog3/Insm1 co-expressing progenitor cells, suggesting that Insm1 positively regulates Neurog3. Moreover, endocrine progenitor cells that express either high or low levels of Pdx1, and thus may be biased towards the formation of specific cell lineages, exhibited cell type-specific differences in the genes regulated by Insm1. Analysis of the function of Ripply3, an Insm1-regulated gene enriched in the Pdx1-high cell population, revealed that it negatively regulates the proliferation of early endocrine cells. Taken together, these findings indicate that in developing pancreatic endocrine cells Insm1 promotes the transition from a ductal progenitor to a committed endocrine cell by repressing a progenitor cell program and activating genes essential for RNA splicing, cell migration, controlled cellular proliferation, vasculogenesis, extracellular matrix and hormone secretion.
    Development 08/2014; 141(15):2939-49. DOI:10.1242/dev.104810 · 6.46 Impact Factor
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    • "The above results do not support reactivation of the Ngn3 pathway as a mechanism of generating more β-cells in pregnancy. Instead, the drop in the number of Ngn3-expressing cells and the down-regulation of Ngn3 expression in islets during pregnancy is more consistent with the model proposed by Miyatsuka et al, where high levels of Ngn3 expression was found to keep cells in a state of quiescence while down-regulation of Ngn3 expression is required for cell proliferation [26], [27]. This suggests that during pregnancy, down-regulation of Ngn3 in the islets is a prerequisite for β-cell to enter cell cycle and proliferate. "
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    ABSTRACT: β-cell mass in the pancreas increases significantly during pregnancy as an adaptation to maternal insulin resistance. Lineage tracing studies in rodents have presented conflicting evidence on the role of cell duplication in the formation of new β-cells during gestation, while recent human data suggest that new islets are a major contributor to increased β-cell mass in pregnancy. Here, we aim to: 1) determine whether a non-β-cell source contributes to the appearance of new β-cells during pregnancy and 2) investigate whether recapitulation of the embryonic developmental pathway involving high expression of neurogenin 3 (Ngn3) plays a role in the up-regulation of β-cell mass during pregnancy. Using a mouse β-cell lineage-tracing model, which labels insulin-producing β-cells with red fluorescent protein (RFP), we found that the percentage of labeled β-cells dropped from 97% prior to pregnancy to 87% at mid-pregnancy. This suggests contribution of a non-β-cell source to the increase in total β-cell numbers during pregnancy. In addition, we observed a population of hormone-negative, Ngn3-positive cells in islets of both non-pregnant and pregnant mice, and this population dropped from 12% of all islets cells in the non-pregnant mice to 5% by day 8 of pregnancy. Concomitantly, a decrease in expression of Ngn3 and changes in its upstream regulatory network (Sox9 and Hes-1) as well as downstream targets (NeuroD, Nkx2.2, Rfx6 and IA1) were also observed during pregnancy. Our results show that duplication of pre-existing β-cells is not the sole source of new β-cells during pregnancy and that Ngn3 may be involved in this process.
    PLoS ONE 06/2014; 9(6):e100398. DOI:10.1371/journal.pone.0100398 · 3.23 Impact Factor
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    • "Ngn3, transiently expressed in committed precursors, is essential to their endocrine differentiation [3], [28] and involved in islet formation [48] and β-cell regeneration [33], [42]. Obestatin increased Ngn3 gene expression in MLCs at day 9 and reduced their proliferation, suggesting commitment toward the endocrine fate [31]. "
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    ABSTRACT: Availability of large amounts of in vitro generated β-cells may support replacement therapy in diabetes. However, methods to obtain β-cells from stem/progenitor cells are limited by inefficient endocrine differentiation. We have recently shown that the ghrelin gene product obestatin displays beneficial effects on pancreatic β-cell survival and function. Obestatin prevents β-cell apoptosis, preserves β-cell mass and stimulates insulin secretion in vitro and in vivo, in both normal and diabetic conditions. In the present study, we investigated whether obestatin may promote in vitro β-cell generation from mouse pancreatic islet-derived precursor cells. Treatment of cultured islets of Langerhans with obestatin (i) enriched cells expressing the mesenchymal/neuronal marker nestin, which is associated with pancreatic precursors; (ii) increased cell survival and reduced apoptosis during precursor selection; (iii) promoted the generation of islet-like cell clusters (ICCs) with increased insulin gene expression and C-peptide secretion. Furthermore, obestatin modulated the expression of fibroblast growth factor receptors (FGFRs), Notch receptors and neurogenin 3 (Ngn3) during islet-derived precursor cell selection and endocrine differentiation. These results indicate that obestatin improves the generation of functional β-cells/ICCs in vitro, suggesting implications for cell-based replacement therapy in diabetes. Moreover, obestatin may play a role in regulating pathways involved in pancreas development and regeneration.
    PLoS ONE 07/2013; 8(5):e64374. DOI:10.1371/journal.pone.0064374 · 3.23 Impact Factor
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