Department of Genetics and Development, Russ Berrie Medical Pavilion, Columbia University, New York, New York, USA.
PLoS Genet. 2013;9(2):e1003278. doi: 10.1371/journal.pgen.1003278. Epub 2013 Feb 7.
During pancreatic development, transcription factor cascades gradually commit precursor populations to the different endocrine cell fate pathways. Although mutational analyses have defined the functions of many individual pancreatic transcription factors, the integrative transcription factor networks required to regulate lineage specification, as well as their sites of action, are poorly understood. In this study, we investigated where and how the transcription factors Nkx2.2 and Neurod1 genetically interact to differentially regulate endocrine cell specification. In an Nkx2.2 null background, we conditionally deleted Neurod1 in the Pdx1+ pancreatic progenitor cells, the Neurog3+ endocrine progenitor cells, or the glucagon+ alpha cells. These studies determined that, in the absence of Nkx2.2 activity, removal of Neurod1 from the Pdx1+ or Neurog3+ progenitor populations is sufficient to reestablish the specification of the PP and epsilon cell lineages. Alternatively, in the absence of Nkx2.2, removal of Neurod1 from the Pdx1+ pancreatic progenitor population, but not the Neurog3+ endocrine progenitor cells, restores alpha cell specification. Subsequent in vitro reporter assays demonstrated that Nkx2.2 represses Neurod1 in alpha cells. Based on these findings, we conclude that, although Nkx2.2 and Neurod1 are both necessary to promote beta cell differentiation, Nkx2.2 must repress Neurod1 in a Pdx1+ pancreatic progenitor population to appropriately commit a subset of Neurog3+ endocrine progenitor cells to the alpha cell lineage. These results are consistent with the proposed idea that Neurog3+ endocrine progenitor cells represent a heterogeneous population of unipotent cells, each restricted to a particular endocrine lineage.
在胰腺发育过程中，转录因子级联反应逐渐使前体细胞沿着不同的内分泌细胞命运途径发育。尽管突变分析已经确定了许多胰腺转录因子的功能，但调节谱系特化所需的整合转录因子网络及其作用部位仍知之甚少。在这项研究中，我们研究了转录因子 Nkx2.2 和 Neurod1 如何相互作用以调控内分泌细胞特化。在 Nkx2.2 缺失的背景下，我们在 Pdx1+胰腺祖细胞、Neurog3+内分泌祖细胞或胰高血糖素+α细胞中条件性删除 Neurod1。这些研究确定，在缺乏 Nkx2.2 活性的情况下，从 Pdx1+或 Neurog3+祖细胞群体中去除 Neurod1足以重新建立 PP 和 ε 细胞谱系的特化。相反，在缺乏 Nkx2.2 的情况下，从 Pdx1+胰腺祖细胞群体中去除 Neurod1，但不是从 Neurog3+内分泌祖细胞中去除 Neurod1，足以恢复α细胞的特化。随后的体外报告基因检测表明，Nkx2.2 在α细胞中抑制 Neurod1。基于这些发现，我们得出结论，尽管 Nkx2.2 和 Neurod1 都是促进β细胞分化所必需的，但 Nkx2.2 必须在 Pdx1+胰腺祖细胞群体中抑制 Neurod1，以适当将一部分 Neurog3+内分泌祖细胞特化为α细胞谱系。这些结果与提出的观点一致，即 Neurog3+内分泌祖细胞代表具有单一潜能的异质性细胞群体，每个细胞都局限于特定的内分泌谱系。
