H3K4 trimethylation is required for postnatal pancreatic endocrine cell functional maturation

During pancreas development, endocrine progenitors differentiate into the islet-cell subtypes, which undergo further functional maturation in postnatal islet development. In islet b-cells, genes involved in glucose-stimulated insulin secretion are activated and glucose exposure increases the insulin response as b-cells mature. Here, we investigated the role of H3K4 trimethylation in endocrine cell differentiation and functional maturation by disrupting TrxG complex histone methyltransferase activity in mouse endocrine progenitors. In the embryo, genetic inactivation of TrxG component Dpy30 in NEUROG3+ cells did not affect the number of endocrine progenitors or endocrine cell differentiation. H3K4 trimethylation was progressively lost in postnatal islets and the mice displayed elevated non-fasting and fasting glycemia, as well as impaired glucose tolerance by postnatal day 24. Although postnatal endocrine cell proportions were equivalent to controls, islet RNA-sequencing revealed a downregulation of genes involved in glucose-stimulated insulin secretion and an upregulation of immature b-cell genes. Comparison of histone modification enrichment profiles in NEUROG3+ endocrine progenitors and mature islets suggested that genes downregulated by loss of H3K4 trimethylation more frequently acquire active histone modifications during maturation. Taken together, these findings suggest that H3K4 trimethylation is required for the activation of genes involved in the functional maturation of pancreatic islet endocrine cells. Overall design: RNA-sequencing of postnatal day 24 control and Dpy30 knockout islets, including 3 biological replicates

在胰腺发育过程中，内分泌祖细胞分化为胰岛细胞亚型，这些亚型在出生后胰岛发育阶段进一步完成功能成熟。在胰岛β细胞中，参与葡萄糖刺激胰岛素分泌的基因会被激活，且随着β细胞成熟，葡萄糖暴露会增强其胰岛素应答反应。本研究通过敲除小鼠内分泌祖细胞中的TrxG复合物（TrxG complex）组蛋白甲基转移酶（histone methyltransferase）活性，探究了H3K4三甲基化（H3K4 trimethylation）在内分泌细胞分化与功能成熟过程中的作用。在胚胎阶段，在NEUROG3阳性（NEUROG3+）细胞中敲除TrxG复合物组分Dpy30，并不会影响内分泌祖细胞的数量或内分泌细胞的分化过程。出生后胰岛中的H3K4三甲基化水平逐渐降低，而在出生后第24天时，突变小鼠表现出非空腹血糖与空腹血糖均升高，同时糖耐量受损。尽管出生后内分泌细胞的比例与对照组小鼠无显著差异，但胰岛RNA测序（RNA-sequencing）结果显示，参与葡萄糖刺激胰岛素分泌的基因表达下调，而未成熟β细胞相关基因的表达则出现上调。对NEUROG3阳性内分泌祖细胞与成熟胰岛中的组蛋白修饰富集谱进行比较后发现，因H3K4三甲基化缺失而下调的基因，在成熟过程中更易获得活跃性组蛋白修饰。综上，本研究结果表明，H3K4三甲基化对于激活胰腺胰岛内分泌细胞功能成熟相关的基因是必需的。实验整体设计：对出生后第24天的对照组与Dpy30敲除组小鼠的胰岛进行RNA测序，每组设置3次生物学重复。