Whole-genome microRNA screening identifies let-7 and mir-18 as regulators of germ layer formation during early embryogenesis
Whole-genome microRNA screening identifies let-7 and mir-18 as regulators of germ layer formation during early embryogenesis
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DOI：
10.1101/gad.200758.112
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发表时间：
2012-12-01
影响因子：
10.5
通讯作者：
Mercola, Mark
中科院分区：
文献类型：
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作者：
Colas, Alexandre R.;McKeithan, Wesley L.;Mercola, Mark
严格控制内胚层、中胚层和外胚层的分离对于所有物种的正常胚胎发育都是必不可少的，然而相邻的胚胎卵裂球如何有助于不同的胚层从未得到充分解释。我们推测，微调许多生物过程的microRNA可能会调节胚胎卵裂球对生长因子和其他控制胚层命运的信号的反应。对全基因组microRNA文库的系统性筛选显示，let-7和miR-18家族以牺牲小鼠胚胎干细胞中的内胚层为代价增加中胚层。这两个家族都在外胚层和中胚层中表达，但不在内胚层中表达，因为这些组织在小鼠和青蛙胚胎发生期间变得不同。在体内阻断let-7功能显著影响细胞命运，将假定的中胚层和外胚层转移到内胚层。siRNA敲除计算预测的靶点，然后进行突变分析，结果显示let-7和miR-18分别下调Acvr 1b和Smad 2，以减弱Nodal反应性并使卵裂球偏向外胚层和中胚层命运。这些发现表明let-7和miR-18家族在胚层特化中的关键作用，并揭示了从两栖动物到哺乳动物的功能的显着保守。
Tight control over the segregation of endoderm, mesoderm, and ectoderm is essential for normal embryonic development of all species, yet how neighboring embryonic blastomeres can contribute to different germ layers has never been fully explained. We postulated that microRNAs, which fine-tune many biological processes, might modulate the response of embryonic blastomeres to growth factors and other signals that govern germ layer fate. A systematic screen of a whole-genome microRNA library revealed that the let-7 and miR-18 families increase mesoderm at the expense of endoderm in mouse embryonic stem cells. Both families are expressed in ectoderm and mesoderm, but not endoderm, as these tissues become distinct during mouse and frog embryogenesis. Blocking let-7 function in vivo dramatically affected cell fate, diverting presumptive mesoderm and ectoderm into endoderm. siRNA knockdown of computationally predicted targets followed by mutational analyses revealed that let-7 and miR-18 down-regulate Acvr1b and Smad2, respectively, to attenuate Nodal responsiveness and bias blastomeres to ectoderm and mesoderm fates. These findings suggest a crucial role for the let-7 and miR-18 families in germ layer specification and reveal a remarkable conservation of function from amphibians to mammals.