Revealing how cytoskeletal dynamics form the early mammalian embryo

总结 揭示哺乳动物发育过程中指定第一个分化细胞谱系的关键事件是关键 了解早期胚胎是如何组织植入子宫并怀孕的。第一 哺乳动物细胞谱系包括将形成胎儿的多能内细胞团（ICM）和将形成胎儿的外细胞团（ICM）。 形成胎盘的滋养外胚层。然而，解释这些谱系如何分化的机制是 不清楚在许多非哺乳动物胚胎中，不对称遗传的细胞命运决定因素指定谱系命运， 然而，在哺乳动物的早期发育过程中，类似的机制被认为是不存在的。 我们已经建立了活体成像方法来研究小鼠早期发育过程中的细胞和分子动力学， 发展最近，我们发现了一个新的作用，中间丝组装角蛋白在谱系 规范.我们的研究表明，角蛋白丝是不对称的遗传正是在细胞 物理上分隔未来ICM和滋养外胚层的部分。此外，这些遗产 外部子细胞的纤维有助于确定它们的滋养外胚层身份并促进它们的成熟。 因此，我们的主要假设是角蛋白丝作为一种新形式的不对称遗传因子发挥作用 指定发育过程中的第一滋养外胚层细胞。为了验证这一点，我们将揭示 角蛋白成为不对称遗传（目标1），并可以偏向细胞命运（目标2）。 我们将首先测试如何与蛋白质的相互作用，目前在顶端细胞皮层，和动态的细丝 在细胞内，在细胞分裂过程中控制它们由外部细胞进行的不对称遗传。然后我们将决定如何 角蛋白可以调节细胞力学和极性的关键方面以控制关键转录的分布 决定滋养外胚层命运的因素。 总之，在本提案中，我们将解决一个关于第一个 在哺乳动物发育过程中分化的细胞谱系，并揭示了角蛋白的一些最初的功能 在早期哺乳动物发育过程中的中间丝，与其他细胞骨架元件不同， 像微管和肌动蛋白，仍然是未知的。

SUMMARY Revealing the key events that specify the first differentiated cell lineages during mammalian development is key to understand how the early embryo is organized to implant in the uterus and establish a pregnancy. The first mammalian cell lineages comprise the pluripotent inner cell mass (ICM) that will form the fetus, and the outer trophectoderm that will form the placenta. Yet, the mechanisms explaining how these lineages differentiate are unclear. In many non-mammalian embryos, asymmetrically inherited cell-fate determinants specify lineage fate, yet similar mechanisms are thought to be absent during early mammalian development. We have established live-imaging approaches to study cell and molecular dynamics during early mouse development. Recently, we identified a new role for intermediate filaments assembled by keratins in lineage specification. Our studies reveal that keratin filaments are asymmetrically inherited precisely during the cell divisions that physically segregate the future ICM and trophectoderm. Moreover, the inheritance of these filaments by the outer daughter cells helps to specify their trophectoderm identity and promote their maturation. Thus, our main hypothesis is that keratin filaments function as a new form of asymmetrically inherited factor specifying the first trophectoderm cells during development. To test this, we will reveal the mechanisms by which keratins become asymmetrically inherited (Aim 1) and can bias cell fate (Aim 2). We will first test how interactions with proteins present at the apical cell cortex, and the dynamics of the filaments inside the cell, control their asymmetric inheritance by outer cells during cell division. We will then determine how keratins can regulate key aspects of cell mechanics and polarity to control the distribution of the key transcription factors that specify trophectoderm fate. In summary, in this proposal we will address a fundamental open question about the specification of the first differentiated cell lineages during mammalian development, and unveil some of the first functions of keratin intermediated filaments during early mammalian development, which unlike those of other cytoskeletal elements like microtubules and actin, remain largely unknown.