Laboratory of Biology and Modeling of the Cell, Ecole Normale Supérieure de Lyon, CNRS, Inserm, UCBL, Lyon, France.
The Francis Crick Institute, London, United Kingdom.
Curr Top Dev Biol. 2021;144:269-308. doi: 10.1016/bs.ctdb.2020.12.006. Epub 2021 Feb 16.
Starting with Boveri in the 1870s, microscopic investigation of early embryogenesis in a broad swath of nematode species revealed the central role of asymmetric cell division in embryonic axis specification, blastomere positioning, and cell fate specification. Notably, across the class Chromadorea, a conserved theme emerges-asymmetry is first established in the zygote and specifies its asymmetric division, giving rise to an anterior somatic daughter cell and a posterior germline daughter cell. Beginning in the 1980s, the emergence of Caenorhabditis elegans as a model organism saw the advent of genetic tools that enabled rapid progress in our understanding of the molecular mechanisms underlying asymmetric division, in many cases defining key paradigms that turn out to regulate asymmetric division in a wide range of systems. Yet, the consequence of this focus on C. elegans came at the expense of exploring the extant diversity of developmental variation exhibited across nematode species. Given the resurgent interest in evolutionary studies facilitated in part by new tools, here we revisit the diversity in this asymmetric first division, juxtaposing molecular insight into mechanisms of symmetry-breaking, spindle positioning and fate specification, with a consideration of plasticity and variability within and between species. In the process, we hope to highlight questions of evolutionary forces and molecular variation that may have shaped the extant diversity of developmental mechanisms observed across Nematoda.
从 19 世纪 70 年代的博韦里开始，对广泛的线虫物种的早期胚胎发生的微观研究揭示了不对称细胞分裂在胚胎轴特化、胚胎细胞定位和细胞命运特化中的核心作用。值得注意的是，在 Chromadorea 类中，出现了一个保守的主题——不对称性首先在合子中建立，并指定其不对称分裂，产生一个前体细胞和一个后体细胞。自 20 世纪 80 年代以来，秀丽隐杆线虫作为一种模式生物的出现，带来了遗传工具的出现，使我们对不对称分裂的分子机制的理解取得了快速进展，在许多情况下，定义了调节广泛系统中不对称分裂的关键范例。然而，这种对秀丽隐杆线虫的关注的结果是以牺牲探索线虫物种中表现出的现存发育变异多样性为代价的。鉴于部分新工具的出现再次引发了对进化研究的兴趣，在这里，我们重新审视了这种不对称的第一次分裂的多样性，将对称性破缺、纺锤体定位和命运特化的机制的分子见解与对种内和种间的可塑性和可变性的考虑并列。在这个过程中，我们希望强调可能塑造了线虫目中观察到的现存发育机制多样性的进化力量和分子变异的问题。
