Sorbonne Universités, CNRS, Laboratoire de Biologie du Développement de Villefranche-sur-mer (LBDV), 06234 Villefranche-sur-mer, France.
Cells. 2020 Apr 28;9(5):1087. doi: 10.3390/cells9051087.
In eukaryotic cells, a spindle assembly checkpoint (SAC) ensures accurate chromosome segregation, by monitoring proper attachment of chromosomes to spindle microtubules and delaying mitotic progression if connections are erroneous or absent. The SAC is thought to be relaxed during early embryonic development. Here, we evaluate the checkpoint response to lack of kinetochore-spindle microtubule interactions in early embryos of diverse animal species. Our analysis shows that there are two classes of embryos, either proficient or deficient for SAC activation during cleavage. Sea urchins, mussels, and jellyfish embryos show a prolonged delay in mitotic progression in the absence of spindle microtubules from the first cleavage division, while ascidian and amphioxus embryos, like those of and zebrafish, continue mitotic cycling without delay. SAC competence during early development shows no correlation with cell size, chromosome number, or kinetochore to cell volume ratio. We show that SAC proteins Mad1, Mad2, and Mps1 lack the ability to recognize unattached kinetochores in ascidian embryos, indicating that SAC signaling is not diluted but rather actively silenced during early chordate development.
在真核细胞中，纺锤体组装检查点（SAC）通过监测染色体与纺锤体微管的正确连接，如果连接错误或缺失，则延迟有丝分裂进程，从而确保染色体的准确分离。SAC 被认为在胚胎早期发育过程中是放松的。在这里，我们评估了各种动物物种早期胚胎中缺乏动粒-纺锤体微管相互作用时的检查点反应。我们的分析表明，存在两类胚胎，在第一次卵裂时缺乏纺锤体微管，一类是 SAC 激活功能正常，另一类则是激活功能缺失。海胆、贻贝和水母胚胎在缺乏纺锤体微管的情况下，有丝分裂进程会延长，而文昌鱼和鱼胚胎，与 和斑马鱼一样，没有延迟继续有丝分裂循环。早期胚胎发育过程中的 SAC 功能与细胞大小、染色体数量或动粒与细胞体积比无关。我们表明，SAC 蛋白 Mad1、Mad2 和 Mps1 缺乏识别无附着动粒的能力，这表明 SAC 信号不是被稀释，而是在早期脊索动物发育过程中被主动沉默。
