Keating H H, White J G
Laboratory of Molecular Biology and Department of Anatomy, University of Wisconsin-Madison, Madison, WI 53706, USA.
J Cell Sci. 1998 Oct;111 ( Pt 20):3027-33. doi: 10.1242/jcs.111.20.3027.
The early Caenorhabditis elegans embryo divides with a stereotyped pattern of cleavages to produce cells that vary in developmental potential. Differences in cleavage plane orientation arise between the anterior and posterior cells of the 2-cell embryo as a result of asymmetries in centrosome positioning. Mechanisms that position centrosomes are thought to involve interactions between microtubules and the cortex, however, these mechanisms remain poorly defined. Interestingly, in the early embryo the shape of the centrosome predicts its subsequent movement. We have used rhodamine-tubulin and live imaging techniques to study the development of asymmetries in centrosome morphology and positioning. In contrast to studies using fixed embryos, our images provide a detailed characterization of the dynamics of centrosome flattening. In addition, our observations of centrosome behavior in vivo challenge previous assumptions regarding centrosome separation by illustrating that centrosome flattening and daughter centrosome separation are distinct processes, and by revealing that nascent daughter centrosomes may become separated from the nucleus. Finally, we provide evidence that the midbody specifies a region of the cortex that directs rotational alignment of the centrosome-nucleus complex and that the process is likely to involve multiple interactions between microtubules and the cortex; the process of alignment involves oscillations and overshoots, suggesting a multiplicity of cortical sites that interact with microtubules.
早期秀丽隐杆线虫胚胎以一种固定的卵裂模式进行分裂，产生具有不同发育潜能的细胞。由于中心体定位的不对称性，二细胞胚胎的前后细胞之间出现了卵裂平面方向的差异。人们认为，定位中心体的机制涉及微管与皮层之间的相互作用，然而，这些机制仍未明确界定。有趣的是，在早期胚胎中，中心体的形状预示着其随后的移动。我们使用罗丹明微管蛋白和实时成像技术来研究中心体形态和定位不对称性的发展。与使用固定胚胎的研究不同，我们的图像详细描述了中心体扁平化的动态过程。此外，我们对体内中心体行为的观察对先前关于中心体分离的假设提出了挑战，这体现在：中心体扁平化和子代中心体分离是不同的过程，并且新生的子代中心体可能与细胞核分离。最后，我们提供证据表明，中间体确定了皮层的一个区域，该区域指导中心体 - 细胞核复合体的旋转排列，并且该过程可能涉及微管与皮层之间的多种相互作用；排列过程涉及振荡和超调，这表明存在多个与微管相互作用的皮层位点。
