卵细胞减数分裂的新机制

　　

    生物通报道  美国加利福尼亚大学、圣地亚哥医学院和Ludwig癌症研究所的研究者发现了有性生殖生物细胞减数分裂生成生殖细胞的一种新的特殊机制。研究者通过这个特殊机制解释了卵细胞染色体分离时发生染色体分配错误导致唐氏综合征的原因。这一发现在《Nature Cell Biology.》上发表。

    有性生殖就是精子和卵子在受精时发生染色体合并的过程。精子和卵子是经过减数分裂形成的，减数分裂时细胞连续分裂两次，基因组复制一次从而导致染色体数目减少。精子和卵子拥有一半的亲代染色体，通过精子和卵子的结合使细胞的染色体重新获得两个拷贝。

    减数分裂和有丝分裂都需要特异性蛋白聚合体即微管的参与。微管聚合形成一个似纺锤的结构称为纺锤体，纺锤体的末端微管与特异性细胞器中心粒相连。卵细胞缺乏中心粒，它利用微管自组装成纺锤体。人类卵细胞在减数分裂时可发染色体分离错误。这些错误可以导致人类发生生殖相关的问题例如唐氏综合征、不孕和流产。

    利福尼亚大学圣地亚哥医学院细胞与分子医学系教授、Ludwig癌症研究所研究员Arshad Desai博士利用秀丽隐杆线虫作为研究细胞分裂的模型。Desai实验室的一位博士后人员Julien Dumont利用延时成像显微技术高精度观察了卵细胞的减数分裂。

    在此研究前，细胞染色体分离被认为是通过拉动微管聚合体移动到纺锤体的末端。UCSD的研究人员发现在线虫卵细胞中染色体是被推到中间分离的，在分离染色体间生成了微管聚合物。

    “这一发现表明卵细胞使用了一种特异的机制进行减数分裂染色体分离。”Desai说：“因为卵细胞减数分裂缺陷可导致人类不孕，因而这个机制是非常重要的发现。”

（生物通：何嫱）

生物通原文出处推荐
Nature Cell Biology (2010) doi:10.1038/ncb2093

A kinetochore-independent mechanism drives anaphase chromosome separation during acentrosomal meiosis

Julien Dumont,Karen Oegema& Arshad Desai
Although assembly of acentrosomal meiotic spindles has been extensively studied1, little is known about the segregation of chromosomes on these spindles. Here, we show in Caenorhabditis elegans oocytes that the kinetochore protein, KNL-1, directs assembly of meiotic kinetochores that orient chromosomes. However, in contrast to mitosis, chromosome separation during meiotic anaphase is kinetochore-independent. Before anaphase, meiotic kinetochores and spindle poles disassemble along with the microtubules on the poleward side of chromosomes. During anaphase, microtubules then form between the separating chromosomes. Functional analysis implicated a set of proteins that localize to a ring-shaped domain between kinetochores during pre-anaphase spindle assembly and anaphase separation. These proteins are localized by the chromosomal passenger complex, which regulates the loss of meiotic chromosome cohesion2, 3, 4. Thus, meiotic segregation in C. elegans is a two-stage process, where kinetochores orient chromosomes, but are then dispensable for their separation. We suggest that separation is controlled by a meiosis-specific chromosomal domain to coordinate cohesin removal and chromosome segregation.