Evolution and the meaning of metaphase.
Evolution and the meaning of metaphase.
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DOI：
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发表时间：
1992-08
影响因子：
4
通讯作者：
R. Nicklas;P. Arana
中科院分区：
文献类型：
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作者：
R. Nicklas;P. Arana
我们使用进化测试来询问染色体向纺锤形赤道聚集本身是重要的，还是仅仅是有丝分裂的偶发事件。如果会议很重要，那么它可能会在最初缺席的情况下演变。以前的工作人员建立了新形成的三价体，减数分裂单位为三条染色体，一般不会开到纺锤体赤道。相反，这些年轻的三价体靠近三条染色体中的两条定向的极点。我们研究了几十万到几百万年前在几种螳螂和一种蝗虫身上出现的古代性染色体三价体。所有这些旧的三价体都在中期的纺锤形赤道附近；其中一些与同一细胞中的普通染色体一样精确地延伸到赤道。我们得出结论，在所研究的材料中，会议独立地演化了两到三次。因此，两极之间染色体的中期位置似乎很重要，但为什么呢？在螳螂身上，明显的答案是中期是一个质量控制检查点。有时，这三条染色体并不是三价体的，而是以二价体加一条不成对的染色体的形式存在的，该染色体位于一极附近。早期的研究人员表明，这种细胞在中期受阻，最终退化；这阻止了性染色体异常组合的精子的形成。我们认为，质量控制系统将很难区分未配对的染色体和新出现的未配对的三价体，这两种染色体都位于纺锤体极点附近。如果是这样的话，混乱的质量控制系统将轻率地阻止后期，导致本应产生正常精子的细胞的损失。因此，我们得出结论，三价体向赤道的聚集可能是随着中期质量控制检查点而演变的。旧的三价体的收缩机制尚不确定，但可能涉及与特定染色体相关的马达的有趣的力敏感调节。我们还研究了两个新制成的四价体在三个运动中心指向一个极点和一个指向另一个极点时的收缩。正如其他人所描述的那样，其中一个四价体不会运动，而另一个四价体比预期的更接近纺锤形的赤道。退化程度的这种变化可能会为自然选择提供材料，从而导致退化的进化。螳螂的三价体是进一步研究退化机制和中期是细胞周期进程的检查点的诱人材料。
We used an evolutionary test to ask whether the congression of chromosomes to the spindle equator is important in itself or just a mitotic happenstance. If congression matters, then it might evolve if absent initially. Previous workers established that newly made trivalents, meiotic units of three chromosomes, generally do not congress to the spindle equator. Instead, these young trivalents lie close to the pole to which two of the three chromosomes are oriented. We studied ancient sex-chromosome trivalents that arose hundreds of thousands to several million years ago in several species of praying mantids and one grasshopper. All these old trivalents lie near the spindle equator at metaphase; some of them congress as precisely to the equator as the ordinary chromosomes in the same cells. We conclude that congression evolved independently two or three times in the materials studied. Therefore, the metaphase position of chromosomes midway between the poles appears to matter, but why? In the praying mantids, the evident answer is that metaphase is a quality-control checkpoint. Sometimes the three chromosomes are not associated in a trivalent but rather are present as a bivalent plus an unpaired chromosome, which lies near one pole. Earlier workers showed that such cells are blocked in metaphase and eventually degenerate; this prevents the formation of sperm with abnormal combinations of sex chromosomes. We suggest that the quality-control system would have trouble distinguishing an unpaired chromosome from an uncongressed, newly arisen trivalent, both of which would lie near a spindle pole. If so, the confused quality-control system would block anaphase imprudently, causing a loss of cells that would have produced normal sperm. Hence, we conclude that the congression of the trivalent to the equator probably evolved along with the metaphase quality-control checkpoint. The mechanism of congression in old trivalents is uncertain, but probably involves an interesting force-sensitive regulation of the motors associated with particular chromosomes. We also examined the congression of two newly made quadrivalents when they orient with three kinetochores to one pole and one to the other. As others have described, one of these quadrivalents does not congress, while the other quadrivalent comes closer than expected to the spindle equator. Such variation in the extent of congression may provide materials on which natural selection can act, leading to the evolution of congression. The trivalents of praying mantids are attractive materials for further studies of the mechanism of congression and of the idea that metaphase is a checkpoint for progression through the cell cycle.