Sakaida Tomoyuki, Inomata Shiho, Shinagawa Atsunori
Department of Biology, Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-Machi, Yamagata 990-8560, Japan.
Dev Growth Differ. 2004 Aug;46(4):371-81. doi: 10.1111/j.1440-169x.2004.00754.x.
Kuroda et al. (2001) of our laboratory have previously revealed that exposure of early Xenopus embryos to 150 mm urethane results in complete suppression of formation of the asters and the cleavage furrow, as well as significant reduction of the size of the spindle in the blastomeres, allowing only 1 or 2 cycles of mitosis but not cytokinesis. In the course of closer examination of the effect of urethane on the cleavage of blastomeres of early Xenopus embryos, we unexpectedly discovered that exposure of early Xenopus embryos to 75 mm urethane did not prevent cell division at all, though asters were not detected in the blastomeres. Instead, they contained a spindle that appeared rather normal. They also formed the diastema, a thin yolk-free structure, which is considered to play an essential role in the induction of the cleavage furrow. Essentially the same results were obtained in the exposure of embryos to vinblastine, a well-known microtubule inhibitor: exposure of embryos to 20 micro g/mL vinblastine resulted in complete suppression of cleavage of the blastomeres, where formation of both the spindle and asters were perfectly suppressed. By contrast, exposure of embryos to 5 microg/mL vinblastine did not prevent cleavage in the blastomeres though asters were not detected, whereas the rather normal spindle was formed. Thus, there was a close correlation between the formation of the normal spindle, not asters, and that of the cell division furrow and the diastema in the blastomeres of early Xenopus embryos. We suggest that while the spindle plays an essential role, asters are likely to play only a dispensable role in the induction of the cleavage furrow in even very large cells like the blastomeres of early Xenopus embryos.
我们实验室的黑田等人（2001年）此前曾揭示，将非洲爪蟾早期胚胎暴露于150 mM氨基甲酸乙酯会导致星体和分裂沟的形成完全受到抑制，同时卵裂球中纺锤体的大小显著减小，仅允许进行1或2次有丝分裂周期，但不进行胞质分裂。在更仔细地研究氨基甲酸乙酯对非洲爪蟾早期胚胎卵裂球分裂的影响过程中，我们意外地发现，将非洲爪蟾早期胚胎暴露于75 mM氨基甲酸乙酯根本不会阻止细胞分裂，尽管在卵裂球中未检测到星体。相反，它们含有一个看起来相当正常的纺锤体。它们还形成了分裂腔，一种无卵黄的薄结构，被认为在诱导分裂沟中起重要作用。在胚胎暴露于长春花碱（一种著名的微管抑制剂）的实验中也得到了基本相同的结果：将胚胎暴露于20 μg/mL长春花碱会导致卵裂球的分裂完全受到抑制，纺锤体和星体的形成均被完全抑制。相比之下，将胚胎暴露于5 μg/mL长春花碱时，尽管未检测到星体，但卵裂球的分裂并未受到阻止，同时形成了相当正常的纺锤体。因此，在非洲爪蟾早期胚胎的卵裂球中，正常纺锤体而非星体的形成与细胞分裂沟和分裂腔的形成之间存在密切相关性。我们认为，虽然纺锤体起着至关重要的作用，但在诱导像非洲爪蟾早期胚胎卵裂球这样的非常大的细胞的分裂沟方面，星体可能只起可有可无的作用。
