Conrad A H, Stephens A P, Conrad G W
Division of Biology, Kansas State University, Manhattan 66506, USA.
J Exp Zool. 1994 Jul 1;269(3):188-204. doi: 10.1002/jez.1402690304.
Some effects of gravity on early morphogenesis are correlated with microtubule locations within cells. During first cleavage in Ilyanassa obsoleta embryos, a transitory polar lobe constriction forms and then relaxes, allowing the polar lobe to merge with one daughter cell. If the polar lobe is equally divided or removed, morphogenesis is severely disrupted. To examine microtuble locations during early Ilyanassa development, eggs were fixed and stained for polymerized alpha-tubulin during first cleavage. The mitotic apparatus assembles at the animal pole. The cleavage furrow forms between the asters, constricting to a stabilized intercellular bridge encircling midbody-bound microtubules, whereas the polar lobe constriction forms below and parallel to the spindle, constricting to a transitory intercellular bridge encircling no detectable microtubules. At metaphase an alpha-tubulin epitope is distributed throughout the spindle, whereas a beta-tubulin epitope is present predominantly in the asters. Incubation in hexylene glycol, a drug that increases microtubule polymerization, during mitosis causes the polar lobe constriction to tighten around polymerized alpha-tubulin and remain stably constricted. If hexylene glycol is removed, alpha-tubulin staining disappears from the polar lobe constriction, which relaxes, whereas microtubules remain in the cleavage furrow, which remains constricted. These observations suggest that asymmetric distribution of microtubules affects early Ilyanassa cleavage patterns, and that continued presence of microtubules extending through an intercellular bridge is important for stabilization of the bridge constriction prior to completion of cytokinesis. These data provide the basis for further analysis of the role of microtubules in possible microgravity disruptions of Ilyanassa development.
重力对早期形态发生的一些影响与细胞内微管的位置相关。在过时泥蚶胚胎的第一次卵裂期间，一个短暂的极叶缢缩形成然后松弛，使极叶与一个子细胞融合。如果极叶被均等分割或去除，形态发生会严重受阻。为了研究泥蚶早期发育过程中微管的位置，在第一次卵裂期间将卵固定并用聚合的α - 微管蛋白进行染色。有丝分裂器在动物极组装。卵裂沟在星体之间形成，收缩形成围绕着与中体相连的微管的稳定细胞间桥，而极叶缢缩在纺锤体下方并与之平行形成，收缩形成围绕无可检测微管的短暂细胞间桥。在中期，一个α - 微管蛋白表位分布在整个纺锤体中，而一个β - 微管蛋白表位主要存在于星体中。在有丝分裂期间用己二醇（一种增加微管聚合的药物）孵育会导致极叶缢缩围绕聚合的α - 微管蛋白收紧并保持稳定缢缩。如果去除己二醇，α - 微管蛋白染色从极叶缢缩处消失，极叶缢缩松弛，而微管仍留在收缩的卵裂沟中。这些观察结果表明微管的不对称分布影响泥蚶早期的卵裂模式，并且延伸穿过细胞间桥的微管的持续存在对于在胞质分裂完成之前稳定桥缢缩很重要。这些数据为进一步分析微管在泥蚶发育可能的微重力干扰中的作用提供了基础。
