Department of Biology, University of York, York, United Kingdom.
PLoS One. 2010 Mar 10;5(3):e9610. doi: 10.1371/journal.pone.0009610.
Interest in establishing the basis of left/right asymmetry during embryogenesis has burgeoned in recent years. Relevant studies in mammals, focused largely on the mouse, have revealed involvement of a variety of genes that are common to the process in other animals. In the mouse, lateral differences in gene expression are first evident late in gastrulation when directional rotation of nodal cilia has been implicated in effecting the normally very strong bias in handedness. Reconstructing cleavage stages with correspondingly positioned blastomeres from appropriate numbers of conceptuses with similar division planes provides a way of testing whether they differ in potency without the confounding effects of reduced cell number. In a study using this strategy, 4-cell stage conceptuses reconstructed from blastomeres produced by equatorial as opposed to meridional second cleavage were found to be compromised in their ability to support normal development. Here, in more refined reconstructions undertaken at both the 4- and 8-cell stage, no significant impairment of development to the 9(th) or 12(th) day of gestation was found for products of equatorial second cleavage or their 8-cell stage progeny. Most surprisingly, however, a significant increase in reversal of the direction of axial rotation was found specifically among fetuses developing from conceptuses reconstructed from 8-cell stage progeny of products of equatorial second cleavage. Hence, manipulations during early cleavage some 6 days before fetal asymmetries are first evident can perturb the normally very strong bias in specification of a facet of left-right asymmetry.
近年来，人们对胚胎发生过程中建立左右不对称基础的兴趣日益浓厚。在哺乳动物中的相关研究主要集中在老鼠身上，这些研究揭示了许多基因的参与，这些基因在其他动物的过程中是共同的。在老鼠中，基因表达的侧向差异在原肠胚晚期首先出现，此时，节点纤毛的定向旋转被认为对惯用手的强烈偏向起作用。从具有相似分裂平面的适当数量的胚胎中重建具有相应位置的分裂球的卵裂阶段，提供了一种在没有细胞数量减少的混杂效应的情况下测试它们在效力上是否不同的方法。在使用这种策略的一项研究中，发现从赤道而非子午第二次分裂产生的分裂球重建的 4 细胞期胚胎在支持正常发育的能力上受到损害。在这里，在 4 细胞期和 8 细胞期进行的更精细的重建中，对于赤道第二次分裂的产物或其 8 细胞期后代，没有发现对妊娠第 9 天或第 12 天的发育有显著的损害。然而，最令人惊讶的是，在专门从赤道第二次分裂产物的 8 细胞期后代重建的胚胎中，轴向旋转方向的反转明显增加。因此，在胎儿不对称性首次出现之前大约 6 天的早期卵裂期间进行的操作可以干扰左右不对称特定方面的指定的强烈偏向。
