Henry J Q, Martindale M Q
Department of Cell and Structural Biology, University of Illinois, Urbana, Illinois, 61801, USA.
Dev Biol. 1996 Dec 15;180(2):713-21. doi: 10.1006/dbio.1996.0340.
Experiments were performed to determine whether the first cleavage division plays a role in setting up the dorsoventral axis in embryos of the equal-cleaving nemertean Cerebratulus lacteus. Fertilized eggs were compressed to change the orientation of the first cleavage spindle, and thus the plane of the first cleavage division. One cell of the resulting two-celled embryos was then injected with lineage tracer to determine whether the first cleavage plane always maintains its normal relationships to the median and frontal planes or whether new relationships (and thus, novel cell lineages) could be created. Many of these compressed embryos gave rise to normal-appearing pilidium larvae in which the first cleavage plane had taken on various oblique angular relationships relative to the plane of bilateral symmetry and the dorsoventral axis of the larva. These findings indicate that the first cleavage plane can be dissociated from its normal relationships to these axial properties. Thus, the first cleavage division is not causally involved in the establishment of the dorsoventral and bilateral axes. We argue that the dorsoventral axis is specified prior to the first cleavage division.
进行了实验以确定第一次卵裂是否在等裂纽形动物乳酸脑纹虫胚胎的背腹轴建立中起作用。受精卵被压缩以改变第一次卵裂纺锤体的方向，从而改变第一次卵裂的平面。然后向所得二细胞胚胎的一个细胞中注射谱系示踪剂，以确定第一次卵裂平面是否始终保持其与中线和额面的正常关系，或者是否可以建立新的关系（从而产生新的细胞谱系）。许多这些压缩胚胎发育成外观正常的担轮幼虫，其中第一次卵裂平面相对于幼虫的双侧对称平面和背腹轴呈现出各种倾斜角度关系。这些发现表明，第一次卵裂平面可以与其与这些轴向特性的正常关系分离。因此，第一次卵裂与背腹轴和双侧轴的建立没有因果关系。我们认为背腹轴在第一次卵裂之前就已确定。
