Blake K J, Myette G, Jack J
Department of Anatomy, University of Connecticut Health Center, Farmington, Connecticut, 06030, USA.
Dev Biol. 1998 Nov 1;203(1):177-88. doi: 10.1006/dbio.1998.9036.
Mutations in the genes rib and raw cause defects in the morphology of a number of tissues in homozygous mutant embryos. A variety of tubular epithelial tissues adopt a wide, round shape in mutants and dorsal closure fails. Cells of the normal tubular epithelia are columnar and wedge-shaped, and cells of the epidermis become elongated dorsoventrally as dorsal closure occurs. However, the cells of mutants are round or cuboidal in all of the tissues with mutant phenotypes, consistent with the hypothesis that the products of these genes are required for proper cell shape. Cytoskeletal defects, in particular, defects in myosin-driven contraction of the cortical actin cytoskeleton, could be responsible for the lack of specific cell shapes in mutant embryos. This possibility is supported by our observation that the intracellular localization of nonmuscle myosin to the leading edge of the dorsally closing epidermis is absent or reduced in rib and raw mutant embryos. In contrast, the band of actin that is also located at the leading edge is neither eliminated nor interrupted by either rib or raw mutations. Furthermore, mutations of zipper, the gene encoding the nonmuscle myosin heavy chain, exhibit mutant phenotypes in most of the same tissues affected by rib and raw, and many of the phenotypes are similar to those of rib and raw. Therefore, the products of rib and raw may be required for proper myosin-driven contraction of the actin cytoskeleton.
rib和raw基因的突变会导致纯合突变胚胎中许多组织的形态出现缺陷。多种管状上皮组织在突变体中呈现出宽而圆的形状，并且背侧闭合失败。正常管状上皮的细胞呈柱状和楔形，随着背侧闭合的发生，表皮细胞会在背腹方向上伸长。然而，在所有具有突变表型的组织中，突变体的细胞都是圆形或立方形的，这与这些基因的产物是细胞正常形态所必需的这一假设一致。细胞骨架缺陷，特别是肌球蛋白驱动的皮质肌动蛋白细胞骨架收缩缺陷，可能是突变胚胎中缺乏特定细胞形态的原因。我们观察到在rib和raw突变胚胎中，非肌肉肌球蛋白在背侧闭合表皮的前缘的细胞内定位缺失或减少，这一观察结果支持了这种可能性。相比之下，同样位于前缘的肌动蛋白带既没有被rib突变也没有被raw突变消除或中断。此外，编码非肌肉肌球蛋白重链的基因zipper的突变，在受rib和raw影响的大多数相同组织中表现出突变表型，并且许多表型与rib和raw的表型相似。因此，rib和raw的产物可能是肌动蛋白细胞骨架正常的肌球蛋白驱动收缩所必需的。
