Cell motility driving mediolateral intercalation in explants of Xenopus laevis.
Cell motility driving mediolateral intercalation in explants of Xenopus laevis.
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作者：
J. Shih;R. Keller
在非洲爪蛙中，中胚层深层细胞沿着内侧轴相互活跃地嵌入(内侧细胞嵌入)，形成更窄、更长的排列，从而产生会聚和延伸。推动这种嵌入的细胞运动性还知之甚少。一篇配套的论文显示，内胚层上皮组织紧邻其下的最外层的中胚层细胞经历汇聚和延伸，并且其他证据表明，这些深层细胞是中外侧插层中最活跃的参与者(Shih，J.和Keller，R.(1992)Development 116,887-899)。在本文中，我们刮掉了中胚层细胞的更深层，这使得我们能够用高分辨率视频显微镜观察到靠近组织上皮的中胚层细胞的突起活动。这些中胚层细胞在原肠胚早期分裂，表现出快速的、随机定向的突起活动。在中肠胚早期，它们开始表现出一系列特有的行为，称为内侧插入行为(MIB)：(1)在外侧和内侧方向形成大的、稳定的、丝状和片状的突起，从而使细胞两极；(2)这些突起直接作用于相邻的细胞表面并对其施加牵引力，而不受接触抑制；(3)结果是，细胞伸长并平行于内侧轴排列；(4)细长的排列的细胞沿着内侧轴相互插入，从而形成更长、更窄的阵列。在第10.5阶段制作的基本上是单层深层中胚层细胞的外植体，通过中间外侧嵌入而汇聚和延伸。因此，到10.5阶段(中胃期早期)，MIB在中胚层深层细胞中的表达在生理和机械上独立于内胚层上皮细胞的组织影响(Shih，J.和Keller，R.(1992)Development 116 887-899)，并且是支持体轴中外侧嵌入和会聚和延伸的基本细胞运动。
In Xenopus, convergence and extension are produced by active intercalation of the deep mesodermal cells between one another along the mediolateral axis (mediolateral cell intercalation), to form a narrower, longer array. The cell motility driving this intercalation is poorly understood. A companion paper shows that the endodermal epithelium organizes the outermost mesodermal cells immediately beneath it to undergo convergence and extension, and other evidence suggests that these deep cells are the most active participants in mediolateral intercalation (Shih, J. and Keller, R. (1992) Development 116, 887-899). In this paper, we shave off the deeper layers of mesodermal cells, which allows us to observe the protrusive activity of the mesodermal cells next to the organizing epithelium with high resolution video microscopy. These mesodermal cells divide in the early gastrula and show rapid, randomly directed protrusive activity. At the early midgastrula stage, they begin to express a characteristic sequence of behaviors, called mediolateral intercalation behavior (MIB): (1) large, stable, filiform and lamelliform protrusions form in the lateral and medial directions, thus making the cells bipolar; (2) these protrusions are applied directly to adjacent cell surfaces and exert traction on them, without contact inhibition; (3) as a result, the cells elongate and align parallel to the mediolateral axis and perpendicular to the axis of extension; (4) the elongate, aligned cells intercalate between one another along the mediolateral axis, thus producing a longer, narrower array. Explants of essentially a single layer of deep mesodermal cells, made at stage 10.5, converge and extend by mediolateral intercalation. Thus by stage 10.5 (early midgastrula), expression of MIB among deep mesodermal cells is physiologically and mechanically independent of the organizing influence of the endodermal epithelium, described previously (Shih, J. and Keller, R. (1992) Development 116 887-899), and is the fundamental cell motility underlying mediolateral intercalation and convergence and extension of the body axis.