Shih J, Keller R
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Development. 1992 Dec;116(4):915-30. doi: 10.1242/dev.116.4.915.
In a companion paper (Shih, J. and Keller, R. (1992) Development 116, 901-914), we described a sequence of cell behaviors, called mediolateral intercalation behavior (MIB), that produces mediolateral cell intercalation, the process that drives convergence and extension of the axial and paraxial mesoderm of Xenopus. In this paper, we describe the pattern of expression of MIB in the mesoderm during gastrulation, using video image processing and recording of cell behavior in 'shaved', open-faced explants of the marginal zone. At midgastrula stage (10.5), MIB begins at two dorsolateral sites in the prospective anterior mesoderm and progresses medially along two arcs that lengthen toward and meet at the midline to form a single arc of cells expressing MIB, called the vegetal alignment zone (VgAZ). The notochordal-somitic mesodermal boundary forms within the VgAZ at stage 11, and then progresses animally and laterally, along the prospective anterior-posterior axis, eventually bounding a trapezoidal area the shape of the fate-mapped notochord. Meanwhile, from its origin in the VgAZ, MIB spreads in the prospective posterior direction along the lateral boundaries of both the notochordal and somitic mesoderm. From there it spreads medially in both tissues. Subsequently, vacuolation of notochord cells, and segmentation and expression of a somite-specific marker repeat the progression of mediolateral intercalation behavior. Thus cells in the posterior, medial regions of the notochordal and the somitic territories are the last to express mediolateral intercalation behavior and subsequent tissue differentiations. In explants that do not converge, these cells neither express mediolateral intercalation behavior nor differentiate. These facts suggest that progressions of MIB in the anterior-posterior and lateral-medial directions may be organized by signals emanating from the lateral somitic and notochordal boundaries. These signals may have limited range and may be dependent on convergence, driven by mediolateral cell intercalation, to bring cells within their range. In the embryo, the posterior progression of MIB results in arcs of convergence, anchored in the vegetal endoderm at each end, acting on the inside of the blastoporal lip to produce involution of the IMZ.
在一篇配套论文中（施，J. 和凯勒，R.（1992年）《发育》116卷，901 - 914页），我们描述了一系列细胞行为，称为中外侧插入行为（MIB），这种行为产生中外侧细胞插入，该过程驱动非洲爪蟾轴旁中胚层和轴中胚层的汇聚和延伸。在本文中，我们利用视频图像处理以及对边缘区“刮除”的、无覆盖物外植体中细胞行为的记录，描述了原肠胚形成过程中MIB在中胚层中的表达模式。在原肠胚中期（10.5期），MIB在前侧中胚层的两个背外侧位点开始，并沿着两条弧线向内侧推进，这两条弧线朝着中线延长并在中线处汇合，形成一条表达MIB的细胞单弧线，称为植物对齐区（VgAZ）。脊索 - 体节中胚层边界在11期于VgAZ内形成，然后沿着预期的前后轴向动物极和外侧推进，最终界定出一个梯形区域，其形状为命运图谱中的脊索形状。与此同时，从其在VgAZ的起始点开始，MIB沿着脊索和体节中胚层的外侧边界向预期的后侧方向扩散。从那里它在这两个组织中向内侧扩散。随后，脊索细胞的空泡化以及体节特异性标记物的分割和表达重复了中外侧插入行为的进程。因此，脊索和体节区域后侧、内侧的细胞是最后表达中外侧插入行为及随后组织分化的细胞。在不发生汇聚的外植体中，这些细胞既不表达中外侧插入行为也不发生分化。这些事实表明，MIB在前后方向和内外侧方向的进程可能是由体节和脊索外侧边界发出的信号所组织的。这些信号可能范围有限，并且可能依赖于由中外侧细胞插入驱动的汇聚，将细胞带入其作用范围内。在胚胎中，MIB的后侧进程导致汇聚弧线，其两端锚定在植物内胚层，作用于胚孔唇内部以产生内胚层边缘带（IMZ）内陷。
