Solnica-Krezel L
Department of Molecular Biology, Vanderbilt University, Nashville, Tennessee 37232, USA.
Curr Top Dev Biol. 1999;41:1-35. doi: 10.1016/s0070-2153(08)60268-9.
Vertebrate embryos, despite quite diverse early morphologies, appear to employ similar cellular strategies and conserved biochemical pathways in their development (Eyal-Giladi, 1997). In the past decade, a small tropical teleost, zebrafish (Danio rerio), became an important model system in which to study development (Streisinger et al., 1981). By combining embryology with molecular and classical genetic methods, our understanding of early inductive and morphogenetic events during vertebrate embryogenesis significantly advanced. In zebrafish, dorsal-ventral polarity is established during early cleavage and is dependent on microtubular transport of determinants from the vegetal pole to the blastomeres positioned on top of the yolk cell. The syncytium forming from these marginal blastomeres in the early blastula exhibits dorsal-ventral asymmetry with beta-catenin localized to the nuclei on the presumptive dorsal side of the syncytium. The yolk cell is a source of signals that induce and pattern overlying blastoderm. Therefore, the dorsal yolk syncytial layer is equivalent to the Nieuwkoop center of the amphibian embryo. The embryonic shield, a thickening of the dorsal blastoderm margin, exhibits properties similar to the amphibian Spemann organizer. However, certain inductive and patterning signals from the organizer might be produced before the shield forms or might originate outside of the shield. Similar to the amphibian embryo, the key patterning functions of the fish dorsal organizer (i.e., dorsalization of mesoderm, ectoderm, and coordination of gastrulation movements) are performed by secreted molecules that antagonize the ventralizing activity of the swil (zbmp-2) and zbmp-4 gene products expressed on the ventral side of the embryo. These functions of the dorsal organizer require the activity of the chordino gene (a zebrafish homologue of chordin), bozozok, mercedes and ogon loci.
脊椎动物胚胎尽管早期形态差异很大，但在发育过程中似乎采用了相似的细胞策略和保守的生化途径（Eyal-Giladi，1997）。在过去十年中，一种小型热带硬骨鱼——斑马鱼（Danio rerio），成为了研究发育的重要模型系统（Streisinger等人，1981）。通过将胚胎学与分子和经典遗传学方法相结合，我们对脊椎动物胚胎发生过程中早期诱导和形态发生事件的理解有了显著进展。在斑马鱼中，背腹极性在早期卵裂过程中建立，并且依赖于决定因子从植物极到位于卵黄细胞顶部的卵裂球的微管运输。在早期囊胚中，由这些边缘卵裂球形成的合胞体表现出背腹不对称，β-连环蛋白定位于合胞体假定背侧的细胞核中。卵黄细胞是诱导和塑造覆盖其上的胚盘的信号来源。因此，背侧卵黄合胞体层等同于两栖动物胚胎的Nieuwkoop中心。胚胎盾，即背侧胚盘边缘的增厚部分，表现出与两栖动物Spemann组织者相似的特性。然而，来自组织者的某些诱导和模式形成信号可能在盾形成之前就已产生，或者可能起源于盾之外。与两栖动物胚胎类似，鱼类背侧组织者的关键模式形成功能（即中胚层、外胚层的背化以及原肠胚形成运动的协调）是由分泌分子执行的，这些分子拮抗在胚胎腹侧表达的swil（zbmp-2）和zbmp-4基因产物的腹化活性。背侧组织者的这些功能需要chordin基因（chordin的斑马鱼同源物）、bozozok、mercedes和ogon基因座的活性。
