Abdelilah S, Driever W
Massachusetts General Hospital and Harvard Medical School, Charlestown 02129, USA.
Dev Biol. 1997 Apr 1;184(1):70-84. doi: 10.1006/dbio.1997.8517.
Mechanisms that underlie the formation of the vertebrate body appear to be highly conserved between amphibia and teleosts. For teleosts, however, mesoderm induction and the establishment of dorsoventral polarity are poorly understood. In this study, we present an analysis of early pattern formation in the zebrafish maternal-effect mutation janus. This mutation frequently results in a separation of the cleavage stage blastoderm into two halves that undergo separate development until fusion occurs at the end of gastrulation. Here, we employ janus-mutant embryos to analyze the mechanisms of mesoderm formation and ventral specification in a teleost. Analysis of the expression of the panmesodermal marker no tail in janus-mutant embryos indicates that mesoderm induction depends on a marginal position. In an analysis of ventral specification, we show that the early expression of the ventral marker GATA-2 is confined to the area on both blastodermal halves opposite the dorsal shield region. Since, in janus-mutant embryos, the dorsal position is random with respect to the division plane bisecting the two blastodermal halves, a variety of dorsoventral asymmetries arise within individual embryos. In one constellation, the dorsal position is localized to the plane of bisection and two ventral positions develop at opposite ends of the blastodermal halves. Hence, ventral fates can be specified at any position around the blastodermal margins and are excluded from the dorsal position. The diblastodermic system of the janus-mutant embryo allows for the study of the interactions of dorsal and ventral determinants in varying spatial arrangements. We have studied pattern formation in dorsal half-blastoderms that contain the entire shield region but only a reduced ventrolateral marginal zone. As assessed by the presence of the most ventral cell type, blood, ventral specification within a dorsal half-blastoderm is not suppressed.
脊椎动物身体形成的潜在机制在两栖动物和硬骨鱼之间似乎高度保守。然而，对于硬骨鱼来说，中胚层诱导和背腹极性的建立却知之甚少。在本研究中，我们对斑马鱼母源效应突变体janus的早期模式形成进行了分析。这种突变经常导致卵裂期胚盘分裂成两半，这两半各自发育，直到原肠胚形成末期融合。在这里，我们利用janus突变体胚胎来分析硬骨鱼中胚层形成和腹侧特化的机制。对janus突变体胚胎中泛中胚层标记物no tail表达的分析表明，中胚层诱导依赖于边缘位置。在腹侧特化分析中，我们发现腹侧标记物GATA - 2的早期表达局限于胚盘两半与背盾区域相对的区域。由于在janus突变体胚胎中，背侧位置相对于平分两个胚盘半体的分裂平面是随机的，所以单个胚胎内会出现多种背腹不对称性。在一种组合中，背侧位置位于平分平面，两个腹侧位置在胚盘半体的相对两端发育。因此，腹侧命运可以在胚盘边缘周围的任何位置被指定，而背侧位置则被排除在外。janus突变体胚胎的双胚盘系统允许研究背侧和腹侧决定因素在不同空间排列中的相互作用。我们研究了包含整个盾区域但只有减少的腹外侧边缘区域的背半胚盘中的模式形成。通过最腹侧细胞类型血液的存在来评估，背半胚盘中的腹侧特化并未受到抑制。
