Dush M K, Martin G R
Department of Anatomy and Developmental Biology Program, School of Medicine, University of California, San Francisco 94143.
Dev Biol. 1992 May;151(1):273-87. doi: 10.1016/0012-1606(92)90232-6.
Two mouse genes, Evx-1 and Evx-2, each encoding a homeodomain closely related to that of the Drosophila even-skipped gene were isolated using a PCR-based strategy. The structure and sequence of these genes are described. Mapping studies localized Evx-1 to chromosome 6, near the Hox-1 gene cluster, and Evx-2 to chromosome 2, near the Hox-4 cluster. The evolutionary implications of these linkages are discussed. RNA in situ hybridization analysis of Evx expression in embryos demonstrated a striking pattern of Evx-1 expression during gastrulation, whereas Evx-2 RNA could not be detected at any stage by this technique. Evx-1 RNA is first detected shortly before the onset of gastrulation in a region of ectoderm containing cells that will soon be found in the primitive streak. This localized expression of Evx-1 provides the first molecular evidence for regional differences in the mouse embryonic ectoderm before gastrulation. Throughout gastrulation, Evx-1 expression is limited to cells near and within the streak and that expression is graded, with a posterior-to-anterior decrease in the level of RNA. Based on fate-mapping studies indicating that different types of mesoderm emerge from different regions of the primitive streak and our observation that high levels of expression are localized to the region that will give rise to extraembryonic and ventral mesoderm, we speculate that Evx-1 plays a role in the dorsoventral specification of mesodermal cell fate.
利用基于聚合酶链反应（PCR）的策略分离出了两个小鼠基因，Evx - 1和Evx - 2，它们各自编码一种与果蝇的even - skipped基因的同源结构域密切相关的同源结构域。描述了这些基因的结构和序列。定位研究将Evx - 1定位于6号染色体上，靠近Hox - 1基因簇，将Evx - 2定位于2号染色体上，靠近Hox - 4基因簇。讨论了这些连锁关系的进化意义。对胚胎中Evx表达的RNA原位杂交分析表明，在原肠胚形成过程中Evx - 1呈现出显著的表达模式，而通过该技术在任何阶段都检测不到Evx - 2的RNA。Evx - 1 RNA最早在原肠胚形成开始前不久，在外胚层的一个区域被检测到，该区域的细胞很快会出现在原条中。Evx - 1的这种局部表达为原肠胚形成前小鼠胚胎外胚层的区域差异提供了首个分子证据。在整个原肠胚形成过程中，Evx - 1的表达仅限于原条附近和内部的细胞，且这种表达是梯度性分布的，RNA水平从后向前逐渐降低。基于命运图谱研究表明不同类型的中胚层从原条的不同区域产生，以及我们观察到高水平表达定位于将产生胚外和腹侧中胚层的区域，我们推测Evx - 1在中胚层细胞命运的背腹向特化中发挥作用。
