Fjose A, Njølstad P R, Nornes S, Molven A, Krauss S
Department of Molecular Genetics, Institute of Medical Biology, University of Tromsø, Norway.
Mech Dev. 1992 Nov;39(1-2):51-62. doi: 10.1016/0925-4773(92)90025-f.
The Drosophila homeobox gene engrailed (en) is needed for correct embryonic development, and related sequences are active during vertebrate embryogenesis. Here we report the protein coding sequence and embryonic expression pattern of the zebrafish engrailed-2 gene (eng-2) which is directly homologous to En-2 in mice and Xenopus. The predicted zebrafish Eng-2 protein shares 65% overall identity to its Xenopus counterpart. In addition to the highly conserved homeodomain region, sequence conservation is present within three short stretches in the N-terminal region. The embryonic expression of the eng-2 gene was analysed by in situ hybridization to whole-mount embryos and tissue sections. Transcripts are first detected in two lateral bands at the 10-h stage, when epiboly is completed. Within the next 2 h of development, these two bands migrate and fuse at the midline. By the time the neural keel becomes visible (11-12 h), a transverse stripe of eng-2 expressing cells is seen at the presumptive midbrain-hindbrain boundary. Later this stripe becomes significantly compressed along the AP axis, and in 24-h embryos eng-2 transcripts are detected mainly in the posterior midbrain. In the hindbrain, eng-2 expression seems restricted to the primordium of the cerebellum. A second site of activity was observed in each somite where specific myotomal cells, the muscle pioneers, express eng-2. Our observations are discussed in relation to early regionalization of the central nervous system (CNS) and the generation of morphological borders.
果蝇同源异型框基因“engrailed”（en）对于正确的胚胎发育是必需的，并且相关序列在脊椎动物胚胎发生过程中具有活性。在此，我们报告斑马鱼engrailed-2基因（eng-2）的蛋白质编码序列及其胚胎表达模式，该基因与小鼠和非洲爪蟾中的En-2直接同源。预测的斑马鱼Eng-2蛋白与其非洲爪蟾对应物的总体一致性为65%。除了高度保守的同源结构域区域外，在N端区域的三个短片段中也存在序列保守性。通过对整装胚胎和组织切片进行原位杂交，分析了eng-2基因的胚胎表达情况。转录本首先在原肠胚形成完成时的10小时阶段在两条侧带中被检测到。在接下来的2小时发育过程中，这两条带迁移并在中线融合。当神经嵴可见时（11 - 12小时），在假定的中脑 - 后脑边界处可见一条表达eng-2的细胞横向条纹。随后这条条纹沿前后轴显著压缩，在24小时胚胎中，eng-2转录本主要在中脑后部被检测到。在后脑中，eng-2的表达似乎局限于小脑原基。在每个体节中还观察到第二个活性位点，特定的肌节细胞，即肌肉先驱细胞，表达eng-2。我们结合中枢神经系统（CNS）的早期区域化和形态边界的形成对我们的观察结果进行了讨论。
