Toyama R, Curtiss P E, Otani H, Kimura M, Dawid I B, Taira M
Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
Dev Biol. 1995 Aug;170(2):583-93. doi: 10.1006/dbio.1995.1238.
LIM homeobox genes are characterized by encoding proteins in which two cysteine-rich LIM domains are associated with a homeodomain. We report the isolation of a gene, named Xlim-5 in Xenopus and lim5 in the zebrafish, that is highly similar in sequence but quite distinct in expression pattern from the previously described Xlim-1/lim1 gene. In both species studied the lim5 gene is expressed in the entire ectoderm in the early gastrula embryo. The Xlim-5 gene is activated in a cell autonomous manner in ectodermal cells, and this activation is suppressed by the mesoderm inducer activin. During neurulation, expression of the lim5 gene in both the frog and fish embryo is rapidly restricted to an anterior region in the developing neural plate/keel. In the 2-day Xenopus and 24-hr zebrafish embryo, this region becomes more sharply defined, forming a strongly lim5-expressing domain in the diencephalon anterior to the midbrain-forebrain boundary. In addition, regions of less intense lim5 expression are seen in the zebrafish embryo in parts of the telencephalon, in the anterior diencephalon coincident with the postoptic commissure, and in restricted regions of the midbrain, hindbrain, and spinal cord. Expression in ventral forebrain is abolished from the 5-somite stage onward in cyclops mutant fish. These results imply a role for lim5 in the patterning of the nervous system, in particular in the early specification of the diencephalon.
LIM 同源框基因的特点是编码的蛋白质中含有两个富含半胱氨酸的 LIM 结构域，并与一个同源结构域相关联。我们报告了一个基因的分离情况，该基因在非洲爪蟾中命名为 Xlim-5，在斑马鱼中命名为 lim5，其序列与先前描述的 Xlim-1/lim1 基因高度相似，但表达模式却截然不同。在所研究的两个物种中，lim5 基因在原肠胚早期的整个外胚层中表达。Xlim-5 基因在外胚层细胞中以细胞自主方式被激活，而这种激活会被中胚层诱导因子激活素抑制。在神经胚形成过程中，lim5 基因在青蛙和鱼类胚胎中的表达迅速局限于发育中的神经板/龙骨的前部区域。在 2 天龄的非洲爪蟾和 24 小时龄的斑马鱼胚胎中，该区域变得更加清晰，在中脑-前脑边界前方的间脑中形成一个强表达 lim5 的结构域。此外，在斑马鱼胚胎中，在端脑的部分区域、与视交叉后连合一致的前间脑以及中脑、后脑和脊髓的特定区域中可以看到 lim5 表达较弱的区域。在独眼畸形突变鱼中，从 5 体节期开始腹侧前脑的表达就消失了。这些结果表明 lim5 在神经系统的模式形成中起作用，特别是在间脑的早期特化中。
