Taira M, Hayes W P, Otani H, Dawid I B
Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
Dev Biol. 1993 Sep;159(1):245-56. doi: 10.1006/dbio.1993.1237.
The Xenopus LIM class homeobox gene Xlim-3 was identified initially as a fragment isolated by polymerase chain reaction cloning with an embryonic cDNA library as template (Taira et al., 1992, Genes Dev. 6, 356-366). cDNA clones representing most of the Xlim-3 mRNA were isolated from an adult brain library. The predicted Xlim-3 protein contains two copies of the LIM domain, a homeodomain, and a C-terminal region rich in proline, glycine, and serine. RNA blot hybridization showed that Xlim-3 mRNA is detected in dorsal regions at neural tube and tailbud stages and in adults predominantly in the pituitary gland and weakly in the eye and brain. Whole mount in situ hybridization revealed that Xlim-3 mRNA is first detectable at the neural plate stage in the stomodeal-hypophyseal (pituitary) anlage and in the neural plate where labeled cells were found adjacent to the forming floor plate. In situ hybridization analysis on serial sections at later stages showed that embryonic Xlim-3 expression persists in the pituitary and pineal, as well as in some cells of the retina, hindbrain, and spinal cord. In the retina, Xlim-3 mRNA was only detected in a distinct sublamina of the inner nuclear layer, but not in dividing cells of ciliary margin. This discrete manner of Xlim-3 expression, especially persistent expression in the pituitary (before morphogenesis of the gland to adult), supports a role in the specification and maintenance of differentiation of distinct neuronal and neuroendocrine tissues.
非洲爪蟾LIM类同源框基因Xlim-3最初是作为一个通过聚合酶链反应克隆分离得到的片段被鉴定出来的，该反应以胚胎cDNA文库为模板（Taira等人，1992年，《基因与发育》6卷，356 - 366页）。代表大部分Xlim-3 mRNA的cDNA克隆是从成体脑文库中分离得到的。预测的Xlim-3蛋白包含两个LIM结构域拷贝、一个同源结构域以及一个富含脯氨酸、甘氨酸和丝氨酸的C末端区域。RNA印迹杂交显示，在神经管和尾芽阶段的背侧区域以及成体中能检测到Xlim-3 mRNA，在成体中主要存在于垂体，在眼睛和脑中表达较弱。整体原位杂交显示，Xlim-3 mRNA最早在神经板阶段的口凹 - 垂体原基以及神经板中可检测到，在那里发现标记细胞与形成中的底板相邻。对后期连续切片的原位杂交分析表明，胚胎期Xlim-3的表达在垂体和松果体以及视网膜、后脑和脊髓的一些细胞中持续存在。在视网膜中，Xlim-3 mRNA仅在内核层的一个特定亚层中检测到，而在睫状缘的分裂细胞中未检测到。Xlim-3这种离散的表达方式，尤其是在垂体中的持续表达（在腺体发育为成体之前），支持了它在特定神经元和神经内分泌组织的分化特化及维持过程中发挥作用。
