CHARACTERIZATION OF NEURONAL CELL-SPECIFIC RNA-BINDING PROTEINS IN THE DEVELOPMENT OF RETINA

神经元RNA结合蛋白在基因表达的转录后调控中发挥重要作用，如选择性剪接、RNA转运和局部翻译。到目前为止，已经描述了几个神经元RNA结合蛋白家族。例如，Hu蛋白已被确认为与肺小细胞癌相关的人类副肿瘤性脑神经病的自身抗原。HU蛋白的主要功能之一是通过与RNA稳定元件结合来调节mRNA的代谢。Nova-1被称为副肿瘤性眼阵挛-肌阵挛共济失调抗原，也是一种神经元特异性RNA结合蛋白，调节选择性剪接。最近，我们从人和大鼠的cDNA文库中克隆了PTB的同源物，作为癌症相关性视网膜病变的可能的自身抗原。这一新蛋白被命名为PTB样蛋白(PTBLP)。在这项研究中，PTBLP在PC12细胞和PTBLP缺失小鼠的神经元分化中可能的作用进行了研究。杜里·…NGF更多地诱导PC12细胞分化，pTBLP-L(长形)基因表达下调。将PTBLP-L基因导入PC12细胞后，细胞分化受到抑制。然而，在PTBLP-S(短型；缺乏RNA结合能力)转基因细胞中，这种抑制作用并不明显。当PTBLP-L和PTBLP-S共转染时，PTBLP-L的抑制作用减弱。在分化细胞中，PTBLP-S定位于胞核，PTBLP-L散在分布于胞浆和神经元生长锥内。这些发现表明，PTBLP-L是神经元分化的负调控因子，而PTBLP-S是PTBLP-L的竞争对手。为了探讨PTBLP在完整动物中的功能，我们承诺通过同源重组敲除PTBLP基因。PTBLP基因缺失小鼠在胚胎晚期死亡。PTBLP杂合子未发现异常表型。这些结果提示，PTBLP在神经元发育过程中可能起重要作用。较少

Neuronal RNA-binding proteins play an important role in post-transcriptional regulation of gene expression such as alternative splicing, RNA transport and local translation. Several families of neuronal RNA-binding proteins have been so far described. For example, Hu proteins have been identified as an autoantigen of human paraneoplastic encephaloneuropathies associated with lung small cell carcinomas. One of the major functions of Hu proteins is regulation of mRNA metabolism through binding to RNA stability elements. Nova-1, known as the paraneoplastic opsoclonus-myoclonus ataxia antigen, is also a neuron-specific RNA binding protein that regulates alternative splicing. Recently, we have cloned a homologue of PTB as a possible autoantigen of cancer-associated retinopathy from human and rat cDNA libraries. This new protein was named as PTB-like protein (PTBLP).In this study, the possible roles of PTBLP on neuronal differentiation were examined using PC12 cells and PTBLP null mice. Duri … More ng NGF-induced neuronal differentiation in PC12 cells, PTBLP-L (long form) was down-regulated. By transfection of PTBLP-L into PC12 cells, the neuronal differentiation was suppressed. In PTBLP-S (short form ; lack the RNA binding ability) transfected cells, however, this suppression was not evident. When both PTBLP-L and PTBLP-S were co-transfected, the suppressive effect of PTBLP-L decreased. In differentiated cells, PTBLP-S localized in the nucleus and PTBLP-L was found dispersed throughout the cytoplasm and neuronal growth cone. These findings suggest that PTBLP-L acts as a negative regulator of neuronal differentiation and PTBLP-S acts as a competitor of PTBLP-L. To explore the functions of PTBLP in the intact animal, we undertook to knock out the PTBLP gene in mice by homologous recombination. PTBLP null mice were died in embryonic late stage. There was no abnormal phenotype in PTBLP heterozygotes. Those results are suggested that PTBLP may play an important role in neuronal development. Less