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

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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