To study roles of the myelin basic protein (mbp) gene products in nervous system development, cDNA cloning and expression analyses were performed in Xenopus laevis. We cloned cDNAs for XMBP.1 and XMBP.2 encoded by xmbp.1 and xmbp.2 genes, respectively. We also identified xmbp.1 gene transcripts encoding three XGolli (X.laevis gene of the oligodendrocyte lineage) proteins, XBG21.1, XJ37.1, and XTP8.1, which are homologues of mouse BG21, J37, and TP8, respectively. In reverse transcription-polymerase chain reaction (RT-PCR) analyses, the XMBP, XJ37, and XTP8 mRNAs were expressed in brain, ovaries, testes, and/or thymus in frogs and in larvae after hatching. In contrast, the XBG21 mRNA was found fairly ubiquitously in adult tissues, unfertilized eggs and embryos throughout the developmental stages examined. Western blot analyses using three different monoclonal antibodies (mAbs) showed that the central and peripheral myelin contained 20kDa and18.5 kDa XMBP variants. In addition, XMBP was found in thymus by Western blotting and in thymocyte cytoplasm immunocytochemically. However, the XGolli protein, most provably XBG21, was detectable only in testes. The results indicate that the structure of xmbp gene products seems highly conserved among amphibians and mammals, although their expression patterns and thus physiological roles may partially differ. This is the first report that systematically describes the mbp gene products in nonmammalian vertebrates.
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