Differential expression of several neurospecific beta-tubulin mRNAs in the mouse brain during development.

The expression of alpha- and beta-tubulin mRNAs has been studied during mouse brain development by using in vitro translation and specific cDNA clone hybridization techniques. The results presented here indicate that about half of the isotubulins expressed in vivo by brain cells are directly encoded by mRNA, the other isotypes being of post-translational origin. Among the six brain beta-tubulin mRNAs detected after RNA size fractionation followed by in vitro translation, four (1.8a, 1.8c, 2.4 and 3.5 kb) appear to be uniquely expressed in brain, and very likely in neurons. These four beta-tubulin RNA transcripts are differently regulated during development. The 1.8a-kb mRNA, which codes for the neurospecific beta' 1-isotubulin, is expressed very early, whereas the 1.8c, 2.4 and 3.5-kb mRNAs, which all code for a beta 4-tubulin isotype, are all expressed later. We isolated a beta-tubulin cDNA clone which specifically hybridizes to the large, neural 3.5-kb mRNA. The two other ubiquitous tubulin mRNAs, 1.8b and 2.9 kb in length, both direct the synthesis of an electrophoretically distinct beta 3 isotype. These results support the idea that within the tubulin multigene family, distinct beta-tubulin isogenes could be specifically expressed at various steps of the neuronal differentiation, thus contributing to the isotubulin diversity and specificity observed in this cell type and possibly involved in the developmental changes of its structure and function.