Expression of the mRNA for ? Proteins During Brain Development and in Cultured Neurons and Astroglial Cells

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Abstract
Two .tau. cDNA probes of 1.6 and 0.3 kilobases (kb) have been used to study the expresion of the .tau. mRNAs during mouse brain development and in highly homogeneous primary cultures of neurons and astrocytes. (1) Whatever the stage, a 6-kb mRNA was detected with the two probes. In the astrocytes a 6-kb mRNA hybridized clearly only with the 1.6-kb probe. (2) During brain development the abundance of .tau. mRNA increases from a late fetal stage (-4 days) until birth, remains high until 6 days postnatal, and then markedly decreases to reach very low values in adulthood. Such a marked decrease in the abundance of .tau. mRNA parallels that of .alpha.-tubulin mRNA. These data suggest that: (1) depending on the stage of development and on the cell type (neurons or astrocytes) .tau. mRNAs of the same size encode several .tau. proteins differing in molecular weight: several .tau. proteins are expressed either during early stages of development (juvenile .tau. proteins of 48 kilodaltons) or in adulthood (mature .tau. proteins of 50-70 kilodaltons) or are specific of the astrocyte (83 kilodaltons). (2) The expression of the two major components of axonal microtubules, tubulin and .tau. proteins, seems to be developmentally coordinated.