DIFFERENTIAL REGULATION OF BETA-III AND OTHER TUBULIN GENES DURING PERIPHERAL AND CENTRAL NEURON DEVELOPMENT

Mammalian peripheral and central neurons differ considerably in the composition and properties of their axonal cytoskeletons. Recent reports of the selective expression of a high molecular weight (HMW) tau protein in neurons with peripherally projecting axons have furthered the idea that the microtubules in central and peripheral neurons are disparate. In the present study, we examined the possibility that the various tubulin genes are differentially expressed in central versus peripheral neurons. To examine this, we compared the expression of four of the beta-tubulin mRNAs (classes beta(I), beta(II), beta(III), beta(IV)) and the alpha1-tubulin mRNA in rat dorsal root ganglion (DRG) neurons with their expression in cerebral cortex during postnatal development (P5-90), using northern blots and in situ hybridization. We document both similarities and differences in tubulin gene expression in these two regions of the neuraxis during postnatal development. In both DRG and cortex, the expression of the class beta(I)- and beta(II)-tubulin mRNAs and the alpha1-tubulin mRNA was higher at earlier stages of postnatal development than in the adult. However, class beta(IV)-tubulin mRNA levels increased during cortical development but decreased during DRG postnatal development. The opposite pattern was found for the neuron-specific class beta(III)-tubulin gene, the mRNA levels of which were high in cortex, at birth and then decreased with increasing postnatal development. In DRG, the beta(III)-tubulin mRNA levels generally increased during postnatal development. Beta(III)-tubulin protein levels were examined qualitatively at different developmental stages (5-90 days) by immunoblotting and immunocytochemistry. These studies showed a robust reduction in beta(III)-tubulin levels from P5 to adult stages in cortex, but a more complex pattern of change in the DRG. The results suggest that differential utilization of the tubulin gene products exists in central and peripheral nervous tissue and that this may play a role in specifying differences in the functional properties of neuronal cytoskeletons in these regions.