DISTRIBUTION OF GROWTH-ASSOCIATED CLASS-I ALPHA-TUBULIN AND CLASS-II BETA-TUBULIN MESSENGER-RNAS IN ADULT-RAT BRAIN

A comprehensive survey of class I alpha-tubulin (alpha 1) and class II beta-tubulin (beta II) mRNAs was performed using in situ hybridizatio n in order to determine the extent of continued expression of these im mature tubulin isotype mRNAs in the adult rat brain. Qualitatively sim ilar distributions of the two isotype mRNAs were observed, with marked variations in hybridization intensity of both probes apparent across different brain regions. Neurons in a wide variety of structures throu ghout the brain exhibited intense hybridization signals. While the pre sence of large numbers of neurons with a moderate hybridization intens ity could account for the relatively high level of total binding in so me regions such as the cerebellar and dentate granule layers, in most cases higher regional mRNA levels reflected greater hybridization inte nsity per neuron. Little variability in hybridization intensity was ty pically seen between individual cells within specific nuclei throughou t the brain. The presence of occasional intensely labeled neurons scat tered throughout the basal ganglia provided the most striking exceptio n to this pattern. While no qualitative differences between the distri butions of alpha 1-tubulin and beta II-tubulin mRNAs were observed, co nsistent differences in the relative intensity of hybridization for cY 1-tubulin versus beta II-tubulin mRNA were apparent in a few brain reg ions. Expression by glia did not appear to contribute significantly to detectable levels of either alpha 1-tubulin or beta II-tubulin mRNA. These findings suggest that continued expression of growth-associated tubulin isotype mRNAs may have functional significance in specific neu ronal populations of the adult brain. Partial overlap between the dist ributions of alpha 1- and beta II-tubulin mRNAs and that of GAP-43 mRN A is discussed, as are potential roles for growth-associated tubulin g ene expression in supporting cytoskeletal turnover, reactive axonal gr owth, and dendritic remodeling in the adult brain. (C) 1995 Wiley-Liss , Inc.