EXPRESSION OF THE GENE FOR THE NEURONAL INTERMEDIATE FILAMENT PROTEINALPHA-INTERNEXIN COINCIDES WITH THE ONSET OF NEURONAL DIFFERENTIATIONIN THE DEVELOPING RAT NERVOUS-SYSTEM

While neurofilaments have long been considered early markers of neuron al differentiation, they cannot be detected in most newly postmitotic neurons of the developing central nervous system (CNS). Here we show t hat these neurons already express the neuronal intermediate filament p rotein alpha-internexin at high levels. alpha-internexin is expressed by most, if not all, neurons as they begin differentiation and shows n o overlap with vimentin, whose expression in the CNS is restricted to mitotic neuronal precursors. In the adult, alpha-internexin is the onl y intermediate filament gene expressed by the cerebellar granule cells , the source of the thin-caliber parallel fibers; conversely, neurofil ament proteins are highly expressed in large neurons, which express al pha-internexin at low levels. These data suggest that neuronal interme diate filaments may regulate axonal stability and/or diameter through changes not only in their number, but also in their subunit compositio n. (C) 1994 Wiley-Liss, Inc.