ALPHA-INTERNEXIN IS THE ONLY NEURONAL INTERMEDIATE FILAMENT EXPRESSEDIN DEVELOPING CEREBELLAR GRANULE NEURONS

We have used immunocytochemistry and in situ hybridization to examine the distribution of neuronal intermediate filament proteins and their mRNAs in the developing mouse cerebellum. First, we demonstrate that a lpha-internexin is abundantly expressed in the developing cerebellum a nd is the only neuronal intermediate filament protein expressed in dev eloping, including migrating, granule neurons. Second, in granule neur on reaggregates in vitro, alpha-internexin is the only neuronal interm ediate filament protein highly expressed in the processes of the cultu red granule neurons. This in vitro observation is consistent with resu lts from immunocytochemistry acid in situ hybridization studies of dev eloping granule neurons in vivo, which suggest that alpha-internexin i s the major neuronal intermediate filament protein in developing granu le neurons. Finally, the neurofilament triplet proteins are expressed later, and coexist with alpha-internexin in other cells, including Pur kinje cells and interneurons in the mature mouse cerebellum. These cha nges in neuronal intermediate filament composition may regulate neuron al maturation and axonal stability in cerebellar development. Furtherm ore, alpha-internexin may play a key role in neurite outgrowth and the establishment of neuronal cytoarchitecture. (C) 1996 John Wiley & Son s, Inc.