, Volume 17, Issue 1, pp 59-70

A novel isoform of beta-spectrin II localizes to cerebellar Purkinje-cell bodies and interacts with neurofibromatosis type 2 gene product schwannomin

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We report the identification of a full-length novel β-spectrin II gene (βSpIIΣ2) in human brain. The βSpIIΣ2 gene has 32 exons encoding an actin-binding domain, followed by 17-spectrin repeats, and a short COOH-terminal regulatory region that lacks the Pleckstrin homology (PH) domain. Pair-wise sequence analysis showed an additional 36 and 28 amino acids located at the NH2 and COOH-terminal regions of βSpIIΣ2, respectively. Northern-blot analysis showed an abundant expression of βSpIIΣ2 transcripts in brain, lung, and kidney. Western-blot analysis confirmed the predicted ∼225 kD molecular size of βSpIIΣ2 protein in these same tissues. In brain, immunofluorescent staining revealed that βSpIIΣ2 was enriched in cerebellar neurons, with specific enrichment in Purkinje cell bodies, but not in dendrites. Of considerable interest, neurofibromatosis type 2 (NF2) gene product schwannomin was found to co-immunoprecipitate with βSpIIΣ2 in cultured Purkinje cells. These results suggest that βSpIIΣ2 may play an important role in the assembly of the specialized plasma membrane domain of Purkinje neurons and that schwannomin may be involved in actin-cytoskeleton organization by interacting with βSpIIΣ2.