A family of splice variants of CstF-64 expressed in vertebrate nervous systems

Background: Alternative splicing and polyadenylation are important mechanisms for creating the proteomic diversity necessary for the nervous system to fulfill its specialized functions. The contribution of alternative splicing to proteomic diversity in the nervous system has been well documented, whereas the role of alternative polyadenylation in this process is less well understood. Since the CstF-64 polyadenylation protein is known to be an important regulator of tissue-specific polyadenylation, we examined its expression in brain and other organs. Results: We discovered several closely related splice variants of CstF-64 - collectively called beta CstF-64 - that could potentially contribute to proteomic diversity in the nervous system. The beta CstF-64 splice variants are found predominantly in the brains of several vertebrate species including mice and humans. The major beta CstF-64 variant mRNA is generated by inclusion of two alternate exons (that we call exons 8.1 and 8.2) found between exons 8 and 9 of the CstF-64 gene, and contains an additional 147 nucleotides, encoding 49 additional amino acids. Some variants of beta CstF-64 contain only the first alternate exon (exon 8.1) while other variants contain both alternate exons (8.1 and 8.2). In mice, the predominant form of beta CstF-64 also contains a deletion of 78 nucleotides from exon 9, although that variant is not seen in any other species examined, including rats. Immunoblot and 2D-PAGE analyses of mouse nuclear extracts indicate that a protein corresponding to beta CstF-64 is expressed in brain at approximately equal levels to CstF-64. Since beta CstF-64 splice variant family members were found in the brains of all vertebrate species examined (including turtles and fish), this suggests that beta CstF-64 has an evolutionarily conserved function in these animals. beta CstF-64 was present in both pre- and post-natal mice and in different regions of the nervous system, suggesting an important role for beta CstF-64 in neural gene expression throughout development. Finally, experiments in representative cell lines suggest that beta CstF-64 is expressed in neurons but not glia. Conclusion: This is the first report of a family of splice variants encoding a key polyadenylation protein that is expressed in a nervous system-specific manner. We propose that beta CstF-64 contributes to proteomic diversity by regulating alternative polyadenylation of neural mRNAs.