Genomic organisation and nervous system expression of radial spoke protein 3.

Following their generation in the germinal zones, young neurons of the neocortex, hippocampus and cerebellum undergo long-distance migration to reach their final destinations. This locomotive activity depends on active deployment of cytoskeletal elements including the microtubule apparatus. In this study, we report the identification and expression of radial spoke protein 3 (RSP3), a member of a protein cluster responsible for anchoring and modifying dynein motor activity known to be crucial to microtubule sliding. The mouse RSP3 gene consists of eight exons and seven introns and spans over 230 kb. The genomic organisations of the human and rat RSP3 genes are similar although they span approximately 23 and 53 kb, respectively. This is in contrast to the Chlamydomonas RSP3 gene, where RSP3 was first isolated, which consists of four exons and three introns and spans approximately 2.7 kb. Despite these differences, the nucleotide and amino acid sequences upstream of, and throughout the RPII-binding domain of RSP3 are highly conserved between all the above-mentioned species. Mouse RSP3 mRNA was restricted to the developing neocortex, hippocampus and cerebellum during the stages when these structures are known to contain large numbers of migratory neurons. Gene expression studies suggest that RSP3 function is consistent with a locomotory role for this protein in migrating young neurons. In addition, expression of RSP3 mRNA in adult neurons point to additional, though still unknown functions. Our data provides the first evidence for the expression of radial spoke proteins in higher eukaryotes, and provides a biological framework for how these proteins may participate in microtubule sliding and neuronal migration in the embryonic brain.