Retroviral promoter-trap insertion into a novel mammalian septin gene expressed during mouse neuronal development

We have characterized a retroviral promoter-trap insertion into a novel mammalian septin gene, Sep3. Its predicted amino acid sequence shares significant homology to that of Saccharomyces cerevisiae CDC3, CDC10, CDC11, CDC12, the Drosophila genes Pnut, Sep1, Sep2, and the mammalian genes BH5, CDC10, Nedd5, Diff6, and Sep2, which are implicated in cytokinesis and cell polarity. Sep3 encodes a protein of 465 amino acids, and contains an evolutionary conserved ATP/GTP-binding motif, two coiled-coil domains, and a highly hydrophobic domain at the C terminus. Alkaline phosphatase reporter gene expression in transgenic embryos was first detected at E8.5 in the neural fold, and high levels of expression continued throughout embryogenesis in the neural tube and brain. In addition, a low level of transient expression was detected in the somites, gut, and branchial arches of mouse embryos. Overall, reporter gene expression recapitulated Sep3 mRNA expression during mouse embryogenesis. In adults, Sep3 transcripts were only detected in the brain and testis. Zoo blot analysis revealed that Sep3-related sequences exist in several vertebrate species including zebrafish, frog, chicken, mouse and human. Consistent with the retroviral insertion into the 3' UTR of the Sep3 gene, no obvious phenotypes associated with the promoter trap were detected in transgenic embryos or adult mice. In summary, we report the first isolation of a novel full-length Sep3 cDNA and extensive characterization of its expression during mouse embryogenesis and in adult tissues.