Septin Gene Research Articles

Reciprocal Expression of Infant- and Adult-Preferring Transcripts of CDCrel-1 Septin Gene in the Rat Neocortex

We report here the isolation and characterization of cDNA clones for a novel isoform of CDCrel-1 septin, termed CDCrel-1A, with a different 5′ end sequence from the transcripts encoding the known CDCrel-1 (designated as CDCrel-1F) in the developing rat neocortex. Alternative polyadenylation site selections resulted in various transcripts for CDCrel-1A including the fusion forms with another gene, platelet glycoprotein Ibβ (GPIbβ). Expression of the distinct transcripts encoding CDCrel-1A and CDCrel-1F increased and decreased, respectively, from the infant to adult period. Therefore CDCrel-1A might be a major form of the CDCrel-1 septin in the adult neocortex of mammals.

Cloning and expression studies during vegetative and sexual development of Pbs1, a septin gene homologue from Pyrenopeziza brassicae

A septin gene homologue designated Pyrenopeziza brassicae septin 1 ( Pbs1) has been identified and cloned from the plant pathogenic fungus Pyrenopeziza brassicae and its expression analysed. Pbs1 is present in both mating types and in a single copy within each genome and is transcribed in proportionate levels during both vegetative and sexual growth.

Sint1, a common integration site in SL3-3-induced T-cell lymphomas, harbors a putative proto-oncogene with homology to the septin gene family.

The murine retrovirus SL3-3 is a potent inducer of T-cell lymphomas when inoculated into susceptible newborn mice. Previously, DNAs from twenty SL3-3-induced tumors were screened by PCR for provirus integration sites. Two out of 20 tumors demonstrated clonal provirus insertion into a common region. This region has now been isolated and characterized. The region, named SL3-3 integration site 1 (Sint1), maps to the distal end of mouse chromosome 11, corresponding to human chromosome 17q25, and may be identical to a mouse mammary tumor virus integration site in a T-cell lymphoma, Pad3. Two overlapping genomic lambda clones spanning about 35 kb were isolated and used as a starting point for a search for genes in the neighborhood of the virus integration sites. A genomic fragment was used as a hybridization probe to isolate a 3-kb cDNA clone, the expression of which was upregulated in one of two tumors harboring a provirus in Sint1. The cDNA clone is predicted to encode a protein which shows 97.0% identity to a human septin-like protein encoded by a gene which has been found as a fusion partner gene of MLL in an acute myeloid leukemia with a t(11;17)(q23;q25). Together these findings raise the possibility that a proto-oncogene belonging to the septin family, and located about 15 kb upstream of the provirus integration sites, is involved in murine leukemia virus-induced T-cell lymphomagenesis.

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.

Identification of a novel alternatively spliced septin

Septins are a family of cytoskeletal proteins involved in cytokinesis, targeting of proteins to specific sites on the plasma membrane, and cellular morphogenesis. While many aspects of their function in cytokinesis in yeast cells have been investigated, the function of septins in mammalian cells is less well understood. For example, septins are present in post-mitotic neurons, suggesting they have other roles in, for example, establishing cell polarity. The full extent of the septin gene family is not known in mammalian cells. To better understand the septin gene family, we have cloned and characterized a novel mammalian septin.

Identification of Septins in Neurofibrillary Tangles in Alzheimer's Disease

Septins are evolutionarily conserved cytoskeletal GTPases that can form heteropolymer complexes involved in cytokinesis and other cellular processes. We detected expression of the human septin genes Nedd5, H5, Diff6, and hCDC100 in postmortem brain tissues using the reverse transcription-coupled polymerase chain reaction and their products by immunoblot analysis. Four antibodies directed against three septins, Nedd5, H5, and Diff6, consistently labeled neurofibrillary tangles, neuropil threads, and dystrophic neurites in the senile plaques in brains affected by Alzheimer's disease but did not label obvious structures in young control brains. Immunoelectron microscopy revealed that Nedd5 localized to the paired helical filaments. Pre-tangles, the precursory granular deposits that accumulate in the neuronal cytoplasm, also were labeled with the antibodies. These findings suggest that at least the three septins are associated with tau-based paired helical filament core, and may contribute to the formation of neurofibrillary tangle as integral constituents of paired helical filaments.

Structure and expression of the human septin gene HCDCREL-1.

Septins are a family of highly conserved filament-forming proteins that have been shown to mediate cytokinesis and cytoskeletal organization in fungi and Drosophila. The gene encoding the human septin family member HCDCREL-1 has been shown to be transcribed from a locus immediately adjacent to that of the platelet glycoprotein (GP) Ib b. The HCDCREL-1 gene possesses a non-consensus polyadenylation signal that apparently is not efficiently utilized, resulting in the expression of a readthrough transcript also containing the platelet GPIb beta coding region. As a first step in understanding the regulation and function of HCDCREL-1, we have analyzed the structure of this gene and characterized its expression in a variety of human cells. Our results indicate that the gene is expressed at high levels in platelets and neural tissue, and is transcriptionally complex.

SPR28, a sixth member of the septin gene family in Saccharomyces cerevisiae that is expressed specifically in sporulating cells.

The septins are a recently recognized family of proteins that are present in a wide variety of fungal and animal cells, where they are involved in cytokinesis and apparently in other processes involving the organization of the cell surface. Five previously described Saccharomyces cerevisiae septins are associated with the neck filaments of vegetative cells and/or with the developing prospore wall of sporulating cells. We report here the characterization of SPR28, a sixth member of the S. cerevisiae septin gene family whose existence was revealed by the yeast genome project. Analysis of mRNA levels showed that SPR28 is a new member of the group of "late genes' that are expressed at high levels during the meiotic divisions and ascospore formation. The septin it encodes, Spr28p, exhibited specific two-hybrid interactions with itself and with three other septins that are expressed in sporulating cells. Consistent with these results, an Spr28p-green fluorescent protein fusion was induced during meiosis I and appeared to be associated with the developing prospore walls. Deletion of SPR28 in either a wild-type or an spr3 delta background produced no obvious abnormalities in vegetative cells and had little or no effect on sporulation, suggesting that the septins have redundant roles during spore formation.