SEPT12 interacts with SEPT6 and this interaction alters the filament structure of SEPT6 in Hela cells

SEPTIN12 c.474 G > A polymorphism as a risk factor in teratozoospermic patients

Teratozoospermia is a condition related to poor morphologically normal sperm count below the lower reference limit, which could hinder natural conception. Single nucleotide polymorphisms (SNPs) in the genes involved in sperm production and testicular function are proved to be risk factors, resulting in decreased sperm parameters and defects in sperm morphology. c.474 G > A polymorphism in the SEPTIN12 gene which is one of the testis-specific genes creates a novel splice variant and the resulting truncated protein was previously found to be more prevalent in infertile men. We aimed to investigate the association of SEPTIN12 c.474 G > A polymorphism with male infertility in teratozoospermia patients. Forty-eight teratozoospermic patients, diagnosed according to Kruger's criteria and 164 fertile controls who fathered at least 1 child within 3 years without assisted reproductive technologies were included into our prospective randomized controlled study. PCR-RFLP method was used for genotyping. Although no statistical difference was found between teratozoospermic patients and fertile controls in terms of genotype distributions, significance was identified between the genotypes of all and non-smoking teratozoopermic patients in terms of neck defects. SEPTIN12 c.474 G > A polymorphism was shown to be associated with sperm neck defects in teratozoospermic patients using the dominant statistical model. Smoking was identified as a risk factor for the sperm morphology defects in teratozoospermic A allele carriers.

CDC42 Negatively Regulates Testis-Specific SEPT12 Polymerization

Septin (SEPT) genes encode well-preserved polymerizing GTP-binding cytoskeletal proteins. The cellular functions of SEPTs consist of mitosis, cytoskeletal remodeling, cell polarity, and vesicle trafficking through interactions with various types of cytoskeletons. We discovered that mutated SEPTIN12 in different codons resulted in teratozoospermia or oligozoospermia. In mouse models with a defective Septin12 allele, sperm morphology was abnormal, sperm count decreased, and sperms were immotile. However, the regulators of SEPT12 are completely unknown. Some studies have indicated that CDC42 negatively regulates the polymerization of SEPT2/6/7 complexes in mammalian cell lines. In this study, we investigated whether CDC42 modulates SEPT12 polymerization and is involved in the terminal differentiation of male germ cells. First, through scanning electron microscopy analysis, we determined that the loss of Septin12 caused defective sperm heads. This indicated that Septin12 is critical for the formation of sperm heads. Second, CDC42 and SEPT12 were similarly localized in the perinuclear regions of the manchette at the head of elongating spermatids, neck region of elongated spermatids, and midpiece of mature spermatozoa. Third, wild-type CDC42 and CDC42Q61L (a constitutive-acting-mutant) substantially repressed SEPT12 polymerization, but CDC42T17N (a dominant-negative-acting mutant) did not, as evident through ectopic expression analysis. We concluded that CDC42 negatively regulates SEPT12 polymerization and is involved in terminal structure formation of sperm heads.

Interaction of Recombinant Gallus gallus SEPT5 and Brain Proteins of H5N1-Avian Influenza Virus-Infected Chickens

Septin forms a conserved family of cytoskeletal guanosine triphosphate (GTP) binding proteins that have diverse roles in protein scaffolding, vesicle trafficking, and cytokinesis. The involvement of septins in infectious viral disease pathogenesis has been demonstrated by the upregulation of SEPT5 protein and its mRNA in brain tissues of H5N1-infected chickens, thus, providing evidence for the potential importance of this protein in the pathogenesis of neurovirulence caused by the avian influenza virus. In this study, cloning, expression, and purification of Gallus gallus SEPT5 protein was performed in Escherichia coli. The SEPT5 gene was inserted into the pRSETB expression vector, transformed in the E. coli BL21 (DE3) strain and the expression of SEPT5 protein was induced by IPTG. The SEPT5 protein was shown to be authentic as it was able to be pulled down by a commercial anti-SEPT5 antibody in a co-immunoprecipitation assay. In vivo aggregation of the recombinant protein was limited by cultivation at a reduced temperature of 16 °C. Using co-immunoprecipitation techniques, the purified recombinant SEPT5 protein was used to pull down host’s interacting or binding proteins, i.e., proteins of brains of chickens infected with the H5N1 influenza virus. Interacting proteins, such as CRMP2, tubulin proteins, heat-shock proteins and other classes of septins were identified using LCMS/MS. Results from this study suggest that the codon-optimized SEPT5 gene can be efficiently expressed in the E. coli bacterial system producing authentic SEPT5 protein, thus, enabling multiple host’s proteins to interact with the SEPT5 protein.

SEPT12 orchestrates the formation of mammalian sperm annulus by organizing core octameric complexes with other SEPT proteins

Male infertility has become a worldwide health problem, but the etiologies of most cases are still unknown. SEPT12, a GTP-binding protein, is involved in male fertility. Two SEPT12 mutations (SEPT12(T89M) and SEPT12(D197N)) have been identified in infertile men who have a defective sperm annulus with a bent tail. The function of SEPT12 in the sperm annulus is still unclear. Here, we found that SEPT12 formed a filamentous structure with SEPT7, SEPT 6, SEPT2 and SEPT4 at the sperm annulus. The SEPT12-based septin core complex was assembled as octameric filaments comprising the SEPT proteins 12-7-6-2-2-6-7-12 or 12-7-6-4-4-6-7-12. In addition, the GTP-binding domain of SEPT12 was crucial for its interaction with SEPT7, and the N- and C-termini of SEPT12 were required for the interaction of SEPT12 with itself to polymerize octamers into filaments. Mutant mice carrying the SEPT12(D197N) mutation, which disrupts SEPT12 filament formation, showed a disorganized sperm annulus, bent tail, reduced motility and loss of the SEPT ring structure at the sperm annulus. These phenotypes were also observed in an infertile man carrying SEPT12(D197N). Taken together, our results demonstrate the molecular architecture of SEPT12 filaments at the sperm annulus, their mechanical support of sperm motility, and their correlation with male infertility.

SEPTIN12 genetic variants confer susceptibility to teratozoospermia

It is estimated that 10-15% of couples are infertile and male factors account for about half of these cases. With the advent of intracytoplasmic sperm injection (ICSI), many infertile men have been able to father offspring. However, teratozoospermia still remains a big challenge to tackle. Septins belong to a family of cytoskeletal proteins with GTPase activity and are involved in various biological processes e.g. morphogenesis, compartmentalization, apoptosis and cytokinesis. SEPTIN12, identified by c-DNA microarray analysis of infertile men, is exclusively expressed in the post meiotic male germ cells. Septin12(+/+)/Septin12(+/-) chimeric mice have multiple reproductive defects including the presence of immature sperm in the semen, and sperm with bent neck (defect of the annulus) and nuclear DNA damage. These facts make SEPTIN12 a potential sterile gene in humans. In this study, we sequenced the entire coding region of SEPTIN12 in infertile men (n = 160) and fertile controls (n = 200) and identified ten variants. Among them is the c.474 G>A variant within exon 5 that encodes part of the GTP binding domain. The variant creates a novel splice donor site that causes skipping of a portion of exon 5, resulting in a truncated protein lacking the C-terminal half of SEPTIN12. Most individuals homozygous for the c.474 A allele had teratozoospermia (abnormal sperm <14%) and their sperm showed bent tail and de-condensed nucleus with significant DNA damage. Ex vivo experiment showed truncated SEPT12 inhibits filament formation in a dose-dependent manner. This study provides the first causal link between SEPTIN12 genetic variant and male infertility with distinctive sperm pathology. Our finding also suggests vital roles of SEPT12 in sperm nuclear integrity and tail development.

SEPT12 mutations cause male infertility with defective sperm annulus

Septins are members of the GTPase superfamily, which has been implicated in diverse cellular functions including cytokinesis and morphogenesis. Septin 12 (SEPT12) is a testis-specific gene critical for the terminal differentiation of male germ cells. We report the identification of two missense SEPT12 mutations, c.266C>T/p.Thr89Met and c.589G>A/p.Asp197Asn, in infertile men. Both mutations are located inside the GTPase domain and may alter the protein structure as suggested by in silico modeling. The p.Thr89Met mutation significantly reduced guanosine-5'-triphosphate (GTP) hydrolytic activity, and the p.Asp197Asn mutation (SEPT12(D197N)) interfered with GTP binding. Both mutant SEPT12 proteins restricted the filament formation of the wild-type SEPT12 in a dose-dependent manner. The patient carrying SEPT12(D197N) presented with oligoasthenozoospermia, whereas the SEPT12(T89M) patient had asthenoteratozoospermia. The characteristic sperm pathology of the SEPT12(D197N) patient included defective annulus with bent tail and loss of SEPT12 from the annulus of abnormal sperm. Our finding suggests loss-of-function mutations in SEPT12 disrupted sperm structural integrity by perturbing septin filament formation.

Single nucleotide polymorphisms in the SEPTIN12 gene may be associated with azoospermia by meiotic arrest in Japanese men

PURPOSE

To investigate the association between SEPTIN12 gene variants and the risk of azoospermia caused by meiotic arrest.

METHODS

Mutational analysis of the SEPTIN12 gene was performed using DNA from 30 Japanese patients with azoospermia by meiotic arrest and 140 fertile male controls.

RESULTS

The frequencies of the c.204G>C (Gln38His) allele and the CC genotype were significantly higher in patients than in fertile controls (p < 0.05).

CONCLUSION

The c.204G>C (Gln38His) variant in the SEPTIN12 gene was associated with increased susceptibility to azoospermia caused by meiotic arrest.

The role of the septin family in spermiogenesis

SEPTINS (FULL NAME: Septin; symbol name: SEPT) belong to a family of polymerizing GTP-binding proteins that are required for many cellular functions, including membrane compartmentalization, vesicle trafficking, mitosis and cytoskeletal remodeling. Two of the 14 family members in the mammalian species, Septin12 and 14 are expressed specifically in the testis. In the mouse, knockout of Septin4 and Septin12 leads to male sterility with distinctive sperm pathology (defective annulus or bent neck). In humans, sperm with abnormal expression patterns of SEPT4, 7 and 12 are more prevalent in infertile men. How septin filament is assembled/dissembled and how the SEPT-related complex regulates spermatogenesis still await further investigation.

Conquering the complex world of human septins: implications for health and disease

Septins are highly conserved filamentous proteins first characterized in budding yeast and subsequently identified in must eukaryotes. Septins can bind and hydrolyze GTP, which is intrinsically related to their formation of septin hexamers and functional protein interactions. The human septin family is composed of 14 loci, SEPT1-SEPT14, which encode dozens of different septin proteins. Their central GTPase and polybasic domain regions are highly conserved but they diverge in their N-terminus and/or C-terminus. The mechanism by which the different isoforms are generated is not yet well understood, but one can hypothesize that the use of different promoters and/or alternative splicing could give rise to these variants. Septins perform diverse cellular functions according to tissue expression and their interacting partners. Functions identified to date include cell division, chromosome segregation, protein scaffolding, cellular polarity, motility, membrane dynamics, vesicle trafficking, exocytosis, apoptosis, and DNA damage response. Their expression is tightly regulated to maintain proper filament assembly and normal cellular functions. Alterations of these proteins, by mutation or expression changes, have been associated with a variety of cancers and neurological diseases. The association of septins with cancer results from alterations of expression in solid tumors or translocations in leukemias [mixed lineage leukemia (MLL)]. Expression changes in septins have also been associated with neurological conditions such as Alzheimer's and Parkinson's disease, as well as retinopathies, hepatitis C, spermatogenesis and Listeria infection. Pathogenic mutations of SEPT9 were identified in the autosomal dominant neurological disorder hereditary neuralgic amyotrophy (HNA). Human septin research over the past decade has established their importance in cell biology and human disease. Further functional characterization of septins is crucial to our understanding of their possible diagnostic, prognostic, and therapeutic applications.