Research question
Dysfunction of septins, the fourth cytoskeleton protein, leads to male infertility because of sperm morphological abnormalities. SEPT14 is highly enriched in testis, but there are no reports about the role of SEPT14 in infertility. Here we aimed to clarify whether and how SEPT14 cause sperm defects.
Design
254 infertile patients and 116 controls were recruited. After extraction of genomic DNA from sperm, we used polymerase chain reaction-based direct sequencing to detect genetic variants in the entire coding region of SEPT14. The DNA damage and ultrastructure of sperm was evaluated. We also identified the binding partner of SEPT14 and evaluated how SEPT14 mutations affect the binding partner in the sperm.
Results
Two heterozygous mutations, p.Ala123Thr and p.Ile333Thr, were identified in the patients with teratozoospermia, but not in controls. Both positions were highly evolutionarily conserved among vertebrates. Results from fine morphological and chromatin structural analysis indicated severely malformed sperm heads with abnormal chromatin packaging. Compared with controls, prominent apoptosis and high DNA fragmentation was revealed in the sperm from the patients carrying SEPT14 mutations. ACTN4, a cytoskeleton actin-binding protein and participates in the organization of actin framework, interacts with SEPT14 in germ cell line. Furthermore, the localization of ACTN4 was disturbed in the sperm from patients carrying SEPT14 mutations.
Conclusions
The identification of two missense mutations with potentially deteriorating effects on sperm head morphology and DNA damage provides strong evidence to support the notion that SEPT14 is critical for male fertility. SEPT14 probably mediates the coupling of ACTN4 to actin and further affects the actin organization during head shaping.