A novel homozygous frameshift mutation in MNS1 associated with severe oligoasthenoteratozoospermia in humans

A hemizygous loss-of-function variant in BCORL1 is associated with male infertility and oligoasthenoteratozoospermia

Oligoasthenoteratozoospermia (OAT) is a common type of male infertility; however, its genetic causes remain largely unknown. Some of the genetic determinants of OAT are gene defects affecting spermatogenesis. BCORL1 (BCL6 corepressor like 1) is a transcriptional corepressor that exhibits the OAT phenotype in a knockout mouse model. A hemizygous missense variant of BCORL1 (c.2615T > G:p.Val872Gly) was reported in an infertile male patient with non-obstructive azoospermia (NOA). Nevertheless, the correlation between BCORL1 variants and OAT in humans remains unknown. In this study, we used whole-exome sequencing to identify a novel hemizygous nonsense variant of BCORL1 (c.1564G > T:p.Glu522*) in a male patient with OAT from a Han Chinese family. Functional analysis showed that the variant produced a truncated protein with altered cellular localization and a dysfunctional interaction with SKP1 (S-phase kinase-associated protein 1). Further population screening identified four BCORL1 missense variants in subjects with both OAT (1 of 325, 0.31%) and NOA (4 of 355, 1.13%), but no pathogenic BCORL1 variants among 362 fertile subjects. In conclusion, our findings indicate that BCORL1 is a potential candidate gene in the pathogenesis of OAT and NOA, expanded its disease spectrum and suggested that BCORL1 may play a role in spermatogenesis by interacting with SKP1.

TENT5D disruption causes oligoasthenoteratozoospermia and male infertility

BACKGROUND

Oligoasthenoteratozoospermia (OAT) is one of the most complex aggregators of male gametic problems. However, the genetic etiology of OAT is still largely unknown.

OBJECTIVES

To reveal the new genetic factors responsible for male infertility owning to OAT and reveal the outcomes of the affected patients from intracytoplasmic sperm injection (ICSI).

MATERIALS AND METHODS

Two infertile men with typical OAT were recruited in 2018 and retrospected a cohort that included 47 patients with OAT from 2013 to 2021. Fifty healthy men with proven fertility served as control subjects. To identify the novel pathogenic variants, whole-exome sequencing and Sanger sequencing were used. In silico analysis revealed the affecting of the variants. Field emission scanning electron microscopy was employed to observe the morphological defects of the spermatozoa. Immunofluorescence was used to analyze the expression and localization of the related protein. CRISPR/Cas9 was used to generate the mouse model. ICSI was used as a treatment for the patients and to assess the effects of the pathogenic variant on fertilization and embryo development.

RESULTS

We identified a loss-of-function mutation NM_001170574.2:c.823G > T (p.Glu275*) in X-linked TENT5D from two patients with OAT. This variant is highly deleterious and has not been found in the human population. The count of patients' spermatozoa is dramatically decreased and displays multiple morphologic abnormalities with poor motility. Tent5d knockout mice are infertile and exhibit parallel defects. ICSI could rescue the infertility of the Tent5d knockout male mice. Moreover, the proband was treated with ICSI and achieved a successful pregnancy outcome for the first time. Subsequent mutation screening identified no TENT5D mutations among 47 additional patients with OAT and 50 control subjects.

CONCLUSION

Mutation in TENT5D results in OAT and male infertility, and this terrible situation could be rescued by ICSI.

Structures of sperm flagellar doublet microtubules expand the genetic spectrum of male infertility

Sperm motility is crucial for successful fertilization. Highly decorated doublet microtubules (DMTs) form the sperm tail skeleton, which propels the movement of spermatozoa. Using cryo-electron microscopy (cryo-EM) and artificial intelligence (AI)-based modeling, we determined the structures of mouse and human sperm DMTs and built an atomic model of the 48-nm repeat of the mouse sperm DMT. Our analysis revealed 47 DMT-associated proteins, including 45 microtubule inner proteins (MIPs). We identified 10 sperm-specific MIPs, including seven classes of Tektin5 in the lumen of the A tubule and FAM166 family members that bind the intra-tubulin interfaces. Interestingly, the human sperm DMT lacks some MIPs compared with the mouse sperm DMT. We also discovered variants in 10 distinct MIPs associated with a subtype of asthenozoospermia characterized by impaired sperm motility without evident morphological abnormalities. Our study highlights the conservation and tissue/species specificity of DMTs and expands the genetic spectrum of male infertility.

BBOF1 is required for sperm motility and male fertility by stabilizing the flagellar axoneme in mice

The sperm flagellum is a specialized type of motile cilium composed of a typical "9 + 2" axonemal structure with peri-axonemal structures, such as outer dense fibers (ODFs). This flagellar arrangement is crucial for sperm movement and fertilization. However, the association of axonemal integrity with ODFs remains poorly understood. Here, we demonstrate that mouse BBOF1 could interact with both MNS1, an axonemal component, and ODF2, an ODF protein, and is required for sperm flagellar axoneme maintenance and male fertility. BBOF1 is expressed exclusively in male germ cells from the pachytene stage onwards and is detected in sperm axoneme fraction. Spermatozoa derived from Bbof1-knockout mice exhibit a normal morphology, however, reduced motility due to the absence of certain microtubule doublets, resulting in the failure to fertilize mature oocytes. Furthermore, BBOF1 is found to interact with ODF2 and MNS1 and is also required for their stability. Our findings in mice suggest that Bbof1 could also be essential for human sperm motility and male fertility, thus is a novel potential candidate gene for asthenozoospermia diagnosis.

De novo identification of mammalian ciliary motility proteins using cryo-EM

Dynein-decorated doublet microtubules (DMTs) are critical components of the oscillatory molecular machine of cilia, the axoneme, and have luminal surfaces patterned periodically by microtubule inner proteins (MIPs). Here we present an atomic model of the 48-nm repeat of a mammalian DMT, derived from a cryoelectron microscopy (cryo-EM) map of the complex isolated from bovine respiratory cilia. The structure uncovers principles of doublet microtubule organization and features specific to vertebrate cilia, including previously unknown MIPs, a luminal bundle of tektin filaments, and a pentameric dynein-docking complex. We identify a mechanism for bridging 48- to 24-nm periodicity across the microtubule wall and show that loss of the proteins involved causes defective ciliary motility and laterality abnormalities in zebrafish and mice. Our structure identifies candidate genes for diagnosis of ciliopathies and provides a framework to understand their functions in driving ciliary motility.