Homozygous deleterious variants in the C-terminal of TDRD5 impair spermiogenesis, causing severe oligoasthenoteratozoospermia in humans.

BACKGROUND: PiRNA pathway factors, including evolutionarily conserved Tudor domain-containing proteins, play crucial roles in suppressing transposons and regulating post-meiotic gene expression. TDRD5 is essential for retrotransposon silencing and pachytene piRNA biogenesis; however, a causal link between TDRD5 variants and human infertility has not yet been established. OBJECTIVE: To identify the likely pathogenic variants of TDRD5 in infertile men, characterised by azoospermia or severe oligozoospermia. MATERIAL AND METHODS: Potential candidate variants were identified and confirmed using whole-exome and Sanger sequencing. Haematoxylin and eosin staining, immunofluorescence, and ultrastructural analyses were performed to investigate the structural and functional abnormalities of spermatozoa. The pathogenicity of the identified TDRD5 variants was verified using in vitro experiments. Functional effects of the C-terminal nonsense variant were assessed via histology, immunofluorescence staining, and small-RNA sequencing. Intracytoplasmic sperm injection (ICSI) was also performed to evaluate the efficacy of the clinical treatment. RESULTS: We identified a homozygous missense variant (c.3043G > A, p.A1015T) and a homozygous nonsense variant (c.2293G > T, p.E765*) of TDRD5 in two unrelated infertile men. Both patients exhibited severe oligoasthenoteratozoospermia, characterised by the presence of spermatozoa with multiple heads and/or flagella, as well as acrosomal hypoplasia. In vitro experiments revealed that the p.A1015T variant caused a diffuse distribution of TDRD5 granules, whereas the p.E765* variant led to the production of a C-terminal truncated protein with nuclear localisation, instead of the typical cytoplasmic localisation observed for the wild-type protein. Functional investigations also revealed that truncation of the C-terminal region of TDRD5 could potentially lead to a decline in the expression levels of intermitochondrial cement and chromatoid body components, such as MIWI (PIWIL1) and UPF1, and a slight decrease in the abundance of pachytene piRNA, ultimately resulting in compromised spermiogenesis. ICSI may be an effective treatment for these deficiencies. DISCUSSION AND CONCLUSION: This study implicates TDRD5 as a novel candidate gene in the pathogenesis of human male infertility, emphasising the contribution of piRNA pathway genes to male infertility. In addition, our data suggest that ICSI could be a promising treatment for infertile men harbouring TDRD5 variants.

Bi-allelic variants in chromatoid body protein TDRD6 cause spermiogenesis defects and severe oligoasthenoteratozoospermia in humans.

BACKGROUND: The association between the TDRD6 variants and human infertility remains unclear, as only one homozygous missense variant of TDRD6 was found to be associated with oligoasthenoteratozoospermia (OAT). METHODS: Whole-exome sequencing and Sanger sequencing were employed to identify potential pathogenic variants of TDRD6 in infertile men. Histology, immunofluorescence, immunoblotting and ultrastructural analyses were conducted to clarify the structural and functional abnormalities of sperm in mutated patients. Tdrd6-knockout mice were generated using the CRISPR-Cas9 system. Total RNA-seq and single-cell RNA-seq (scRNA-seq) analyses were used to elucidate the underlying molecular mechanisms, followed by validation through quantitative RT-PCR and immunostaining. Intracytoplasmic sperm injection (ICSI) was also used to assess the efficacy of clinical treatment. RESULTS: Bi-allelic TDRD6 variants were identified in five unrelated Chinese individuals with OAT, including homozygous loss-of-function variants in two consanguineous families. Notably, besides reduced concentrations and impaired motility, a significant occurrence of acrosomal hypoplasia was detected in multiple spermatozoa among five patients. Using the Tdrd6-deficient mice, we further elucidate the pivotal role of TDRD6 in spermiogenesis and acrosome identified. In addition, the mislocalisation of crucial chromatoid body components DDX4 (MVH) and UPF1 was also observed in round spermatids from patients harbouring TDRD6 variants. ScRNA-seq analysis of germ cells from a patient with TDRD6 variants revealed that TDRD6 regulates mRNA metabolism processes involved in spermatid differentiation and cytoplasmic translation. CONCLUSION: Our findings strongly suggest that TDRD6 plays a conserved role in spermiogenesis and confirms the causal relationship between TDRD6 variants and human OAT. Additionally, this study highlights the unfavourable ICSI outcomes in individuals with bi-allelic TDRD6 variants, providing insights for potential clinical treatment strategies.

Novel MEIOB pathogenic variants including a homozygous non-canonical splicing variant, cause meiotic arrest and human non-obstructive azoospermia.

Non-obstructive azoospermia (NOA) is the most severe form of human male infertility, and the genetic causes of NOA with meiotic arrest remain largely unclear. In this study, we identified novel compound heterozygous MEIOB variants (c.814C > T: p.R272X and c.976G > A: p.A326T) and a previously undescribed homozygous non-canonical splicing variant of MEIOB (c.528 + 3A > C) in two NOA-affected individuals from two irrelevant Chinese families. MEIOB missense variant (p.A326T) significantly reduced protein abundance and nonsense variant (p.R272X) produced a truncated protein. Both of two variants impaired the MEIOB-SPATA22 interaction. The MEIOB non-canonical splicing variant resulted in whole Exon 6 skipping by minigene assay, which was predicted to produce a frameshift truncated protein (p.S111Rfs*32). Histological and immunostaining analysis indicated that both patients exhibited a similar phenotype as we previously reported in Meiob mutant mice, that is, absence of spermatids in seminiferous tubules and meiotic arrest. Our study identified three novel pathogenic variants of MEIOB in NOA patients, extending the mutation spectrum of the MEIOB and highlighting the contribution of meiotic recombination related genes in human fertility.