Novel exon mutation in SYCE1 gene is associated with non-obstructive azoospermia

Novel Mutations Reduce Expression of Meiotic Regulators SYCE1 and BOLL in Testis of Azoospermic Men from West Bengal, India

We investigated the polymorphisms/mutations in synaptonemal complex central element protein 1 (SYCE1) and CDC25A mRNA-binding protein (BOLL) to test whether they increase the risk of azoospermia among Bengali-speaking men from West Bengal, India. Sanger's dideoxy sequencing was used to genotype 140 azoospermic individuals who tested negative for Y chromosome microdeletion and 120 healthy controls. In both cases and controls, qRT-PCR was used to determine the expression summary of SYCE1 and BOLL. The perceived harmful consequences of identified mutations were inferred using in silico analysis. Suitable statistical approaches were used to conduct the association study. We found SYCE1 177insT (ON245141), 10650T > G (ON257012), 10093insT (ON257013), 10653insG (ON292504), rs10857748A > G, rs10857749G > A, and rs10857750T > A and BOLL 7708T > A (ON245141insT), rs72918816T > C, and rs700655C > T variants with the prevalence of azoospermia. Data from qRT-PCR and in silico studies projected that the variations would either disrupt the transcript's natural splice junctions or cause probable damage to the structure of the genes' proteins. SYCE1 gene variants [177insT (ON245141), 10650T > G (ON257012), 10093insT (ON257013), 10653insG (ON292504), rs10857748A > G, rs10857749G > A, rs10857750T > A] and BOLL gene variants [7708T > A (ON245141insT), rs72918816T > C, rs700655C > T] reduce the expression of respective gene in testicular tissue among azoospermic male as revealed from qRT-PCR result. These genetic variations could be utilized as screening tools for male infertility to determine the best course of treatment in routine ART practise.

A homozygous frameshift variant in SYCP2 caused meiotic arrest and non-obstructive azoospermia

Genetic causation for the majority of non-obstructive azoospermia (NOA) remains unclear. Mutations in synaptonemal complex (SC)-associated genes could cause meiotic arrest and NOA. Previous studies showed that heterozygous truncating variants in SYCP2 encoding a protein essential for SC formation, are associated with non-obstructive azoospermia and severe oligozoospermia. Herein, we showed a homozygous loss-of-function variant in SYCP2 (c.2689_2690insT) in an NOA-affected patient. And this variant was inherited from heterozygous parental carriers by natural reproduction. HE, IF, and meiotic chromosomal spread analyses demonstrated that spermatogenesis was arrested at the zygotene stage in the proband with NOA. Thus, this study revealed that SYCP2 associated with NOA segregates in an autosomal recessive inheritance pattern, rather than an autosomal dominant pattern. Furthermore, our study expanded the knowledge of variants in SYCP2 and provided new insight into understanding the genetic etiology of NOA.

Meiotic Chromosome Structure, the Synaptonemal Complex, and Infertility

In meiosis, homologous chromosome synapsis is mediated by a supramolecular protein structure, the synaptonemal complex (SC), that assembles between homologous chromosome axes. The mammalian SC comprises at least eight largely coiled-coil proteins that interact and self-assemble to generate a long, zipper-like structure that holds homologous chromosomes in close proximity and promotes the formation of genetic crossovers and accurate meiotic chromosome segregation. In recent years, numerous mutations in human SC genes have been associated with different types of male and female infertility. Here, we integrate structural information on the human SC with mouse and human genetics to describe the molecular mechanisms by which SC mutations can result in human infertility. We outline certain themes in which different SC proteins are susceptible to different types of disease mutation and how genetic variants with seemingly minor effects on SC proteins may act as dominant-negative mutations in which the heterozygous state is pathogenic.

Genetic variants underlying spermatogenic arrests in men with non-obstructive azoospermia

Spermatogenic arrest is a severe form of non-obstructive azoospermia (NOA), which occurs in 10-15% of infertile men. Interruption in spermatogenic progression at premeiotic, meiotic, or postmeiotic stage can lead to arrest in men with NOA. Recent studies have intensively focused on defining genetic variants underlying these spermatogenic arrests by making genome/exome sequencing. A number of variants were discovered in the genes involving in mitosis, meiosis, germline differentiation and other basic cellular events. Herein, defined variants in NOA cases with spermatogenic arrests and created knockout mouse models for the related genes are comprehensively reviewed. Also, importance of gene panel-based screening for NOA cases was discussed. Screening common variants in these infertile men with spermatogenic arrests may contribute to elucidating the molecular background and designing novel treatment strategies.

Novel copy number variations within SYCE1 caused meiotic arrest and non-obstructive azoospermia

Background

Non-obstructive azoospermia (NOA) is the most severe disease in male infertility, but the genetic causes for majority of NOA remain unknown.

Methods

Two Chinese NOA-affected patients were recruited to identify the genetic causal factor of infertility. Whole-exome sequencing (WES) was conducted in the two patients with NOA. Sanger sequencing and CNV array were used to ascertain the WES results. Hematoxylin and eosin (H&E) staining and immunofluorescence (IF) were carried out to evaluate the stage of spermatogenesis arrested in the affected cases.

Results

Novel heterozygous deletion (LOH) within SYCE1 (seq[GRCh37] del(10)(10q26.3)chr10:g.135111754_135427143del) and heterozygous loss of function (LoF) variant in SYCE1 (NM_001143763: c.689_690 del:p.F230fs) were identified in one NOA-affected patient. While homozygous deletion within SYCE1 (seq[GRCh37] del(10)(10q26.3)chr10:g.135340247_135379115del) was detected in the other patient with meiotic arrest. H&E and IF staining demonstrated that the spermatogenesis was arrested at pachytene stage in the two patients with NOA, suggesting these two novel CNVs within SYCE1 could lead to meiotic defect and NOA.

Conclusions

We identified that two novel CNVs within SYCE1 are associated with meiotic arrest and male infertility. Thus, our study expands the knowledge of variants in SYCE1 and provides a new insight to understand the genetic etiologies of NOA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01288-8.