The role of spermatozoa-zona pellucida interaction in selecting fertilization-competent spermatozoa in humans

Genetic variation in zona pellucida-3 (ZP3) gene and its association with litter size variation in Kari sheep

Variation in litter size (LS) in sheep is linked to genetic factors, including the Zona pellucida-3 (ZP3) gene, which plays a role in ovine reproductive processes. This study examined the association between ZP3 gene variations and LS in Kari sheep. Two groups of 160 Kari ewes were analysed: one consistently producing singletons and another producing twins, with occasional triplets. Additionally, Madakhlasht sheep, which sometimes produce twins, and Balkhi sheep, which produce only singletons, were used as references. The entire ZP3 gene was amplified using PCR and sequenced at 30× with Next Generation Sequencing. Bioinformatics analysis identified 70 variants across the three breeds, located in upstream regions, introns, and exons. Notably, two point mutations and a six-nucleotide insertion were found upstream of the initiation codon in twin-producing Kari ewes, potentially affecting ZP3 expression and LS. Two missense mutations (I101L in exon 1 and R408H in exon 8) were heterozygous in twin-producing Kari ewes but homozygous in other groups, correlating with LS. Protein modelling suggested that the I101L mutation alters the binding site, potentially impacting protein function. These findings indicate that ZP3 gene variations influence reproductive efficiency and LS in sheep, with specific variants serving as potential markers for selective breeding to enhance LS.

Assisted sperm fusion insemination improves fertilization rates and increases usable embryos for transfer: a clinical sibling-oocyte study

Objective

To evaluate the impact of assisted sperm fusion insemination (ASFI), a microinsemination method using sperm bound to the zona pellucida (ZP-sperm) without penetrating the oocyte membrane, compared with conventional intracytoplasmic sperm injection (C-ICSI), on fertilization and embryonic development.

Design

Prospective clinical sibling-oocyte study.

Subjects

A total of 197 oocytes from 24 patients who underwent 35 oocyte retrieval cycles from January 2023 to April 2024 were analyzed. Patients who underwent retrieval of both, at least 2 metaphase II (MII) oocytes and at least 1 immature or degenerated oocyte, were recruited.

Intervention

Metaphase II oocytes were alternately allocated to 2 groups: ASFI and C-ICSI groups. To obtain ZP-sperm for ASFI, immature or degenerated oocytes were incubated with 10,000 motile sperm for 3 hours. After harvesting the ZP-sperm, it was pressed onto the membrane of an MII oocyte for 10 seconds in the ASFI group. Conventional intracytoplasmic sperm injection was performed conventionally in the C-ICSI group.

Main Outcome Measures

The rates of 2 pronuclei (2PN), degeneration, blastocyst formation, and usable embryos, defined as the total number of transferred or cryopreserved embryos divided by the number of MII oocytes, were compared between the 2 groups.

Results

The 2PN rate of the ASFI group was 88.0% (73/83), which was significantly higher than that of the C-ICSI group (70.2% [80/114]). In addition, a significantly lower degeneration rate was observed in the ASFI group (0% [0/83]) than in the C-ICSI group (8.8% [10/114]). The blastocyst formation rate was equivalent in the 2 groups (ASFI group, 63.9% [39/61]; C-ICSI group, 62.0% [44/71]). However, the usable embryo rate was significantly higher in the ASFI group (45.8% [38/83]) than in the C-ICSI group (28.1% [32/114]).

Conclusion

The ASFI group yielded significantly higher 2PN and lower degeneration rates than the C-ICSI group. Consequently, the ASFI group experienced a higher number of embryos usable for implantation, although there was no significant difference in the blastocyst formation rate between the 2 groups. Further studies with a larger number of cases will be needed for more general application of these findings.

Evolutionary Aspects of Sperm Physiology and Its Assessment

Diversity in sperm morphology and performance could be explained by differences in molecular and cellular mechanisms that underlie the processes of sperm formation in the testis and maturation in the epididymis. Furthermore, there are additional differences in mechanisms that prepare the sperm for fertilization, once they are transferred to the female tract. Another level of understanding of sperm diversity requires the analysis of selective forces mainly related to post-copulatory sexual selection. Sperm competition and cryptic female choice have been identified as important agents driving the evolution of sperm morphology and function. Learning about mechanisms and selective forces is crucial for the design of tests to assess sperm quality, either in a clinical context or to probe their fertilizing capacity in assisted reproduction or reproductive biotechnologies. In addition, this will be important to understand the impact on fertility of new pharmaceuticals or environmental factors.

A narrative review of sperm selection technology for assisted reproduction techniques

Background and Objective

In-vitro fertilization (IVF) with intracytoplasmic sperm injection (ICSI) has become increasingly prevalent even in cases without significant male factor infertility; however, stagnant live-birth rates, both nationally and internationally, have driven more research into sperm selection. To date, nothing has replaced swim-up and density-gradient preparation methods and therefore we sought to review the state of the science.

Methods

A PubMed search was performed between years of 1989 and 2024 for English research articles reporting data on sperm selection technology in assisted reproductive technology.

Key Content and Findings

IVF with ICSI is increasingly prevalent even in men with normal semen parameters. Despite technologic advances and widespread use, reproductive outcomes with ICSI have been stagnant. This market for opportunity growth has allowed for sperm selection techniques to grow exponentially with heterogeneity in utilization and a paucity of positive reproductive outcomes. Swim-up and density-gradient centrifugation remain the most utilized sperm selection techniques. Various future technologies show promise including epigenetics, sperm biomarkers and a potential role of artificial intelligence; however, more research is needed.

Conclusions

Given unchanged IVF success rates, sperm selection technologies hold promise to improve reproductive outcomes beyond traditional ICSI. At present, no technique has shown superiority to swim up and density centrifugation.

Genetic Diversity and Selection Signal Analysis of Hu Sheep Based on SNP50K BeadChip

This research is designed to examine the genetic diversity and kinship among Hu sheep, as well as to discover genes associated with crucial economic traits. A selection of 50 unrelated adult male Hu sheep underwent genotyping with the SNP50K BeadChip. Seven indicators of genetic diversity were assessed based on high-quality SNP data: effective population size (Ne), polymorphic information content (PIC), polymorphic marker ratio (PN), expected heterozygosity (He), observed heterozygosity (Ho), effective number of alleles, and minor allele frequency (MAF). Plink software was employed to compute the IBS genetic distance matrix and detect runs of homozygosity (ROHs), while the G matrix and principal component analysis were performed using GCTA software. Selective sweep analysis was carried out using ROH, Pi, and Tajima's D methodologies. This study identified a total of 64,734 SNPs, of which 56,522 SNPs remained for downstream analysis after quality control. The population displayed relatively high genetic diversity. The 50 Hu sheep were ultimately grouped into 12 distinct families, with families 6, 8, and 10 having the highest numbers of individuals, each consisting of 6 sheep. Furthermore, a total of 294 ROHs were detected, with the majority having lengths between 1 and 5 Mb, and the inbreeding coefficient FROH was 0.01. In addition, 41, 440, and 994 candidate genes were identified by ROH, Pi, and Tajima's D methods, respectively, with 3 genes overlapping (BMPR1B, KCNIP4, and FAM13A). These results offer valuable insights for future Hu sheep breeding, genetic assessment, and population management.

Sperm selection by zona adhesion improves assisted reproductive treatment outcomes

BACKGROUND

Zona pellucida is one of the main selective barriers for the spermatozoa before reaching the oocyte. Using native zona in the sperm selection prior to Intracytoplasmic Sperm Injection (ICSI) has been proven effective but inconvenient approach in In Vitro Fertilisation (IVF) laboratory. The application of autologous solubilised zonae pellucidae in the sperm selection prior to ICSI has not been studied yet.

OBJECTIVES

To compare the assisted reproductive treatment (ART) outcomes (implantation, pregnancy, live birth, and miscarriage rates) after ICSI performed with spermatozoa selected on their ability to adhere to immobilised solubilised zonae pellucidae and conventionally selected spermatozoa.

MATERIALS AND METHODS

In total, 500 couples fulfilled the inclusion criteria and 368 of them were included in the study. After random allocation, 192 couples had spermatozoa selected by sperm-zona adhesion for ICSI (study group) and 176 patients underwent standard ICSI (control group). In the study group, patients' own zonae were acid solubilised and immobilised on petri dishes. The partner's motile spermatozoa were placed in the dishes and the adhered spermatozoa were used for ICSI. For the control group, the conventional sperm selection by morphological criteria was applied prior ICSI. All women underwent frozen ET with euploid embryos. Chi square test was used to compare the data.

RESULTS

The sperm selection by zona adhesion resulted in significantly higher implantation rate (50.4% vs. 37.0%, p = 0.003), clinical pregnancy rate (43.8% vs. 33.3%, p = 0.018) and live birth rate (38.0% vs. 25.9%, p = 0.004) and significantly lower incidence of miscarriage (11.3% vs. 22.2%, p = 0.044) in comparison to the conventional method of the sperm selection.

DISCUSSION AND CONCLUSION

The application of solubilised zonae pellucidae in the sperm selection for ICSI benefits ART outcomes in couples with unexplained infertility. Moreover, sperm-zona selection significantly reduces the risk of miscarriages.

Differential Sperm Proteomics Reveals the Significance of Fatty Acid Synthase and Clusterin in Idiopathic Recurrent Pregnancy Loss

Recurrent pregnancy loss (RPL) is a pervasive health issue affecting a large number of couples globally, which leads to increased emotional and financial strain on the affected families. While female factors have been extensively studied and are well known, the contribution of male factors to RPL remains largely unknown. As high as 40% of RPL cases are unexplained, which are termed as idiopathic RPL (iRPL), necessitating the investigation of male factors. The role of spermatozoa in early embryonic development is now well established, and recent research studies have shown that oxidative stress and DNA fragmentation in sperm cells are linked to RPL. The aim of this study was to identify proteomic markers of iRPL in human spermatozoa using tandem mass spectrometry. A label-free method quantified a total of 1820 proteins, and statistical analysis identified 359 differentially expressed proteins, the majority of which were downregulated in iRPL samples (344). Bioinformatics analysis revealed that proteomic alterations were mainly associated with biological processes such as response to stress, protein folding, chromatin organization, DNA conformation change, oxidative phosphorylation, and electron transport chain. In coherence with past studies, we determined fatty acid synthase (FASN) and clusterin (CLU) to be the most potential sperm markers for iRPL and confirmed their expression changes in iRPL by western blotting. Conclusively, we believe that FASN and CLU might serve as potential markers of iRPL and suggest exploratory functional studies to identify their specific role in pregnancy loss.