Genetic Factors Affecting Sperm Chromatin Structure

Loss of histone reader Phf7 leads to immune pathways activation via endogenous retroviruses during spermiogenesis

Genetic studies have elucidated the critical roles of Phf7 in germline development in animals; however, the exact etiology of Phf7 mutations leading to male infertility and the possibility of mechanism-based therapy are still unclear and warrant further investigation. Using the Phf7 knockout mouse model, we verified that genetic defects were responsible for male infertility by preventing histone-to-protamine exchange, as previously reported. The deficiency of spermatogenesis caused by Phf7 deletion through the endogenous retrovirus-mediated activation of the immune pathway is a common mechanism of infertility. Furthermore, we identified PPARα as a promising target of immunity and inflammation in the testis, where endogenous retroviruses are suppressed, and Phf7 as a crucial regulator of endogenous retrovirus-mediated immune regulation and revealed its role as an epigenetic reader. The loss of Phf7 activates immune pathways, which can be rescued by the PPARα agonist astaxanthin. These results showed that astaxanthin is a potential therapeutic agent for treating male infertility. The findings in our study provide insights into the molecular mechanisms underlying male infertility and suggest potential targets for future research and therapeutic development.

Long-term sperm storage in eusocial Hymenoptera

In internally fertilizing species, sperm transfer is not always immediately followed by egg fertilization, and female sperm storage (FSS) may occur. FSS is a phenomenon in which females store sperm in a specialized organ for periods lasting from a few hours to several years, depending on the species. Eusocial hymenopterans (ants, social bees, and social wasps) hold the record for FSS duration. In these species, mating takes place during a single nuptial flight that occurs early in adult life for both sexes; they never mate again. Males die quickly after copulation but survive posthumously as sperm stored in their mates' spermathecae. Reproductive females, also known as queens, have a much longer life expectancy, up to 20 years in some species. Here, we review what is currently known about the molecular adaptations underlying the remarkable FSS capacities in eusocial hymenopterans. Because sperm quality is crucial to the reproductive success of both sexes, we also discuss the mechanisms involved in sperm storage and preservation in the male seminal vesicles prior to ejaculation. Finally, we propose future research directions that should broaden our understanding of this unique biological phenomenon.

Insights into the sperm chromatin and implications for male infertility from a protein perspective

Male germ cells undergo an extreme but fascinating process of chromatin remodeling that begins in the testis during the last phase of spermatogenesis and continues through epididymal sperm maturation. Most of the histones are replaced by small proteins named protamines, whose high basicity leads to a tight genomic compaction. This process is epigenetically regulated at many levels, not only by posttranslational modifications, but also by readers, writers, and erasers, in a context of a highly coordinated postmeiotic gene expression program. Protamines are key proteins for acquiring this highly specialized chromatin conformation, needed for sperm functionality. Interestingly, and contrary to what could be inferred from its very specific DNA-packaging function across protamine-containing species, human sperm chromatin contains a wide spectrum of protamine proteoforms, including truncated and posttranslationally modified proteoforms. The generation of protamine knock-out models revealed not only chromatin compaction defects, but also collateral sperm alterations contributing to infertile phenotypes, evidencing the importance of sperm chromatin protamination toward the generation of a new individual. The unique features of sperm chromatin have motivated its study, applying from conventional to the most ground-breaking techniques to disentangle its peculiarities and the cellular mechanisms governing its successful conferment, especially relevant from the protein point of view due to the important epigenetic role of sperm nuclear proteins. Gathering and contextualizing the most striking discoveries will provide a global understanding of the importance and complexity of achieving a proper chromatin compaction and exploring its implications on postfertilization events and beyond. This article is categorized under: Reproductive System Diseases > Genetics/Genomics/Epigenetics Reproductive System Diseases > Molecular and Cellular Physiology.

Association of Single Nucleotide Polymorphisms in the PYGO2 and PRDM9 Genes with Idiopathic Azoospermia in Iranian Infertile Male Patients

Background

Azoospermia is a risk factor for infertility affecting approximately 1% of the male population. Genetic factors are associated with non-obstructive azoospermia (NOA). Pygo2 and PRDM9 genes are involved in the spermatogenesis process. The present study aimed to assess the association of single nucleotide polymorphism (SNP) in the Pygo2 (rs61758740 and rs61758741) and PRDM9 (rs2973631 and rs1874165) genes with idiopathic azoospermia (IA).

Methods

A cross-sectional study was conducted from October 2018 to August 2019 at Rooya Infertility Centre (Qom, Iran). A total of 100 infertile patients with NOA and 100 men with normal fertility were enrolled in the study. Tetra-primer amplification refractory mutation system-PCR method was used to detect SNPs rs61758740, rs61758741, and rs2973631. The restriction fragment length polymorphism method was used for SNP rs1874165. In addition, luteinizing, follicle-stimulating, and testosterone hormone levels were measured.

Results

The results showed a significant increase in luteinizing and follicle-stimulating hormone levels in the patient group (P<0.001), but a non-significant difference in testosterone levels in both groups. SNP rs61758740 (T>C) was associated with the increased risk of azoospermia (OR: 2.359, 95% Cl: 1.192-4.666, P=0.012). SNP rs2973631 showed a significant difference in genotype frequency between the patient and control groups in the dominant, recessive, and codominant models. However, in the case of SNP rs1874165, the difference was significant in the dominant, codominant, and overdominant models.

Conclusion

There is an association between azoospermia and SNPs in Pygo2 and PRDM9 genes in Iranian infertile male patients with IA. SNPs can be considered a risk factor for male infertility. It should be noted that this article was published in preprint form on the website of europepmc (https://europepmc.org/article/ppr/ppr416800).

Human Sperm Morphology as a Marker of Its Nuclear Quality and Epigenetic Pattern

Background: Human sperm chromatin condensation is a sum of epigenetic events that allows for the near-complete replacement of histones with protamines. Under high-magnification microscopy, nuclear vacuoles have been described as thumbprints with poor chromatin condensation. The objective of this study is to examine whether vacuolated spermatozoa carry specific epigenetic marks, which may influence embryo development. Methods: The presence and three-dimensional distribution of ten epigenetic marks (protamine-P2, histone-H3, H3K4me1/me2/me3, H3K9me1/me2/me3, H3K27me3, H4k20me2) were evaluated and compared in morphometrically normal spermatozoa according to the presence or absence of a large vacuole occupying more than 15% of the head surface (n = 4193). Results: Vacuolated spermatozoa were significantly more frequently labelled with H3 and H3K4me3 than normal spermatozoa (88.1% ± 2.7 and 78.5% ± 5.2 vs. 74.8% ± 4.8 and 49.1% ± 7.4, respectively; p = 0.009 and p < 0.001) and significantly less marked by P2 and H3K27me3 (50.2% ± 6.2 and 63.9% ± 6.3 vs. 82.1% ± 4.4 and 73.6% ± 5.1, respectively; p < 0.001 and p = 0.028). In three dimensions, vacuoles are nuclear concavities filled with DNA carrying the H3K4me3 marker. Conclusion: High-magnification microscopy is a simple tool to estimate in real time the sperm epigenetic profile. The selection of normal spermatozoa without vacuoles and the deselection of spermatozoa with vacuoles appear to be epigenetically favorable to embryo development and safe offspring.

Cyclin-dependent kinase 7 is essential for spermatogenesis by regulating retinoic acid signaling pathways and the STAT3 molecular pathway

Spermatogenesis is a complex process that requires precise regulation. Phosphorylation plays a role in spermatogenesis by regulating protein structure and activity. This study focused on cyclin-dependent kinase 7 (CDK7), and explored its function and molecular mechanisms in spermatogenesis in vitro in a cell line and in vivo in a mouse model. Inhibition of CDK7 activity affected spermatogonia proliferation and differentiation, and we found that CDK7 regulates retinoic acid (RA)-mediated c-KIT expression to play a role in spermatogonia. Then, we demonstrated that inhibition of CDK7 affected meiosis initiation, DNA repair, and synaptonemal complex formation in meiosis progression, and CDK7 played this role by regulating RA-mediated STRA8 and REC8 signaling pathways. Moreover, inhibition of CDK7 impacted spermatid differentiation and resulted in decreased counts, decreased motility, and increased head deformity of sperm. We demonstrated that CDK7 affects germ cell apoptosis and sperm motility by activating STAT3 and that STAT3 further regulates Cortactin expression to influence the nuclear elongation, chromatin condensation, and acrosome formation of sperm. Additionally, EP300 was identified as another potential target phosphorylated by CDK7 that participates in chromatin condensation. Our results demonstrated the important role of CDK7 in all key aspects of spermatogenesis, potentially providing an effective target for clinical diagnosis and pathogenesis.

Could high DNA stainability (HDS) be a valuable indicator of sperm nuclear integrity?

Background

The Sperm Chromatin Structure Assay (SCSA®), in addition to identifying the DNA Fragmentation Index (DFI) also identifies High DNA satiability (HDS), supposed to reflect the nuclear compaction of spermatozoa. However, data on what exactly this parameter reveals, its relevance and usefulness are contradictory. In order to shed light on this situation, spermatozoa of a cohort (N = 397) of infertile men were subjected to the SCSA®, TUNEL (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling) and CMA3 (Chromomycin A3) tests. In a smaller subcohort (N = 100), aniline blue (AB) and toluidine blue (TB) staining were performed in addition. The objective of this study was thus to answer the question of whether HDS is a relevant and reliable parameter to be taken into account?

Results

HDS does not appear to be a reliable indicator of nuclear immaturity because it shows a weak correlation with the CMA3, AB and TB stains. The low correlation of HDS with sperm DNA fragmentation (TUNEL and SCSA®) and DNA condensation (CMA3, AB and TB) tests suggests that these two parameters could be decoupled. Unlike DFI and TUNEL, HDS has not been shown to correlate with classic clinical situations of male infertility (asthenozoospermia, teratozoospermia or astheno-teratozoospermia).

Conclusion

HDS correlates poorly with most tests that focus specifically on the level of maturity of the sperm nucleus. To our knowledge, this study is the first to compare SCSA®, TUNEL, AB, TB and CMA3 assays on identical samples. It shows the potency, consistency and limitations of each test and the care that must be taken in their interpretation.