Benchmarks defining high-quality sperm in the common marmoset (Callithrix jacchus)

BACKGROUND

Common marmosets (Callithrix jacchus) are increasingly recognized as valuable nonhuman primates (NHPs) for biomedical research due to their small size and short reproductive cycle and lifespan relative to other NHP species. Maximizing the utility of captive research marmosets, including genetically manipulated animals, will require the use of assisted reproductive techniques (ART) including manipulation, storage, and sharing of marmoset sperm. Here, we identify characteristics of high-quality semen samples and validate a simple method for selecting high-quality sperm.

METHODS

Computer-assisted sperm analysis (CASA) was used to evaluate sperm quality in semen samples collected from 44 marmosets and assessed the use of the swim-up method for the selection of high-quality sperm was also tested in half the samples as a potential means to optimize in vitro fertilization or intrauterine insemination.

RESULTS

For each reference parameter, samples at or below the 5th percentile were categorized as abnormal sperm, while those above the 5th percentile were considered to be normal. Among normal samples, those at or above the 50th percentile were categorized as high-quality. High-quality semen samples exhibited the following characteristics: semen volume ≥ 30 µL; sperm count ≥ 107/ejaculate; total motility ≥ 35%; and normal morphology ≥ 5%. Sperm isolated by swim-up exhibited superior sperm progressive motility (19.7% ± 4.5 vs. 5.6% ± 2.1; P = 0.01) and normal morphology (13.1 ± 1.59 vs. 7.65 ± 1.1; P < 0.001) compared with unselected sperm.

CONCLUSION

This study defines robust, statistically supported reference values for evaluating marmoset semen samples to assist with the identification of optimal sperm donors and the selection of high-quality sperm samples for assisted reproduction. Ultimately, these reference values combined with a validated selection method will contribute to consistent standards for the international sharing of genetically diverse and/or gene-edited marmoset sperm for research and reproduction.

Histone acetylation regulated by histone deacetylases during spermatogenesis

BACKGROUND

Physical, chemical, and biological factors in the environment constantly influence in vivo and in vitro biological processes, including diverse histone modifications involved in cancer and metabolism. However, the intricate mechanisms of acetylation regulation remain poorly elucidated. In mammalian spermatogenesis, acetylation plays a crucial role in repairing double-strand DNA breaks, regulating gene transcription, and modulating various signaling pathways.

RESULTS

This review summarizes the histone acetylation sites in the mouse testis and provides a comprehensive overview of how histone acetylation is involved in different stages of spermatogenesis under the regulation by histone deacetylases. The regulatory functions of various class histone deacetylases during spermatogenesis and the crossroad between histone acetylation and other histone modifications are highlighted. It is imperative to understand the mechanisms of histone acetylation regulated by histone deacetylases in spermatogenesis, which facilitates to prevent and treat infertility-related diseases.

Transcriptome profiling of histone writers/erasers enzymes across spermatogenesis, mature sperm and pre-cleavage embryo: Implications in paternal epigenome transitions and inheritance mechanisms

Accumulating evidence points out that sperm carry epigenetic instructions to embryo in the form of retained histones marks and RNA cargo that can transmit metabolic and behavioral traits to offspring. However, the mechanisms behind epigenetic inheritance of paternal environment are still poorly understood. Here, we curated male germ cells RNA-seq data and analyzed the expression profile of all known histone lysine writers and erasers enzymes across spermatogenesis, unraveling the developmental windows at which they are upregulated, and the specific activity related to canonical and non-canonical histone marks deposition and removal. We also characterized the epigenetic enzymes signature in the mature sperm RNA cargo, showing most of them positive translation at pre-cleavage zygote, suggesting that paternally-derived enzymes mRNA cooperate with maternal factors to embryo chromatin assembly. Our study shows several histone modifying enzymes not described yet in spermatogenesis and even more, important mechanistic aspects behind transgenerational epigenetics. Epigenetic enzymes not only can respond to environmental stressors, but could function as vectors of epigenetic information and participate in chromatin organization during maternal-to-zygote transition.

The expression, function, and utilization of Protamine1: a literature review

Objective

Protamine 1 (PRM1) is specific in sperm and plays essential roles in fertilization, also a member of cancer testis antigen (CTA) family. This study aims to summarize the expression and function of PRM1 in spermatogenesis, and to broaden the current knowledge and inspire future development of PRM1-based therapeutic strategies in cancer treatment and nanomedicine.

Background

The protamine proteins, are characterized by an arginine-rich core and cysteine residues. Humans express two types of protamine: PRM1 and PRM2. The abnormal expression or proportion of PRM1 and PRM2 is known to be associated with subfertility and infertility, especially for PRM1 which is highly evolutionary conserved in mammalians and expressed in all vertebrates. Biological functions of PRM1 have been unveiled in diverse cellular processes, such as tumorigenesis, somatic cell nucleus transfer, and drug delivery systems. Moreover, PRM1 is identified as a CTA in chronic leukemia (CLL) and colorectal cancer (CRC).

Methods

Literature was obtained using PubMed and the keywords protamine 1, PRM1, or P1, from January 1, 1980, through July 20, 2021. We also collect the additional evidence through screening references of articles identified through the PubMed searches.

Conclusions

PRM1 is well-studied in male infertility, and further researches and attempts to develop PRM1 as novel tumor marker, as well as drug delivery vector, will be of important clinical significance.

Male reproductive systems of Macaca mulatta: Gonadal development, spermatogenesis and applications in spermatogonia stem cell transplantation

Rhesus macaque (Macaca mulatta) is widely applied in animal model construction of infertility, spermatogonia stem cell transplantation and male reproductive diseases. In this review, we describe the seasonal changes of the reproductive system in rhesus macaques, the regular pattern of spermatogenesis and spermatozoa maturation, and the differentiation of spermatogonia and spermatocytes. The duration of the M. mulatta spermatogenesis is approximately 10 days and seminiferous epithelium cycles mainly consist of 12 stages, which provide a suitable model for reproductive studies in non-human primates. Here, we summarize the features of gonadal development and sperm maturation in the rhesus monkeys, which provide important information in the studies of reproductive biology. Rhesus macaque is an excellent animal model in spermatogonia stem cell transplantation. We discuss the applications and progresses of assisted reproductive technologies in sperm liquefaction, semen cryopreservation and spermatogonia stem cell transplantation of rhesus macaques. Besides, we sort out recent proteomic analyses of male reproductive systems and semen samples in rhesus macaques. This review mainly focuses on male reproductive biology and application studies using M. mulatta, which would promote the development of new therapeutic interventions on assisted reproduction and reproductive disease studies in the future.

Histone Post-Translational Modifications and CircRNAs in Mouse and Human Spermatozoa: Potential Epigenetic Marks to Assess Human Sperm Quality

Spermatozoa (SPZ) are motile cells, characterized by a cargo of epigenetic information including histone post-translational modifications (histone PTMs) and non-coding RNAs. Specific histone PTMs are present in developing germ cells, with a key role in spermatogenic events such as self-renewal and commitment of spermatogonia (SPG), meiotic recombination, nuclear condensation in spermatids (SPT). Nuclear condensation is related to chromatin remodeling events and requires a massive histone-to-protamine exchange. After this event a small percentage of chromatin is condensed by histones and SPZ contain nucleoprotamines and a small fraction of nucleohistone chromatin carrying a landascape of histone PTMs. Circular RNAs (circRNAs), a new class of non-coding RNAs, characterized by a nonlinear back-spliced junction, able to play as microRNA (miRNA) sponges, protein scaffolds and translation templates, have been recently characterized in both human and mouse SPZ. Since their abundance in eukaryote tissues, it is challenging to deepen their biological function, especially in the field of reproduction. Here we review the critical role of histone PTMs in male germ cells and the profile of circRNAs in mouse and human SPZ. Furthermore, we discuss their suggested role as novel epigenetic biomarkers to assess sperm quality and improve artificial insemination procedure.

Effects of cryopreservation on stallion sperm protamine messenger RNAs

Protamines substitute DNA-binding histones during late spermatogenesis in sperm nucleus. Stallion sperm contains all three variants of these arginine-rich and positively charged nuclear proteins (P1, P2 and P3). Two variants of protamine-2, that is P2 and P3, constitute approximately 15% of the entire protamine content. Also, the ratio of protamine-1 to protamine-2 varies among different mammalian species, and abnormal protamine ratios and protamine content are correlated with male infertility. In this study, changes in protamine mRNA abundance for all three protamines were investigated in stallion sperm during cryopreservation. Twelve ejaculates were collected from six sexually mature stallions. Sperm samples were divided into two parts for total mRNA extraction: one as fresh and the other as cryopreserved sample. Levels of three protamine transcripts were determined by real-time reverse transcriptase polymerase chain reaction. Results of relative expression showed that cryopreservation can significantly alter protamine transcripts: protamine 2 was downregulated, while protamine 3 was upregulated in cryopreserved samples relative to the control. Changes in protamine 1 were not significant after cryopreservation. This study is the first to evaluate changes in mRNA abundance of protamine genes in stallion sperm following cryopreservation. Such evaluations are important in finding transcriptomic markers for success in fertilization and assisted reproductive techniques.

CBP/p300 inhibitor C646 prevents high glucose exposure induced neuroepithelial cell proliferation

BACKGROUND

Maternal diabetes related neural tube defects (NTDs) are a result of oxidative stress and apoptosis. However, the molecular mechanism behind the pathogenesis is not fully understood. Here, we report that high glucose exposure-induced epigenetic changes influence histone H4 acetylation and neuroepithelial cell proliferation. We also show that the acetyltransferase inhibitor C646 can prevent high glucose induced changes in histone H4 acetylation and neuroepithelial cell proliferation.

METHODS

By using LC-MS/MS as an unbiased approach, we screened the histone acetylation profile in an E9 neuroepithelial cell line (NE-4C) under high glucose exposure. We further explored the mechanism in cells in vitro and in maternal diabetes-induced mouse embryos in vivo.

RESULTS

We identified 35 core histone acetylation marks in normal E9 neuroepithelial cells, whereas high glucose exposure resulted in novel acetylation sites on H4K31 and H4K44. Acetylation levels of embryonic development associated H4K5/K8/K12/K16 increased in neuroepithelial cells exposed to high glucose in vitro and in brain tissue from maternal diabetes induced exencephalic embryos in vivo. Further, mRNA level of histone acetyltransferase CBP encoded gene Crebbp was significantly increased both in vitro and in vivo. The addition of C646, a selective inhibitor for CBP/p300, significantly rescued increase of H4K5/K8/K12/K16 acetylation levels and H3S10pi-labeled neuroepithelial cell proliferation induced by high glucose exposure.

CONCLUSION

Our data provide complementary insights for potential mechanisms of maternal diabetes induced NTDs.

Ex vivo culture of Drosophila pupal testis and single male germ-line cysts: dissection, imaging, and pharmacological treatment

During spermatogenesis in mammals and in Drosophila melanogaster, male germ cells develop in a series of essential developmental processes. This includes differentiation from a stem cell population, mitotic amplification, and meiosis. In addition, post-meiotic germ cells undergo a dramatic morphological reshaping process as well as a global epigenetic reconfiguration of the germ line chromatin-the histone-to-protamine switch. Studying the role of a protein in post-meiotic spermatogenesis using mutagenesis or other genetic tools is often impeded by essential embryonic, pre-meiotic, or meiotic functions of the protein under investigation. The post-meiotic phenotype of a mutant of such a protein could be obscured through an earlier developmental block, or the interpretation of the phenotype could be complicated. The model organism Drosophila melanogaster offers a bypass to this problem: intact testes and even cysts of germ cells dissected from early pupae are able to develop ex vivo in culture medium. Making use of such cultures allows microscopic imaging of living germ cells in testes and of germ-line cysts. Importantly, the cultivated testes and germ cells also become accessible to pharmacological inhibitors, thereby permitting manipulation of enzymatic functions during spermatogenesis, including post-meiotic stages. The protocol presented describes how to dissect and cultivate pupal testes and germ-line cysts. Information on the development of pupal testes and culture conditions are provided alongside microscope imaging data of live testes and germ-line cysts in culture. We also describe a pharmacological assay to study post-meiotic spermatogenesis, exemplified by an assay targeting the histone-to-protamine switch using the histone acetyltransferase inhibitor anacardic acid. In principle, this cultivation method could be adapted to address many other research questions in pre- and post-meiotic spermatogenesis.

Histone acetylation level and histone acetyltransferase/deacetylase activity in ejaculated sperm from normozoospermic men

PURPOSE

The aim of this work was to evaluate nuclear histone acetylation level and total histone acetyltransferase (HAT) and deacetylase (HDAC) activity in ejaculated sperm and their relevance to conventional sperm parameters.

MATERIALS AND METHODS

Thirty-three normozoospermic men were included in this study. Semen samples were processed by swim-up and then immunostained by six acetylation antibodies (H3K9ac, H3K14ac, H4K5ac, H4K8ac, H4K12ac, and H4K16ac). Our preliminary study verified the expression of HAT/HDAC1 in mature human sperm. From vitrified-warmed sperm samples, total HAT/HDAC activity was measured by commercially available kits. Nuclear DNA integrity was also measured by TUNEL assay.

RESULTS

The levels of six acetylation marks were not related with conventional sperm parameters including sperm DNA fragmentation index (DFI) as well as HAT/HDAC activity. However, sperm DFI was positively correlated with HAT activity (r=0.038 after adjustment, p<0.02). HAT activity showed a negative relationship with HDAC activity (r=-0.51, p<0.01). Strict morphology was negatively correlated with acetylation enzyme index (=HAT activity/HDAC activity) (r=-0.53, p<0.01).

CONCLUSION

Our works demonstrated a significant relationship of acetylation-associated enzyme activity and strict morphology or sperm DFI.

Occurrence of calreticulin during the exchange of nucleohistones into protamine-type proteins in Chara vulgaris spermiogenesis

During spermiogenesis of an alga Chara vulgaris, which resembles that of animals, nucleohistones are replaced by protamine-type proteins. This exchange takes place in a spermatid nucleus during the key V spermiogenesis stage, in which rough endoplasmic reticulum is the site of protamine-type protein synthesis and is also the pathway guiding the proteins to their destination, nucleus. In the present work, it was shown that a chaperon protein, calreticulin (CRT), abundantly present at this significant V stage of spermiogenesis in a few cellular compartments, i.e., a nucleus, lumen of cisternae, and vesicles of significantly swollen ER as well as outside these structures, e.g., in Golgi apparatus, could have taken part in the process of exchange of nuclear proteins. Colocalization of two proteins, protamine-type proteins, crucial for reproduction, and CRT, was especially visible in a nucleus, mainly on its peripheries where condensed chromatin was present. Localization of protamine-type proteins and CRT in nucleus is in agreement with our previous results showing that protamine-type proteins were twofold more labelled in the peripheral area in comparison to the nucleus center occupied by noncondensed chromatin. The role of CRT in the reproduction of both plants and animals is also discussed.

Presence of histone H3 acetylated at lysine 9 in male germ cells and its distribution pattern in the genome of human spermatozoa

During spermatogenesis, approximately 85% of histones are replaced by protamines. The remaining histones have been proposed to carry essential marks for the establishment of epigenetic information in the offspring. The aim of the present study was to analyse the expression pattern of histone H3 acetylated at lysine 9 (H3K9ac) during normal and impaired spermatogenesis and the binding pattern of H3K9ac to selected genes within ejaculates. Testicular biopsies, as well as semen samples, were used for immunohistochemistry. Chromatin immunoprecipitation was performed with ejaculated sperm chromatin. HeLa cells and prostate tissue served as controls. Binding of selected genes was evaluated by semiquantitative and real-time polymerase chain reaction. Immunohistochemistry of H3K9ac demonstrated positive signals in spermatogonia, spermatocytes, elongating spermatids and ejaculated spermatozoa of fertile and infertile men. H3K9ac was associated with gene promoters (CRAT, G6PD, MCF2L), exons (SOX2, GAPDH, STK11IP, FLNA, PLXNA3, SH3GLB2, CTSD) and intergenic regions (TH) in fertile men and revealed shifts of the distribution pattern in ejaculated spermatozoa of infertile men. In conclusion, H3K9ac is present in male germ cells and may play a role during the development of human spermatozoa. In addition, H3K9ac is associated with specific regions of the sperm genome defining an epigenetic code that may influence gene expression directly after fertilisation.

Transition of basic protein during spermatogenesis of Fenneropenaeus chinensis (Osbeck, 1765)

According to the ultrastructural characteristic observation of the developing male germ cells, spermatogenesis of the crustacean shrimp, Fenneropenaeus chinensis, is classified into spermatogonia, primary spermatocytes, secondary spermatocyte, four stages of spermatids, and mature sperm. The basic protein transition during its spermatogenesis is studied by transmission electron microscopy of ammoniacal silver reaction and immunoelectron microscopical distribution of acetylated histone H4. The results show that basic protein synthesized in cytoplasm of spermatogonia is transferred into the nucleus with deposition on new duplicated DNA. In the spermatocyte stage, some nuclear basic protein combined with RNP is transferred into the cytoplasm and is involved in forming the cytoplasmic vesicle clumps. In the early spermatid, most of the basic protein synthesized in the new spermatid cytoplasm is transferred into the nucleus, and the chromatin condensed gradually, and the rest is shifted into the pre-acrosomal vacuole. In the middle spermatid, the nuclear basic protein linked with DNA is acetylated and transferred into the proacrosomal vacuole and assembled into the acrosomal blastema. At the late spermatid, almost all of the basic protein in the nucleus has been removed into the acrosome. During the stage from late spermatid to mature sperm, some de novo basic proteins synthesized in the cytoplasm belt transfer into the nucleus without a membrane and almost all deposit in the periphery to form a supercoating. The remnant histone H4 accompanied by chromatin fibers is acetylated in the center of the nucleus, leading to relaxed DNA and activated genes making the nucleus non-condensed.

The interaction of modified histones with the bromodomain testis-specific (BRDT) gene and its mRNA level in sperm of fertile donors and subfertile men

As histone modifications have been suggested to be involved in the regulation of gene expression after fertilisation, the present study aimed to analyze the interaction between the bromodomain testis-specific (BRDT) gene and differentially modified histones in human spermatozoa. The BRDT transcript level was studied to identify possible correlations between epigenetic changes, mRNA level and subfertility associated with impaired sperm chromatin condensation. Chromatin immunoprecipitation (ChIP) was performed with ejaculates from fertile and subfertile men using antibodies against specifically acetylated and methylated histone H3. Immunoprecipitated DNA was analysed by real-time quantitative PCR with primer pairs for BRDT. The BRDT mRNA level was screened by real-time RT-PCR. ChIP assay revealed co-localisation of acetylated and methylated histones within promoter and exon regions of the BRDT gene in fertile men. Interestingly, reduced binding of investigated modified histone modifications was observed in the BRDT promoter of subfertile patients. Different mRNA levels of BRDT have been detected in a group of infertile patients, as well as in fertile men. Enrichment of methylated histones within the BRDT promoter of fertile sperm suggests that this epigenetic mark may cause repression of BRDT after fertilisation, and may be changed in infertile patients. Our data suggest that reduced histone methylation in the promoter of BRDT may be associated with increased transcript levels in subfertile patients.

Histone H4 acetylation is essential to proceed from a histone- to a protamine-based chromatin structure in spermatid nuclei of Drosophila melanogaster

In humans, other mammals, and also in Drosophila, the paternal genome in the sperm is highly condensed and organized mainly in a protamine-based chromatin structure. However, the timing and mechanism of the switch from a histone- to the protamine-based chromatin configuration is still poorly understood. We therefore established Drosophila in vitro cultures of cysts with 64 synchronously developing spermatids genetically marked with histone H2AvD-RFP and ProtamineB-eGFP. Live cell imaging showed that the switch from H2AvD-RFP to Protamine-eGFP chromatin takes approximately five hours, with a short but clear overlap of the presence of both histones and protamines. Moreover, cultured pupal testes showed H4 hyperacetylation at the canoe stage shortly before histone removal; a feature previously observed in the intact animal. We then used TSA to inhibit histone deacetylation and found that premature hyperacetylation was already induced at the round nuclei stage of spermatids. However, this premature hyperacetylation did not lead to a premature switch to the protamine-based chromatin structure, showing that histone hyperacetylation is not the sole inducer of the histone to protamine switch. Importantly, we observed that inactivation of histone acetyltransferases by anacardic acid blocks further differentiation and thus prevents the degradation of histones and the switch to a protamine-based chromatin. Thus, we conclude that H4 hyperacetylation is an essential feature but not the sole inducer of the histone to protamine switch during spermiogenesis.