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

The emerging role of circRNAs on skeletal muscle development in economical animals

CircRNAs are a novel type of closed circular molecules formed through a covalent bond lacking a 5'cap and 3' end tail, which mainly arise from mRNA precursor. They are widely distributed in plants and animals and are characterized by stable structure, high conservativeness in cells or tissues, and showed the expression specificity at different stages of development in different tissues. CircRNAs have been gradually attracted wide attention with the development of RNA sequencing, which become a new research hotspot in the field of RNA. CircRNAs play an important role in gene expression regulation. Presently, the related circRNAs research in the regulation of animal muscle development is still at the initial stage. In this review, the formation, properties, biological functions of circRNAs were summarized. The recent research progresses of circRNAs in skeletal muscle growth and development from economic animals including livestock, poultry and fishes were introduced. Finally, we proposed a prospective for further studies of circRNAs in muscle development, and we hope our research could provide new ideas, some theoretical supports and helps for new molecular genetic markers exploitation and animal genetic breeding in future.

Expression profiles of circular RNAs in spermatozoa from aging men

BACKGROUND

Advanced paternal age (APA) is associated with decreased fertility, but the mechanism underlying APA remains unknown. CircRNAs have been reported to be ideal candidate biomarkers for diagnostic and therapeutic applications in many diseases and are also involved in spermatogenesis. Hence, we aimed to assess the circRNA expression profile of spermatozoa from aging men.

METHODS AND RESULTS

We recruited 6 subjects, including 3 in the younger group (men age < 40) and 3 in the APA group (men age ≥ 40). RNA sequencing was exploited to identify the expression profiles of circRNAs between the two groups. The expression levels of circRNAs were validated using real-time quantitative polymerase chain reaction (RT-qPCR). Kyoto Encyclopedia of Genes and Genomes biological pathway analysis and Gene Ontology analysis were performed to evaluate the functions of differentially expressed circRNAs (DE-circRNAs) between the two groups. In total, 18,787 circRNAs were sequenced in the spermatozoa of two groups. Our analysis revealed that there were 1056 downregulated circRNAs and 1228 upregulated circRNAs between the two groups, and KEGG analysis showed they were mainly involved in pathways including the DNA repair signaling pathway, meiotic recombination signaling pathway, and PI3K/AKT signaling pathway.

CONCLUSIONS

In conclusion, our study suggested that circRNAs play a vital role in spermatozoa from aging men and provided a fresh perspective on the specific regulatory mechanism of spermatozoa from aging men.

Oxidative stress-induced apoptosis and autophagy: Balancing the contrary forces in spermatogenesis

Spermatogenesis is a complex process in the testis and is a cornerstone of male infertility. The abundance of unsaturated fatty acid and high cell division rate make male germs cells prone to DNA deterioration. ROS-mediated oxidative stress triggers DNA damage, autophagy, and apoptosis in male germ cells, which are critical causative factors that lead to male infertility. The complex connection and molecular crosstalk between apoptosis and autophagy is seen at multifaceted levels that interconnect the signaling pathways of these two processes. Multilevel interaction between apoptosis and autophagy is a seamless state of survival and death in response to various stressors. Interaction between multiple genes and proteins such as the mTor signaling pathway, Atg12 proteins, and the death adapter proteins, such as Beclin 1, p53, and Bcl-2 family proteins, validates such a link between these two phenomena. Testicular cells being epigenetically different from somatic cells, undergo numerous significant epigenetic transitions, and ROS modulates the epigenetic framework of mature sperm. Epigenetic deregulation of apoptosis and autophagy under oxidative stress conditions can cause sperm cell damage. The current review recapitulates the current role of prevailing stressors that generate oxidative stress leading to the induction of apoptosis and autophagy in the male reproductive system. Considering the pathophysiological consequences of ROS-mediated apoptosis and autophagy, a combinatorial approach, including apoptosis inhibition and autophagy activation, a therapeutic strategy to treat male idiopathic infertility. Understanding the crosslink between apoptosis and autophagy under stress conditions in male germ cells may play an essential role in developing therapeutic strategies to treat infertility.

Biological functions of circRNAs and their advance on skeletal muscle development in bovine

The development of skeletal muscle in animals is a complex biological process, which are strictly and precisely regulated by many genes and non-coding RNAs. Circular RNA (circRNA) was found as a novel class of functional non-coding RNA with ring structure in recent years, which appears in the process of transcription and is formed by covalent binding of single-stranded RNA molecules. With the development of sequencing and bioinformatics analysis technology, the functions and regulation mechanisms of circRNAs have attracted great attention due to its high stability characteristics. The role of circRNAs in skeletal muscle development have been gradually revealed, where circRNAs were involved in various biological processes, such as proliferation, differentiation, and apoptosis of skeletal muscle cells. In this review, we summarized the current studies advance of circRNAs involved in skeletal muscle development in bovine, and hope to gain a deeper understanding of the functional roles of the circRNAs in muscle growth. Our results will provide some theoretical supports and great helps for the genetic breeding of this species, and aiming at improving bovine growth and development and preventing muscle diseases.

Impacts of disinfection byproduct exposures on male reproductive health: Current evidence, possible mechanisms and future needs

Disinfection byproducts (DBPs) are a class of ubiquitous chemicals in drinking water and inevitably result in widespread human exposures. Potentially adverse health effects of DBP exposures, including reproductive and developmental outcomes, have been increasing public concerns. Several reviews have focused on the adverse pregnancy outcomes of DBPs. This review summarized current evidence on male reproduction health upon exposure to DBPs from toxicological and epidemiological literature. Based on existing experimental studies, there are sufficient evidence showing that haloacetic acids (HAAs) are male reproductive toxicants, including reduced epididymal weight, decreased semen parameters and sperm protein 22, and declined testosterone levels. However, epidemiological evidence remains insufficient to support a link of DBP exposures with adverse male reproductive outcomes, despite that blood and urinary DBP biomarkers are associated with decreased semen quality. Eight potential mechanisms, including germ/somatic cell dysfunction, oxidative stress, genotoxicity, inflammation, endocrine hormones, folate metabolism, epigenetic alterations, and gut microbiota, are likely involved in male reproductive toxicity of DBPs. We also identified knowledge gaps in toxicological and epidemiological studies to enhance future needs.

Cannabis and Paternal Epigenetic Inheritance

Cannabis is the most widely used illicit drug in Western counties and its abuse is particularly high in male adolescents and young adults. Its main psychotropic component, the cannabinoid delta-9-tetrahydrocannabinol (Δ⁹-THC), interferes in the endogenous endocannabinoid system. This signaling system is involved in the control of many biological activities, including the formation of high-quality male gametes. Direct adverse effects of Δ⁹-THC in male reproduction are well known in both animal models and humans. Nevertheless, the possibility of long-term effects due to epigenetic mechanisms has recently been reported. In this review, we summarize the main advances in the field suggesting the need to pay attention to the possible long-term epigenetic risks for the reproductive health of cannabis users and the health of their offspring.

Sperm RNA Payload: Implications for Intergenerational Epigenetic Inheritance

There is mounting evidence that ancestral life experiences and environment can influence phenotypes in descendants. The parental environment regulates offspring phenotypes potentially via modulating epigenetic marks in the gametes. Here, we review examples of across-generational inheritance of paternal environmental effects and the current understanding of the role of small RNAs in such inheritance. We discuss recent advances in revealing the small RNA payload of sperm and how environmental conditions modulate sperm small RNAs. Further, we discuss the potential mechanism of inheritance of paternal environmental effects by focusing on sperm small RNA-mediated regulation of early embryonic gene expression and its role in influencing offspring phenotypes.

Male Infertility: A Review of Key Papers Appearing in the Reproductive Medicine and Andrology Section of the Journal of Clinical Medicine

Male infertility accounts for 30% of infertility cases and its prevalence in the general population approximately ranges between 9 and 15%, according to the available surveys [...].

Epigenetic markers in the embryonal germ cell development and spermatogenesis

Spermatogenesis is the process of generation of male reproductive cells from spermatogonial stem cells in the seminiferous epithelium of the testis. During spermatogenesis, key spermatogenic events such as stem cell self-renewal and commitment to meiosis, meiotic recombination, meiotic sex chromosome inactivation, followed by cellular and chromatin remodeling of elongating spermatids occur, leading to sperm cell production. All the mentioned events are at least partially controlled by the epigenetic modifications of DNA and histones. Additionally, during embryonal development in primordial germ cells, global epigenetic reprogramming of DNA occurs. In this review, we summarized the most important epigenetic modifications in the particular stages of germ cell development, in DNA and histone proteins, starting from primordial germ cells, during embryonal development, and ending with histone-to-protamine transition during spermiogenesis.

Identification and analysis of differentially expressed (DE) circRNA in epididymis of yak and cattleyak

Circular RNAs (circRNAs), as endogenous non-coding RNA with unique closed ring structure, is closely related to animal reproduction, and understanding the expression of circRNA in yak and cattleyak epididymal tissues is of great significance for understanding cattleyak sterility. Based on this, we screened and identified the differentially expressed circRNA in the epididymis of three yaks and two cattleyak. A total of 1,298 circRNAs were identified in the epididymis of yak and cattleyak, of which 137 differentially expressed (DE) circRNAs and the functions of some of them were elucidated in this research, as well as qPCR verification to 6 circRNAs from the 137 DE circRNAs. Gene Ontology (GO) enrichment analysis suggested that DE circRNAs were mainly related to metabolic process, development process, immune system process, reproductive process, reproduction, biological adhesion and growth. COG classification analysis showed that the DE circRNAs derived genes were mainly related to replication, recombination and repair. KEGG pathway analysis suggested that DE circRNAs were mainly involved in RNA degradation. In addition, we also screened Bta-mir-103, which is a circRNA binding miRNA related to sperm activity.

Epigenetics Role in Spermatozoa Function: Implications in Health and Evolution-An Overview

The unique properties of spermatozoa are established through the spermatogenesis and maturation processes concurrently with its epigenome. It is known that damage to epigenetic mechanisms can lead to reproductive problems. However, scientific reviews addressing the role of the spermatozoa epigenome during the reproductive process are scarce. Therefore, the aim of this review was to offer a detailed overview of current knowledge in the field of spermatozoa epigenetics and its consequent implications. A full search was performed through three databases by combining five keywords. Inclusion criteria were implemented to grant accessibility, relevance, and concretion. Besides, some articles were manually removed or added to obtain an adequate and complete collection of 485 scientific publications. This compilation was used to conduct the bibliometric analysis and the data review separately. Bibliometric results displayed that spermatozoa epigenetics is an active and growing research area. The bibliographic overview showed that sperm epigenome correlates with the development of its function, explaining the environmental influence on reproductive pathologies or abnormal inheritance. The main conclusions were that the normal performance of sperm is heavily reliant on its epigenetics and that this study area is burgeoning, with the potential ability to provide society with clinical innovations in a short-term period.

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.

circRNA-miRNA-mRNA network analysis to explore the pathogenesis of abnormal spermatogenesis due to aberrant m6A methylation

Many studies have shown that circRNAs and miRNAs play important roles in many different life processes. However, the function of circRNAs in spermatogenesis remains unknown. Here, we aimed to explore the mechanisms whereby circRNA-miRNAs-mRNAs regulate abnormal m6A methylation in GC-1spg spermatogonia. We first reduced m6A methylation in GC-1spg whole cells after knocking down the m6A methyltransferase enzyme, METTL3. Then, we performed circRNA- and miRNA-seq on GC-1spg cells with low m6A methylation and identified 48 and 50 differentially expressed circRNAs and miRNAs, respectively. We also predicted the targets of the differentially expressed miRNAs by using Miranda software and further constructed the differentially expressed circRNA-differentially expressed miRNA-mRNA ceRNA network. GO analysis was performed on the differentially expressed circRNAs and miRNA-targeted mRNAs, and an interaction network between the proteins of interest was constructed using Cytoscape. The final GO analysis showed that the target mRNAs were involved in sperm formation. Therefore, a PPI network was subsequently constructed and 2 hub genes (H2afx and Dnmt3a) were identified. In this study, we constructed a ceRNA network and explored the regulatory roles of circRNAs and miRNAs in the pathogenesis of abnormal spermatogenesis caused by low levels of methylated m6A. Also, we identified two pivotal genes that may be key factors in infertility caused by abnormal m6A methylation. This may provide some ideas for the treatment of infertility resulting from abnormal spermatogenesis.

Cytochalasin D restores nuclear size acting on F-actin and IZUMO1 localization in low-quality spermatozoa

In spermatozoa, the nuclear F-actin supports the acroplaxome, a subacrosomal structure involved in the correct exposure of several acrosomal membrane proteins; among them, the glycoprotein IZUMO1 is the major protein involved in sperm-oocyte fusion. Nuclear F-actin is also involved in sperm head shaping and chromosome compartmentalization. To date, few notions regarding the bivalent role of F-actin on sperm chromatin organization and IZUMO1 positioning have been reported. In our work, we characterized subcellular organization of F-actin in human high- and low-quality spermatozoa (A- and B-SPZ), respectively, showing that F-actin over-expression in sperm head of B-SPZ affected IZUMO1 localization. A correct IZUMO1 repositioning following in vitro induction of F-actin depolymerization, by cytochalasin D treatment, occurred. Interestingly, F-actin depolymerization was also associated with a correct acrosome repositioning, thus to favor a proper acrosome reaction onset, with changes in sperm nuclear size parameters and histone acetylation rate reaching high-quality conditions. In conclusion, the current work shows a key role of F-actin in the control of IZUMO1 localization as well as chromatin remodeling and acetylation events.

Actin remodeling driven by circLIMA1: sperm cell as an intriguing cellular model

CircRNA cargo in spermatozoa (SPZ) participates in setting cell quality, in terms of morphology and motility. Cannabinoid receptor CB1 activity is correlated with a proper spermatogenesis and epididymal sperm maturation. Despite CB1 promotes endogenous skill to circularize mRNAs in SPZ, few notions are reported regarding the functional link between endocannabinoids and spermatic circRNA cargo. In CB1 knock-out male mice, we performed a complete dataset of spermatic circRNA content by microarray strategy.

Differentially expressed (DE)-circRNAs, as a function of genotype, were identified. Within DE-circRNAs, we focused the attention on circLIMA1, as putative actin-cytoskeleton architecture regulator. The validation of circLIMA1 dependent-competitive endogenous RNA (ceRNA) network (ceRNET) in in vitro cell line confirmed its activity in the regulation of the cytoskeletal actin. Interestingly, a dynamic actin regulation in SPZ nuclei was found during their epididymal maturation.

In this scenario, we showed for the first time an intriguing sperm nuclear actin remodeling, regulated via a ceRNET-independent pathway, consisting in the nuclear shuttling of circLIMA1-QKI interactome and downstream in Gelsolin regulation. In particular, the increased levels of circLIMA1 in CB1 knock-out SPZ, associated with an inefficient depolymerization of nuclear actin, specifically illustrate how endocannabinoids, by regulating circRNA cargo, may contribute to sperm morpho-cellular maturation.

KISS1R and ANKRD31 Cooperate to Enhance Leydig Cell Gene Expression via the Cytoskeletal-Nucleoskeletal Pathway

Kisspeptins are involved in the regulation of hypothalamic-pituitary-gonadal axis, Leydig cell functions, and testosterone secretion, acting as endogenous ligands of the KISS1 receptor. ANKRD31 protein participates in male fertility, regulating meiotic progression, and epididymal sperm maturation. Here, we show that in Leydig cells, KISS1 receptor and ANKRD31 proteins physically interact; the formation of this protein complex is enhanced by Kisspeptin-10 that also modulates F-actin synthesis, favoring histone acetylation in chromatin and gene expression via the cytoskeletal–nucleoskeletal pathway. Kp/KISS1R system deregulation, expression impairment of cytoskeletal–nucleoskeletal mediators, Leydig gene targets, and the decreased testosterone secretion in Ankrd31^−/− testis strongly supported our hypothesis. Furthermore, cytochalasin D treatment subverted the gene expression induction dependent on Kisspeptin-10 action. In conclusion, the current work highlights a novel role for the Kisspeptin-10 in the induction of the cytoskeletal–nucleoskeletal route, downstream a physical interaction between KISS1 receptor and ANKRD31, with gene expression activation as final effect, in Leydig cells.

Potential and functional prediction of six circular RNAs as diagnostic markers for colorectal cancer

Background

Circular RNAs (circRNAs) have been discovered in colorectal cancer (CRC), but there are few reports on the expression distribution and functional mining analysis of circRNAs.

Methods

Differentially expressed circRNAs in CRC tissues and adjacent normal tissues were screened and identified by microarray and qRT-PCR. ROC curves of the six circRNAs were analyzed. A series of bioinformatics analyses on differentially expressed circRNAs were performed.

Results

A total of 207 up-regulated and 357 down-regulated circRNAs in CRC were screened, and three top up-regulated and down-regulated circRNAs were chosen to be verified in 33 pairs of CRCs by qRT-PCR. 6 circRNAs showed high diagnostic values (AUC = 0.6860, AUC = 0.8127, AUC = 0.7502, AUC = 0.9945, AUC = 0.9642, AUC = 0.9486 for hsa_circRNA_100833, hsa_circRNA_103828, hsa_circRNA_103831 and hsa_circRNA_103752, hsa_circRNA_071106, hsa_circRNA_102293). A circRNA-miRNA-mRNA regulatory network (cirReNET) including six candidate circRNAs, 19 miRNAs and 210 mRNA was constructed, and the functions of the cirReNET were predicted and displayed via Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses on these mRNAs and protein-protein interaction (PPI) network of the hub genes acquired by string and CytoHubba.

Conclusion

A cirReNET containing potential diagnostic and predictive indicators of CRCs and several critical circRNA-miRNA-mRNA regulatory axes (cirReAXEs) in CRC were mined, and may provide a novel route to study the mechanism and clinical targets of CRC.

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.

Epigenetic Modifications, A New Approach to Male Infertility Etiology: A Review

Recent studies have indicated that epigenetic alterations are critical for normal function and development of spermatozoa during the fertilization process. This review will focus on the latest advances in epigenome profiling of the chromatin modifications during sperm development, as well as the potential roles of epigenetic mechanisms in the context of male infertility. In this review, all data were collected from published studies that considered the effect of epigenetic abnormalities on human spermatogenesis, sperm parameters quality, fertilization process, embryo development and live births. The database PubMed was searched for all experimental and clinical studies using the Keywords "epigenetic modifications", "male infertility", "spermatogenesis", "embryo development" and "reproductive function". Post-translational modifications of histone, DNA methylations and chromatin remodeling are among the most common forms of epigenetic modifications that regulate all stages of spermatogenesis and fertilization process. Incorrect epigenetic modifications of certain genes involved in the spermatogenesis and sperm maturation may be a main reason of male reproductive disorder and infertility. Most importantly, abnormal patterns of epigenetic modifications or transgenerational phenotypes and miRNAs expression may be transmitted from one generation to the next through assisted reproductive techniques (ART) and cause an increased risk of birth defects, infertility and congenital anomalies in children. Epigenetic modifications must be considered as a one of the main factors of unexplained male infertility etiology. Due to high risk of transmitting incorrect primary imprints to offspring, there is a need for more research into epigenetic alterations in couples who benefit of ART support.

FUS driven circCNOT6L biogenesis in mouse and human spermatozoa supports zygote development

Circular RNA (circRNA) biogenesis requires a backsplicing reaction, promoted by inverted repeats in cis-flanking sequences and trans factors, such as RNA-binding proteins (RBPs). Among these, FUS plays a key role. During spermatogenesis and sperm maturation along the epididymis such a molecular mechanism has been poorly explored. With this in mind, we chose circCNOT6L as a study case and wild-type (WT) as well as cannabinoid receptor type-1 knock-out (Cb1^−/−) male mice as animal models to analyze backsplicing mechanisms. Our results suggest that spermatozoa (SPZ) have an endogenous skill to circularize mRNAs, choosing FUS as modulator of backsplicing and under CB1 stimulation. A physical interaction between FUS and CNOT6L as well as a cooperation among FUS, RNA Polymerase II (RNApol2) and Quaking (QKI) take place in SPZ. Finally, to gain insight into FUS involvement in circCNOT6L biogenesis, FUS expression was reduced through RNA interference approach. Paternal transmission of FUS and CNOT6L to oocytes during fertilization was then assessed by using murine unfertilized oocytes (NF), one-cell zygotes (F) and murine oocytes undergoing parthenogenetic activation (PA) to exclude a maternal contribution. The role of circCNOT6L as an active regulator of zygote transition toward the 2-cell-like state was suggested using the Embryonic Stem Cell (ESC) system. Intriguingly, human SPZ exactly mirror murine SPZ.

Small Noncoding RNAs in Reproduction and Infertility

Infertility has been reported as one of the most common reproductive impairments, affecting nearly one in six couples worldwide. A large proportion of infertility cases are diagnosed as idiopathic, signifying a deficit in information surrounding the pathology of infertility and necessity of medical intervention such as assisted reproductive therapy. Small noncoding RNAs (sncRNAs) are well-established regulators of mammalian reproduction. Advanced technologies have revealed the dynamic expression and diverse functions of sncRNAs during mammalian germ cell development. Mounting evidence indicates sncRNAs in sperm, especially microRNAs (miRNAs) and transfer RNA (tRNA)-derived small RNAs (tsRNAs), are sensitive to environmental changes and mediate the inheritance of paternally acquired metabolic and mental traits. Here, we review the critical roles of sncRNAs in mammalian germ cell development. Furthermore, we highlight the functions of sperm-borne sncRNAs in epigenetic inheritance. We also discuss evidence supporting sncRNAs as promising biomarkers for fertility and embryo quality in addition to the present limitations of using sncRNAs for infertility diagnosis and treatment.

Dynamics of hyperacetylated histone H4 (H4Kac) during spermatogenesis in four decapod crustaceans

During spermatogenesis, the transition from histone to protamine is highly conserved in most invertebrates and vertebrates. Thus far, a large and growing body of literature has demonstrated that histones and histone modifications still exist in the sperm nucleus of decapod crustaceans. H4Kac is believed to play an important role in the process of sperm chromatin condensation. However, the dynamics of hyperacetylated histone H4 (H4Kac) during spermatogenesis in decapoda are still unknown. In this paper, the distribution of H4Kac in four decapod crustaceans (Eriocheir sinensis, Charybdis japonica, Procambarus clarkii, and Macrobrachium nipponense) were investigated via immunofluorescence. Our results indicated that H4Kac was visible in the mature sperm nucleus of E. sinensis, C. japonica, and M. nipponense. Unlike the other three species, H4Kac was translocated from the nuclei to cytoplasm in mid-spermatids of P. clarkii. Eventually, H4Kac were not present in mature spermatozoa of P. clarkii. Importantly, we observed for the first time that H4Kac was distributed outside the nucleus, which reminds us that H4Kac may participate in the formation of acrosome structure in decapod crustaceans and may be a prerequisite for proper chromatin decondensation.

Ankrd31 in Sperm and Epididymal Integrity

Ankyrin proteins (ANKRD) are key mediators linking membrane and sub-membranous cytoskeletal proteins. Recent findings have highlighted a new role of ANKRD31 during spermatogenesis, elucidating its involvement in meiotic recombination and male germ cell progression. Following testicular differentiation, spermatozoa (SPZ) enter into the epididymis, where they undergo several biochemical and enzymatic changes. The epididymal epithelium is characterized by cell-to-cell junctions that are able to form the blood-epididymal barrier (BEB). This intricate epithelial structure provides the optimal microenvironment needed for epididymal sperm maturation. To date, no notions have been reported regarding a putative role of ANKRD31 in correct BEB formation. In our work, we generated an Ankrd31 knockout male mouse model (Ankrd31^–/–) and characterized its reproductive phenotype. Ankrd31^–/– mice were infertile and exhibited oligo-astheno-teratozoospermia (a low number of immotile SPZ with abnormal morphological features). In addition, a complete deregulation of BEB was found in Ankrd31^–/–, due to cell-to-cell junction anomalies. In order to suggest that BEB deregulation may depend on Ankrd31 gene deletion, we showed the physical interaction among ANKRD31 and some epithelial junction proteins in wild-type (WT) epididymides. In conclusion, the current work shows a key role of ANKRD31 in the control of germ cell progression as well as sperm and epididymal integrity.

CRISP2, CATSPER1 and PATE1 Expression in Human Asthenozoospermic Semen

The etiology of human asthenozoospermia is multifactorial. The need to unveil molecular mechanisms underlying this state of infertility is, thus, impelling. Circular RNAs (circRNAs) are involved in microRNA (miRNA) inhibition by a sponge activity to protect mRNA targets. All together they form the competitive endogenous RNA network (ceRNET). Recently, we have identified differentially expressed circRNAs (DE-circRNAs) in normozoospermic and asthenozoospermic patients, associated with high-quality (A-spermatozoa) and low-quality (B-spermatozoa) sperm. Here, we carried out a differential analysis of CRISP2, CATSPER1 and PATE1 mRNA expression in good quality (A-spermatozoa) and low quality (B-spermatozoa) sperm fractions collected from both normozoospermic volunteers and asthenozoospermic patients. These sperm fractions are usually separated on the basis of morphology and motility parameters by a density gradient centrifugation. B-spermatozoa showed low levels of mRNAs. Thus, we identified the possible ceRNET responsible for regulating their expression by focusing on circTRIM2, circEPS15 and circRERE. With the idea that motility perturbations could be rooted in quantitative changes of transcripts in sperm, we evaluated circRNA and mRNA modulation in A-spermatozoa and B-spermatozoa after an oral amino acid supplementation known to improve sperm motility. The profiles of CRISP2, CATSPER1 and PATE1 proteins in the same fractions of sperm well matched with the transcript levels. Our data may strengthen the role of circRNAs in asthenozoospermia and shed light on the molecular pathways linked to sperm motility regulation.

Altered Gene Expression in the Testis of Infertile Patients with Nonobstructive Azoospermia

Background

The molecular mechanism of nonobstructive azoospermia (NOA) remains unclear. The aim of this study was to identify gene expression changes in NOA patients and to explore potential biomarkers and therapeutic targets.

Methods

The gene expression profiles of GSE45885 and GSE145467 were collected from the Gene Expression Omnibus (GEO) database, and the differences between NOA and normal spermatogenesis were analyzed. Enrichment analysis was performed to explore biological functions for common differentially expressed genes (DEGs) in GSE45885 and GSE145467. Coexpression analysis of DEGs in GSE45885 was performed, and two modules with the highest correlation with NOA were screened. Key genes were then screened from the intersection genes of the two modules and common DEGs and PPI network. The expression of key genes was validated by quantitative real-time polymerase chain reaction (qRT-PCR) experiments. Finally, through miRTarBase, miRDB, and RAID, the miRNAs were predicted to regulate key genes, respectively.

Results

A total of 345 common DEGs were identified and they were mainly related to spermatogenesis, insulin signaling pathway. Coexpression analysis of DEGs in GSE45885 yielded eight modules; MEblack and MEturquoise had the highest correlation with NOA. Six genes in MEturquoise and RNF141 in MEblack were identified as key genes. qRT-PCR experiments validated the differential expression of key genes between NOA and control. Furthermore, RNF141 was regulated by the largest number of miRNAs.

Conclusion

Our findings suggest that the significant change expression of key genes may be potential markers and therapeutic targets of NOA and may have some impact on the development of NOA.

LINCking the Nuclear Envelope to Sperm Architecture

Nuclear architecture undergoes an extensive remodeling during spermatogenesis, especially at levels of spermatocytes (SPC) and spermatids (SPT). Interestingly, typical events of spermiogenesis, such as nuclear elongation, acrosome biogenesis, and flagellum formation, need a functional cooperation between proteins of the nuclear envelope and acroplaxome/manchette structures. In addition, nuclear envelope plays a key role in chromosome distribution. In this scenario, special attention has been focused on the LINC (linker of nucleoskeleton and cytoskeleton) complex, a nuclear envelope-bridge structure involved in the connection of the nucleoskeleton to the cytoskeleton, governing mechanotransduction. It includes two integral proteins: KASH- and SUN-domain proteins, on the outer (ONM) and inner (INM) nuclear membrane, respectively. The LINC complex is involved in several functions fundamental to the correct development of sperm cells such as head formation and head to tail connection, and, therefore, it seems to be important in determining male fertility. This review provides a global overview of the main LINC complex components, with a special attention to their subcellular localization in sperm cells, their roles in the regulation of sperm morphological maturation, and, lastly, LINC complex alterations associated to male infertility.

Circular RNAs: Novel potential regulators in embryogenesis, female infertility, and pregnancy-related diseases

Circular RNAs (circRNAs) are endogenous noncoding RNAs with unique cyclic structures. Although they were previously considered as nonfunctional transcription byproducts, numerous studies have demonstrated that circRNAs regulate gene transcription and expression via different mechanisms. Reproductive health influences the quality of life and affects offspring propagation in women. CircRNAs have been found to modify pregnancy-related diseases, gynecologic cancers, polycystic ovary syndrome, aging, gamete, and embryo development. It's promising for circRNAs to be the novel diagnostic and therapeutic targets for multiple reproductive diseases. With the widespread application of assisted reproduction technology (ART), it has been revealed that circRNA identification contributes to estimating the quality of gametes and embryos, reflecting the success rate of ART. CRISPR-Cas9 gene editing technology has enabled the discovery of new roles of circRNAs. So far, the roles of circRNAs in the reproductive system remain poorly defined. In this review, we describe the classification and functions of circRNAs in embryogenesis and the female reproductive system diseases, revealing potential roles of circRNAs physiologically and pathologically. In so-doing, we provide ideas for developing circRNA-based therapeutic treatment and clinical application of various female reproductive system diseases.

Characterization of Estrogenic Activity and Site-Specific Accumulation of Bisphenol-A in Epididymal Fat Pad: Interfering Effects on the Endocannabinoid System and Temporal Progression of Germ Cells

The objective of this work has been to characterize the estrogenic activity of bisphenol-A (BPA) and the adverse effects on the endocannabinoid system (ECS) in modulating germ cell progression. Male offspring exposed to BPA during the foetal-perinatal period at doses below the no-observed-adverse-effect-level were used to investigate the exposure effects in adulthood. Results showed that BPA accumulates specifically in epididymal fat rather than in abdominal fat and targets testicular expression of 3β-hydroxysteroid dehydrogenase and cytochrome P450 aromatase, thus promoting sustained increase of estrogens and a decrease of testosterone. The exposure to BPA affects the expression levels of some ECS components, namely type-1 (CB1) and type-2 cannabinoid (CB2) receptor and monoacylglycerol-lipase (MAGL). Furthermore, it affects the temporal progression of germ cells reported to be responsive to ECS and promotes epithelial germ cell exfoliation. In particular, it increases the germ cell content (i.e., spermatogonia while reducing spermatocytes and spermatids), accelerates progression of spermatocytes and spermatids, promotes epithelial detachment of round and condensed spermatids and interferes with expression of cell–cell junction genes (i.e., zonula occcludens protein-1, vimentin and β-catenin). Altogether, our study provides evidence that early exposure to BPA produces in adulthood sustained and site-specific BPA accumulation in epididymal fat, becoming a risk factor for the reproductive endocrine pathways associated to ECS.

Novel circRNA discovery in sheep shows evidence of high backsplice junction conservation

Circular RNAs (circRNAs) are covalently closed circular non-coding RNAs. Due to their structure, circRNAs are more stable and have longer half-lives than linear RNAs making them good candidates for disease biomarkers. Despite the scientific relevance of these molecules, the study of circRNAs in non-model organisms is still in its infancy. Here, we analyse total RNA-seq data to identify circRNAs in sheep from peripheral blood mononuclear cells (PBMCs) and parietal lobe cortex. Out of 2510 and 3403 circRNAs detected in parietal lobe cortex and in PBMCs, a total of 1379 novel circRNAs were discovered. Remarkably, around 63% of all detected circRNAs were found to be completely homologous to a circRNA annotated in human. Functional enrichment analysis was conducted for both tissues based on GO terms and KEGG pathways. The enriched terms suggest an important role of circRNAs from encephalon in synaptic functions and the involvement of circRNAs from PBMCs in basic immune system functions. In addition to this, we investigated the role of circRNAs in repetitive vaccination experiments via differential expression analysis and did not detect any significant relationship. At last, our results support both the miRNA sponge and the miRNA shuttle functions of CDR1-AS in sheep brain. To our knowledge, this is the first study on circRNA annotation in sheep PBMCs or parietal lobe cortex samples.

Mitochondrial Reactive Oxygen Species (ROS) Production Alters Sperm Quality

Besides ATP production, mitochondria are key organelles in several cellular functions, such as steroid hormone biosynthesis, calcium homoeostasis, intrinsic apoptotic pathway, and the generation of reactive oxygen species (ROS). Despite the loss of the majority of the cytoplasm occurring during spermiogenesis, mammalian sperm preserves a number of mitochondria that rearrange in a tubular structure at the level of the sperm flagellum midpiece. Although sperm mitochondria are destroyed inside the zygote, the integrity and the functionality of these organelles seem to be critical for fertilization and embryo development. The aim of this review was to discuss the impact of mitochondria-produced ROS at multiple levels in sperm: the genome, proteome, lipidome, epigenome. How diet, aging and environmental pollution may affect sperm quality and offspring health—by exacerbating oxidative stress—will be also described.

Kisspeptins, new local modulators of male reproduction: A comparative overview

Spermatogenesis is a complex process that leads to the production of male gametes within the testis through the coordination of mitotic, meiotic and differentiation events, under a deep control of endocrine, paracrine and autocrine modulators along the Hypothalamus-pituitary-gonad (HPG) axis. The kisspeptin system plays a fundamental role along the HPG axis as it is the main positive modulator upstream of the hypothalamic neurons that secrete the Gonadotropin Releasing Hormone (GnRH), the decapeptide that supports pituitary gonadotropins and the production of gonadal sex steroid. Currently, kisspeptins and their receptor, KISS1R, have a recognized activity in the central control of puberty onset, sex maturation, reproduction and sex-steroid feedback mechanisms in both animal models and human. However, kisspeptin signaling has been widely reported in peripheral tissues, particularly in the testis of mammalian and non-mammalian vertebrates, with functions related to Leydig cells physiology and steroid biosynthesis, spermatogenesis progression and spermatozoa functions, but its mandatory role within the testis is still a matter of discussion. This review provides a summary of the main intratesticular effects of kisspeptin in vertebrates, via a comparative approach. Particular emphasis was devoted to data from the anuran amphibian Pelophylax esculentus, the first animal model in which the direct intratesticular activity of kisspeptin was reported.

Environmental Impact on Male (In)Fertility via Epigenetic Route

In the last 40 years, male reproductive health-which is very sensitive to both environmental exposure and metabolic status-has deteriorated and the poor sperm quality observed has been suggested to affect offspring development and its health in adult life. In this scenario, evidence now suggests that epigenetics shapes endocrine functions, linking genetics and environment. During fertilization, spermatozoa share with the oocyte their epigenome, along with their haploid genome, in order to orchestrate embryo development. The epigenetic signature of spermatozoa is the result of a dynamic modulation of the epigenetic marks occurring, firstly, in the testis-during germ cell progression-then, along the epididymis, where spermatozoa still receive molecules, conveyed by epididymosomes. Paternal lifestyle, including nutrition and exposure to hazardous substances, alters the phenotype of the next generations, through the remodeling of a sperm epigenetic blueprint that dynamically reacts to a wide range of environmental and lifestyle stressors. With that in mind, this review will summarize and discuss insights into germline epigenetic plasticity caused by environmental stimuli and diet and how spermatozoa may be carriers of induced epimutations across generations through a mechanism known as paternal transgenerational epigenetic inheritance.

The Cannabinoid Receptor CB1 Stabilizes Sperm Chromatin Condensation Status During Epididymal Transit by Promoting Disulphide Bond Formation

The cannabinoid receptor CB1 regulates differentiation of spermatids. We recently characterized spermatozoa from caput epididymis of CB1-knock-out mice and identified a considerable number of sperm cells with chromatin abnormality such as elevated histone content and poorly condensed chromatin. In this paper, we extended our findings and studied the role of CB1 in the epididymal phase of chromatin condensation of spermatozoa by analysis of spermatozoa from caput and cauda epididymis of wild-type and CB1-knock-out mouse in both a homozygous or heterozygous condition. Furthermore, we studied the impact of CB1-gene deletion on histone displacement mechanism by taking into account the hyperacetylation of histone H4 and players of displacement such as Chromodomain Y Like protein (CDYL) and Bromodomain testis-specific protein (BRDT). Our results show that CB1, via local and/or endocrine cell-to-cell signaling, modulates chromatin remodeling mechanisms that orchestrate a nuclear condensation extent of mature spermatozoa. We show that CB1-gene deletion affects the epididymal phase of chromatin condensation by interfering with inter-/intra-protamine disulphide bridges formation, and deranges the efficiency of histone removal by reducing the hyper-acetylation of histone H4. This effect is independent by gene expression of Cdyl and Brdt mRNA. Our results reveal a novel and important role for CB1 in sperm chromatin condensation mechanisms.

CircRNA Role and circRNA-Dependent Network (ceRNET) in Asthenozoospermia

The role of circRNA in reproduction is under investigation. CircRNAs are expressed in human testis, spermatozoa (SPZ), and seminal plasma. Their involvement in embryo development has also been suggested. Asthenozoospermia, a common cause of male infertility, is characterized by reduced or absent sperm motility in fresh ejaculate. While abnormal mitochondrial function, altered sperm tail, and genomic causes have been deeply investigated, the epigenetic signature of asthenozoospermic derived SPZ still remains unexplored. CircRNAs may take part in the repertoire of differentially expressed molecules in infertile men. Considering this background, we carried out a circRNA microarray, identifying a total of 9,138 transcripts, 22% of them novel based and 83.5% with an exonic structure. Using KEGG analysis, we evaluated the circRNA contribution in pathways related to mitochondrial function and sperm motility. In order to discriminate circRNAs with a differential expression in SPZ with differential morphological parameters, we separated sperm cells by Percoll gradient and analyzed their differential circRNA payload. A bioinformatic approach was then utilized to build a circRNA/miRNA/mRNA network. With the aim to demonstrate a dynamic contribution of circRNAs to the sperm epigenetic signature, we verified their modulation as a consequence of an oral amino acid supplementation, efficacious in improving SPZ motility.