Alternative splicing and related RNA binding proteins in human health and disease

Alternative splicing (AS) serves as a pivotal mechanism in transcriptional regulation, engendering transcript diversity, and modifications in protein structure and functionality. Across varying tissues, developmental stages, or under specific conditions, AS gives rise to distinct splice isoforms. This implies that these isoforms possess unique temporal and spatial roles, thereby associating AS with standard biological activities and diseases. Among these, AS-related RNA-binding proteins (RBPs) play an instrumental role in regulating alternative splicing events. Under physiological conditions, the diversity of proteins mediated by AS influences the structure, function, interaction, and localization of proteins, thereby participating in the differentiation and development of an array of tissues and organs. Under pathological conditions, alterations in AS are linked with various diseases, particularly cancer. These changes can lead to modifications in gene splicing patterns, culminating in changes or loss of protein functionality. For instance, in cancer, abnormalities in AS and RBPs may result in aberrant expression of cancer-associated genes, thereby promoting the onset and progression of tumors. AS and RBPs are also associated with numerous neurodegenerative diseases and autoimmune diseases. Consequently, the study of AS across different tissues holds significant value. This review provides a detailed account of the recent advancements in the study of alternative splicing and AS-related RNA-binding proteins in tissue development and diseases, which aids in deepening the understanding of gene expression complexity and offers new insights and methodologies for precision medicine.

Cadmium-induced reproductive toxicity combined with a correlation to the oogenesis process and competing endogenous RNA networks based on a Caenorhabditis elegans model

Accumulation of the heavy metal Cadmium (Cd) in the ovaries and placenta can affect the structure and function of these organs and induce female reproductive toxicity. This toxicity may be due to Cd's similarity to estrogen and its ability to disrupt endocrine systems. However, the exact molecular mechanism by which Cd causes reproductive toxicity at the transcriptome level remains poorly understood. Hence, this study aimed to observe Cd-induced reproductive damage at the gene level, scrutinize the repercussions of Cd exposure on oogenesis, and explicate the putative pathogenesis of Cd-induced oogenesis based on Caenorhabditis elegans (C. elegans) as an in vivo model. The results showed that Cd exposure significantly decreased the number of offspring and prolonged the reproductive span of C. elegans. Cd exposure also reduced the number of cells in mitosis and the pachytene and diakinesis stages of meiosis, thereby disrupting oogenesis. Combined with transcriptional sequencing and bioinformatics analysis, a total of 3167 DEmRNAs were identified. Regarding gene expression, cul-6, mum-2, and vang-1 were found to be related to Cd-induced reproductive toxicity, and their competing endogenous RNA networks were constructed. We observed that mutations of mom-2 and vang-1 in the Wnt pathway could induce susceptibility to Cd-caused meiosis injury. In conclusion, the results indicated that Cd could impair the oogenesis of C. elegans and the Wnt pathway might serve as a protective mechanism against Cd reproductive toxicity. These findings contribute to a better understanding of the damaging effects and molecular biological mechanisms of Cd on the human reproductive system.

The Role of Circular RNAs in Male Infertility and Reproductive Cancers: A Narrative Review

Infertility is a global health problem affecting about 15% of all couples, of which 50% are due to male infertility. Although the etiology of infertility is known in most infertile men, idiopathic male infertility remains a challenge. Therefore, there is a need for novel diagnostic methods to detect the underlying mechanisms and develop appropriate therapies. Recent studies have focused on the role of non-coding RNAs (ncRNAs) in male infertility. Circular RNAs (CircRNAs), a type of ncRNAs, are found to play a key role in the development of some pathological conditions, including cardiovascular diseases, diabetes, cancers, autoimmune diseases, etc. Several studies have reported the presence of CircRNAs and their target genes in the human reproductive system. In addition, their expression in testicular tissues, sperm cells, and seminal fluid has been identified. Abnormal expression of CircRNAs has been associated with azoospermia and asthenozoospermia in infertile men. The present narrative review provides a brief description of the role of CircRNAs in spermatogenic cells, male infertility, and reproductive cancers. In addition, some CircRNAs have been identified as potential biomarkers for disease detection and treatment.

Retinoic acid-induced differentiation of porcine prospermatogonia in vitro

Spermatogenesis is an intricate developmental process occurring in testes by which spermatogonial stem cells (SSCs) self-renew and differentiate into mature sperm. The molecular mechanisms for SSC self-renewal and differentiation, while have been well studied in mice, may differ between mice and domestic animals including pigs. To gain knowledge about the molecular mechanisms for porcine SSC self-renewal and differentiation that have so far been poorly understood, here we isolated and enriched prospermatogonia from neonatal porcine testes, and exposed the cells to retinoic acid, a direct inducer for spermatogonial differentiation. We then identified that retinoic acid could induce porcine prospermatogonial differentiation, which was accompanied by a clear transcriptomic alteration, as revealed by the RNA-sequencing analysis. We also compared retinoic acid-induced in vitro porcine spermatogonial differentiation with the in vivo process, and compared retinoic acid-induced in vitro spermatogonial differentiation between pigs and mice. Furthermore, we analyzed retinoic acid-induced differentially expressed long non-coding RNAs (lncRNAs), and demonstrated that a pig-specific lncRNA, lncRNA-106504875, positively regulated porcine spermatogonial proliferation by targeting the core transcription factor ZBTB16. Taken together, these results would help to elucidate the roles of retinoic acid in porcine spermatogonial differentiation, thereby contributing to further knowledge about the molecular mechanisms underlying porcine SSC development and, in the long run, to optimization of both long-term culture and induced differentiation systems for porcine SSCs.

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.

Circular RNAs: Novel Biomarkers in Spermatogenesis Defects and Male Infertility

Circular RNAs (circRNAs) are a new class of endogenous non-coding RNAs involved in several cellular and biological processes, including gene expression regulation, microRNA function, transcription regulation, and translation modification. Therefore, these non-coding RNAs have important roles in the pathogenesis of various diseases. Male infertility is mainly due to abnormal sperm parameters such as motility, morphology, and concentration. Recent studies have confirmed the role of circRNAs in spermatogenesis, and the expression of several circRNAs is confirmed in seminal plasma, spermatozoa, and testicular tissue. It is suggested that deregulation of circRNAs is involved in different types of male infertility, including azoospermia, oligozoospermia, and asthenozoospermia. In the present review, we aimed to discuss the potential roles of circRNAs in spermatogenesis failure, sperm defects, and male infertility. Due to their conserved and special structure and tissue-specific expression pattern, circRNAs can be applied as reliable noninvasive molecular biomarkers, therapeutic and pharmaceutical targets in male infertility.

The molecular characteristics in different procedures of spermatogenesis

Spermatogenesis is a multistep biological process. In addition to somatic cells, it involves the orderly differentiation of dozens of spermatogenic cells. In this process, the regulatory networks between different spermatogenic cell populations are significantly different. RNA m6A regulators and miRNAs have been found to be closely related to spermatogenesis in recent years, and they are an important part of the above regulatory networks. Understanding gene expression and its rules in different spermatogenic cell populations will help in the in-depth exploration of their detailed roles in spermatogenesis. This study collected a public dataset of nonobstructive azoospermia (NOA). Based on the Johnson score, the testicular samples of NOA were divided into three types, Sertoli-cell only syndrome, meiotic arrest and postmeiotic arrest, which represented the loss of three germ cell populations, including whole spermatogenic cells, postmeiotic spermatogenic cells, and a mixture of late spermatids and spermatozoa, respectively. The aforementioned three types of testis data were compared with normal testis data, and the molecular expression characteristics of the abovementioned three germ cell populations were obtained. Our study showed that different germ cell populations have different active molecules and their pathways. In addition, RNA m6A regulators, including METTL3, IGF2BP2 and PRRC2A, and miRNAs, including hsa-let-7a-2, hsa-let-7f-1, hsa-let-7g, hsa-miR-15a, hsa-miR-197, hsa-miR-21, hsa-miR-30e, hsa-miR-32, hsa-miR-503 and hsa-miR-99a, also presented regulatory roles in almost all germ cells.

Integrative analysis of circRNAs from Yangtze River Delta white goat neck skin tissue by high-throughput sequencing (circRNA-seq)

The Yangtze River Delta white goat is a unique goat species that can produce superior-quality brush hair. The formation of this brush hair is controlled by a series of critical genes and related signaling pathways. Circular RNAs (circRNAs), are ubiquitous endogenous non-coding RNAs that regulate many biological and physiological processes in mammals. However, little is known about the potential regulatory role of circRNAs on superior-quality brush hair formation in Yangtze River Delta white goat. In this study, high-throughput sequencing technology was used to only detect circRNAs in the neck skin tissue of normal-quality goats (NHQs) and superior-quality goats (HQs). A total of 61 803 circRNAs were identified and 32 of them were differentially expressed in the NHQ group vs. the HQ group. Functional enrichment analysis showed that the source gene of differentially expressed circRNAs (DE-circRNAs) was enriched mostly in platelet activation and the focal adhesion signal pathway. Action mechanism analysis revealed that DE-circRNAs could sponge to many identified miRNAs, including miR-31, miR-125b, miR-let-7a and miR-149-5p, which have important roles in goat hair follicle stem cell growth, hair follicle development and morphogenesis. Altogether, our findings provide a valuable basis for studying circRNAs involved in superior-quality brush hair traits and meanwhile advance our understanding of circRNA complex regulation mechanisms in Yangtze River Delta white goat skin hair follicle development.

Circular RNAs in stem cells: from basic research to clinical implications

Circular RNAs (circRNAs) are a special class of endogenous RNAs with a wide variety of pathophysiological functions via diverse mechanisms, including transcription, microRNA (miRNA) sponge, protein sponge/decoy, and translation. Stem cells are pluripotent cells with unique properties of self-renewal and differentiation. Dysregulated circRNAs identified in various stem cell types can affect stem cell self-renewal and differentiation potential by manipulating stemness. However, the emerging roles of circRNAs in stem cells remain largely unknown. This review summarizes the major functions and mechanisms of action of circRNAs in stem cell biology and disease progression. We also highlight circRNA-mediated common pathways in diverse stem cell types and discuss their diagnostic significance with respect to stem cell-based therapy.

Photoperiods induced the circRNA differential expression in the thyroid gland of OVX+E2 ewes

Circular RNAs (circRNAs) are non-coding RNAs newly identified and play important roles in RNA regulation. However, little is known regarding photoperiods induced circRNAs in the thyroid gland. In this study, we performed a comprehensive analysis of circRNA profiles in the thyroid gland of OVX+E₂ ewes at different photoperiods by whole transcriptome sequencing. A total of 37,470 novel circRNAs were detected in different photoperiods (42 days of short photoperiod treatment, SP42; 42 days of long photoperiod treatment, LP42; SP42 transfer to LP42, SPLP42), with a total of 817 circRNAs for SP42-LP42 (down: 132; up: 114), LP42-SPLP42 (down: 136; up: 112) and SP42-SPLP42 (down: 182; up: 141) having differentially expressed. Functional enrichment annotation analysis of DE-circRNAs for GO and KEGG by R package, features that influence photoperiod response in Sunite ewes through the Inositol phosphate metabolism, cGMP-PKG signaling pathway, Calcium signaling pathway, MAPK signaling pathway, and Oocyte meiosis. In addition, competitive endogenous RNA (ceRNA) network analysis revealed target binding sites for identified miRNAs in DE-cirRNAs such as oar-miR-10b, oar-miR-200c, oar-miR-21, oar-miR-370-3p, oar-miR-377-3p, oar-miR-181a, oar-miR-432, and oar-miR-495-3p. These results of this study will provide some new information for understanding circRNA function as well as the changes in the sheep thyroid gland under different photoperiods.

Significance and Relevance of Spermatozoal RNAs to Male Fertility in Livestock

Livestock production contributes to a significant part of the economy in developing countries. Although artificial insemination techniques brought substantial improvements in reproductive efficiency, male infertility remains a leading challenge in livestock. Current strategies for the diagnosis of male infertility largely depend on the evaluation of semen parameters and fail to diagnose idiopathic infertility in most cases. Recent evidences show that spermatozoa contains a suit of RNA population whose profile differs between fertile and infertile males. Studies have also demonstrated the crucial roles of spermatozoal RNA (spRNA) in spermatogenesis, fertilization, and early embryonic development. Thus, the spRNA profile may serve as unique molecular signatures of fertile sperm and may play pivotal roles in the diagnosis and treatment of male fertility. This manuscript provides an update on various spRNA populations, including protein-coding and non-coding RNAs, in livestock species and their potential role in semen quality, particularly sperm motility, freezability, and fertility. The contribution of seminal plasma to the spRNA population is also discussed. Furthermore, we discussed the significance of rare non-coding RNAs (ncRNAs) such as long ncRNAs (lncRNAs) and circular RNAs (circRNAs) in spermatogenic events.

A systematic evaluation of the computational tools for lncRNA identification

The computational identification of long non-coding RNAs (lncRNAs) is important to study lncRNAs and their functions. Despite the existence of many computation tools for lncRNA identification, to our knowledge, there is no systematic evaluation of these tools on common datasets and no consensus regarding their performance and the importance of the features used. To fill this gap, in this study, we assessed the performance of 17 tools on several common datasets. We also investigated the importance of the features used by the tools. We found that the deep learning-based tools have the best performance in terms of identifying lncRNAs, and the peptide features do not contribute much to the tool accuracy. Moreover, when the transcripts in a cell type were considered, the performance of all tools significantly dropped, and the deep learning-based tools were no longer as good as other tools. Our study will serve as an excellent starting point for selecting tools and features for lncRNA identification.

The guardians of germ cells; Sertoli-derived exosomes against electromagnetic field-induced oxidative stress in mouse spermatogonial stem cells

Nowadays, prolonged exposure to electromagnetic fields (EMF) has raised public concern about the detrimental potential of EMF on spermatogonial stem cells (SSCs) and spermatogenesis. Recent studies introduced the fundamental role of Sertoli cell paracrine signaling in the regulation of SSCs maintenance and differentiation in fertility preservation. Thus we investigated the therapeutic effect of Sertoli-derived exosomes (Sertoli-EXOs) as powerful paracrine mediators in SSCs subjected to EMF and its underlying mechanisms. SSCs and Sertoli cells were isolated from neonate mice testis, and identified by their specific markers. Then SSCs were exposed to 50 Hz EMF with intensity of 2.5 mT (1 h for 5 days) and supplemented with exosomes that were isolated from pre-pubertal Sertoli cells. Sertoli-EXOs were characterized and the uptake was observed by PKH26 labeling. The cell viability, colonization efficiency, reactive oxygen species (ROS) balance, cell cycle arrest and apoptosis induction were then analysed. SSCs were confirmed by immunocytochemistry (Oct4, Plzf) and Sertoli cells were identified through Sox9 and vimentin expression by immunocytochemistry and Real-time PCR (qRT-PCR), respectively. Our results demonstrated the detrimental effect of EMF via ROS accumulation that reduced the expression of catalase antioxidant, cell viability and colonization of SSCs. Also, AO/PI and flow cytometry analysis demonstrated the elevation of apoptosis in SSCs exposed to EMF in comparison with control. qRT-PCR data confirmed the up-regulation of apoptotic gene (Caspase-3) and down-regulation of SSCs specific gene (GFRα1). Consequently, the administration of Sertoli-EXOs exerted ameliorative effect on SSCs and significantly improved these changes through the regulation of oxidative stress. These findings suggest that Sertoli-EXOs have positive impact on SSCs exposed to EMF and can be useful in further investigation of Sertoli-EXOs as a novel therapeutic agent which may recover the deregulated SSCs microenvironment and spermatogenesis after exposure to EMF.

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.

Environmental pollutants exposure and male reproductive toxicity: The role of epigenetic modifications

Male fertility rates have shown a progressive decrease in recent decades. There is a growing concern about the male reproductive dysfunction caused by environmental pollutants exposure, however the underlying molecular mechanisms are still not well understood. Epigenetic modifications play a key role in the biological responses to external stressors. Therefore, this review discusses the roles of epigenetic modifications in male reproductive toxicity induced by environmental pollutants, with a particular emphasis on DNA methylation, histone modifications and miRNAs. The available literature proposed that environmental pollutants can directly or cause oxidative stress and DNA damage to induce a variety of epigenetic changes, which lead to gene dysregulation, mitochondrial dysfunction and consequent male reproductive toxicity. However, future studies focusing on more kinds of epigenetic modifications and their crosstalk as well as epidemiological data are still required to fill in the current research gaps. In addition, the intrinsic links between pollutants-mediated epigenetic regulations and male reproduction-related physiological responses deserve to be further explored.

Unraveling Stage-Dependent Expression Patterns of Circular RNAs and Their Related ceRNA Modulation in Ovine Postnatal Testis Development

Circular RNAs (circRNAs) have been shown to function in the reproductive systems including testis. However, their expression, as well as function in testicular development of sheep remain undefined. Herein, we performed RNA sequencing to reveal circRNA temporal expression patterns in testes of Tibetan sheep from different stages of maturation (3M, 3-month-old; 1Y, 1-year-old; 3Y, 3-year-old). A total of 3,982, 414, and 4,060 differentially expressed (DE) circRNAs were uncovered from 3M vs 1Y, 1Y vs 3Y, and 3M vs 3Y, respectively. Functional enrichment assessment indicated that the source genes of DE circRNAs were primarily engaged in spermatogenesis and testicular immune privilege including blood-testis barrier (BTB). We subsequently constructed the core circRNA-miRNA-mRNA interaction network for genes related to testicular function, such as spermatogenesis, germ cell development, BTB, and cell cycle/meiosis. Furthermore, we validated the target associations between either circ_024949, circ_026259 or IGF1, and oar-miR-29b in this network, and revealed their similar expression signatures in developmental testes that they were extensively expressed in germ cells, Leydig cells, and Sertoli cells, thus suggesting their broad functions in the functional maintenance of Leydig cells and Sertoli cells, as well as the development and maturation of male germ cells. Meanwhile, circ_026259 was shown to promote IGF1 expression through inhibition of oar-miR-29b in sheep Sertoli cells. This work gives the first global view for the expression and regulation of circRNAs in sheep testis, which will be helpful for providing new insights into the molecular mechanism of ovine testis function.

EH domain binding protein 1-like 1 (EHBP1L1), a protein with calponin homology domain, is expressed in the rat testis

In this paper, with the aim to find new genes involved in mammalian spermatogenesis, we isolated, for the first time in the rat testis, a partial cDNA clone that encoded EH domain binding protein 1-like 1 (Ehbp1l1), a protein that has a single calponin homology domain (CH). Bioinformatic analysis showed that EHBP1l1 contains three domains: the N-terminal C2-like, the CH and the C-terminal bivalent Mical/EHBP Rab binding (bMERB) domains, which are evolutionarily conserved in vertebrates. We found that Ehbp1l1 mRNA was expressed in several rat tissues, including the liver, intestine, kidney and also in the testis during its development, with a higher level in testis from 12-month-old animals. Interestingly, in situ hybridization experiments revealed that Ehbp1l1 is specifically expressed by types I and II spermatocytes, this result was validated by RT-PCR performed on total RNA obtained from enriched fractions of different testicular cell types. As EHBP1l1 has been described as linked to vesicular transport to the actin cytoskeleton and as an effector of the small GTPase Rab8, we hypothesized that it could participate both in cytoskeletal remodelling and in the regulation of vesicle sorting from the trans-Golgi network to the apical plasma membrane. Our findings provide a better understand of the molecular mechanisms of the differentiation process of spermatogenesis; Ehbp1l1 may also be used as a new marker of testicular activity.

Investigating the regulatory function of the ANO1-AS2 on the ANO1 gene in infertile men with asthenozoospermia and terato-asthenozoospermia

Long non-coding RNAs (lncRNAs) have a particular expression in the testicular tissue and exhibit a regulatory function on the reproduction system. ANO1-AS2 (linc02584), as an lncRNA is located near the anoctamin1 (ANO1) gene. ANO1 is an important component of the transmembrane system exhibiting expression modifications in the idiopathic infertile men. Therefore, the present study was conducted to investigate the relationship between ANO1-AS2 and ANO1 gene expression with sperm motility and morphology in the patients with asthenozoospermia (AZ) and terato- asthenozoospermia (TAZ). The study population included 32 patients with AZ, 35 patients with TAZ, and 34 people with normozoospermia (NZ, control). The expression levels of ANO1 gene and ANO1-AS2 in the spermatozoa were measured by the quantitative real-time polymerase chain reaction (PCR). Docking analysis was performed to investigate the interactions of the ANO1 gene promoter and intermediate elements with ANO1-AS2. ANO1 gene expression was significantly (P < 0.05) downregulated in the patients however; ANO1-AS2 expression was significantly upregulated (P < 0.05). The subsequent analysis confirmed the inverse correlation between ANO1 and ANO1-AS2. ANO1 gene expression level was significantly positively correlated with sperm motility and morphology (P < 0.05). Moreover, ANO1-AS2 expression showed an inverse correlation with sperm motility and morphology (P < 0.05). Docking analysis confirmed that ANO1-AS2 could stably interact with ANO1 gene promoter. In conclusion, ANO1-AS2 is likely to downregulate the ANO1 gene by interacting with ANO1 gene promoter, which can influence the sperm motility and morphology.

Cdc14a has a role in spermatogenesis, sperm maturation and male fertility

Cdc14a is an evolutionarily conserved dual-specific protein phosphatase, and it plays different roles in different organisms. Cdc14a mutations in human have been reported to cause male infertility, while the specific role of Cdc14a in regulation of the male reproductive system remains elusive. In the present study, we established a knockout mouse model to study the function of Cdc14a in male reproductive system. Cdc14a^-/- male mice were subfertile and they could only produce very few offspring. The number of sperm was decreased, the sperm motility was impaired, and the proportion of sperm with abnormal morphology was elevated in Cdc14a^-/- mice. When we mated Cdc14a^-/- male mice with wild-type (WT) female mice, fertilized eggs could be found in female fallopian tubes, however, the majority of these embryos died during development. Some empty spaces were observed in seminiferous tubule of Cdc14a^-/- testes. Compared with WT male mice, the proportions of pachytene spermatocytes were increased and germ cells stained with γH2ax were decreased in Cdc14a^-/- male mice, indicating that knockout of Cdc14a inhibited meiotic initiation. Subsequently, we analyzed the expression levels of some substrate proteins of Cdc14a, including Cdc25a, Wee1, and PR-Set7, and compared those with WT testes, in which the expression levels of these proteins were significantly increased in Cdc14a^-/- testes. Our results revealed that Cdc14a^-/- male mice are highly subfertile, and Cdc14a is essential for normal spermatogenesis and sperm function.

Circular RNAs in Embryogenesis and Cell Differentiation With a Focus on Cancer Development

In the recent years thousands of non-coding RNAs have been identified, also thanks to highthroughput sequencing technologies. Among them, circular RNAs (circRNAs) are a well-represented class characterized by the high sequence conservation and cell type specific expression in eukaryotes. They are covalently closed loops formed through back-splicing. Recently, circRNAs were shown to regulate a variety of cellular processes functioning as miRNA sponges, RBP binding molecules, transcriptional regulators, scaffold for protein translation, as well as immune regulators. A growing number of studies are showing that deregulated expression of circRNAs plays important and decisive actions during the development of several human diseases, including cancer. The research on their biogenesis and on the various molecular mechanisms in which they are involved is going very fast, however, there are still few studies that address their involvement in embryogenesis and eukaryotic development. This review has the intent to describe the most recent progress in the study of the biogenesis and molecular activities of circRNAs providing insightful information in the field of embryogenesis and cell differentiation. In addition, we describe the latest research on circRNAs as novel promising biomarkers in diverse types of tumors.

Comprehensive Analysis of Differentially Expressed Profiles of mRNA, lncRNA, and circRNA in the Uterus of Seasonal Reproduction Sheep

Photoperiod is one of the important factors leading to seasonal reproduction of sheep. However, the molecular mechanisms underlying the photoperiod regulation of seasonal reproduction remain poorly understood. In this study, we compared the expression profiles of mRNAs, lncRNAs, and circRNAs in uterine tissues from Sunite sheep during three different photoperiods, namely, the short photoperiod (SP), short transfer to long photoperiod (SLP), and long photoperiod (LP). The results showed that 298, 403, and 378 differentially expressed (DE) mRNAs, 171, 491, and 499 DE lncRNAs, and 124, 270, and 400 DE circRNAs were identified between SP and LP, between SP and SLP, and between LP and SLP, respectively. Furthermore, functional enrichment analysis showed that the differentially expressed RNAs were mainly involved in the GnRH signaling pathway, thyroid hormone synthesis, and thyroid hormone signaling pathway. In addition, co-expression networks of lncRNA–mRNA were constructed based on the correlation analysis between the differentially expressed RNAs. Our study provides new insights into the expression changes of RNAs in different photoperiods, which might contribute to understanding the molecular mechanisms of seasonal reproduction in sheep.

RNA: interactions drive functionalities

RNA is produced from the majority of human genomic sequences, although only a relatively small portion of these transcripts has known functions. Diverse RNA species interact with RNA, DNA, proteins, lipids, and metabolites to form intricate molecular networks. In this review, we attempt to delineate diverse RNA functions by interaction types between RNA and other macromolecules. Through such interactions RNAs participate in essentially every major molecular function and process, including information flow and storage, environment sensing, signal transduction, and gene regulation at transcriptional and posttranscriptional levels. Through such interactions, RNAs promote or inhibit diverse biological processes, and act as catalyzer or quencher to modulate the pace of these progresses. Alterations and personal variations of these interactions are mechanistically coupled with disease etiology and phenotypical variations for clinical use.

The Function of Pre-mRNA Alternative Splicing in Mammal Spermatogenesis

Alternative pre-mRNA splicing plays important roles in co-transcriptional and post-transcriptional regulation of gene expression functioned during many developmental processes, such as spermatogenesis. The studies focusing on alternative splicing on spermatogenesis supported the notion that the development of testis is regulated by a higher level of alternative splicing than other tissues. Here, we aim to review the mechanisms underlying alternative splicing, particularly the splicing variants functioned in the process of spermatogenesis and the male infertility. There are five points regarding the alternative splicing including ⅰ) a brief introduction of alternative pre-mRNA splicing; ⅱ) the alternative splicing events in spermatogenesis-associated genes enriched in different stages of spermatogenesis; ⅲ) the mechanisms of alternative splicing regulation, such as splicing factors and m⁶A demethylation; ⅳ) the splice site recognition and alternative splicing, including the production and degradation of abnormal transcripts caused by gene variations and nonsense-mediated mRNA decay, respectively; ⅴ) abnormal alternative splicing correlated with male infertility. Taking together, this review highlights the impacts of alternative splicing and splicing variants in mammal spermatogenesis and provides new insights of the potential application of the alternative splicing into the therapy of male infertility.