RNA in human sperm

The ribosome inhibitor chloramphenicol induces motility deficits in human spermatozoa: A proteomic approach identifies potentially involved proteins

Mature spermatozoa are almost completely devoid of cytoplasm; as such it has long been believed that they do not contain ribosomes and are therefore not capable of synthesising proteins. However, since the 1950s, various studies have shown translational activity within spermatozoa, particularly during their in vitro capacitation. But the type of ribosomes involved (cytoplasmic or mitochondrial) is still debated. Here, we investigate the presence and activity of the two types of ribosomes in mature human spermatozoa. By targeting ribosomal RNAs and proteins, we show that both types of ribosomes are localized in the midpiece as well as in the neck and the base of the head of the spermatozoa. We assessed the impact of cycloheximide (CHX) and chloramphenicol (CP), inhibitors of cytoplasmic and mitochondrial ribosomes, respectively, on different sperm parameters. Neither CHX, nor CP impacted sperm vitality, mitochondrial activity (measured through the ATP content), or capacitation (measured through the content in phosphotyrosines). However, increasing CP concentrations induced a decrease in total and progressive motilities as well as on some kinematic parameters while no effect was observed with CHX. A quantitative proteomic analysis was performed by mass spectrometry in SWATH mode to compare the proteomes of spermatozoa capacitated in the absence or presence of the two ribosome inhibitors. Among the ∼700 proteins identified in the different tested conditions, 3, 3 and 25 proteins presented a modified abundance in the presence of 1 and 2 mg/ml of CHX, and 1 mg/ml of CP, respectively. The observed abundance variations of some CP-down regulated proteins were validated using Multiple-Reaction Monitoring (MRM). Taken together, our results are in favor of an activity of mitochondrial ribosomes. Their inhibition by CP results in a decrease in the abundance of several proteins, at least FUNDC2 and QRICH2, and consequently induces sperm motility deficits.

Perinatal Exposure to Nicotine Alters Sperm RNA Profiles in Rats

Perinatal exposure to smoking has been associated with childhood asthma, one of the most common pediatric conditions affecting millions of children globally. Of great interest, this disease phenotype appears heritable as it can persist across multiple generations even in the absence of persistent exposure to smoking in subsequent generations. Although the molecular mechanisms underlying childhood asthma induced by perinatal exposure to smoking or nicotine remain elusive, an epigenetic mechanism has been proposed, which is supported by the data from our earlier analyses on germline DNA methylation (5mC) and histone marks (H3 and H4 acetylation). To further investigate the potential epigenetic inheritance of childhood asthma induced by perinatal nicotine exposure, we profiled both large and small RNAs in the sperm of F1 male rats. Our data revealed that perinatal exposure to nicotine leads to alterations in the profiles of sperm-borne RNAs, including mRNAs and small RNAs, and that rosiglitazone, a PPARγ agonist, can attenuate the effect of nicotine and reverse the sperm-borne RNA profiles of F1 male rats to close to placebo control levels.

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.

Single-molecule long-read sequencing reveals a conserved intact long RNA profile in sperm

Sperm contributes diverse RNAs to the zygote. While sperm small RNAs have been shown to impact offspring phenotypes, our knowledge of the sperm transcriptome, especially the composition of long RNAs, has been limited by the lack of sensitive, high-throughput experimental techniques that can distinguish intact RNAs from fragmented RNAs, known to abound in sperm. Here, we integrate single-molecule long-read sequencing with short-read sequencing to detect sperm intact RNAs (spiRNAs). We identify 3440 spiRNA species in mice and 4100 in humans. The spiRNA profile consists of both mRNAs and long non-coding RNAs, is evolutionarily conserved between mice and humans, and displays an enrichment in mRNAs encoding for ribosome. In sum, we characterize the landscape of intact long RNAs in sperm, paving the way for future studies on their biogenesis and functions. Our experimental and bioinformatics approaches can be applied to other tissues and organisms to detect intact transcripts.

Paternal impacts on development: identification of genomic regions vulnerable to oxidative DNA damage in human spermatozoa

STUDY QUESTION

Do all regions of the paternal genome within the gamete display equivalent vulnerability to oxidative DNA damage?

SUMMARY ANSWER

Oxidative DNA damage is not randomly distributed in mature human spermatozoa but is instead targeted, with particular chromosomes being especially vulnerable to oxidative stress.

WHAT IS KNOWN ALREADY

Oxidative DNA damage is frequently encountered in the spermatozoa of male infertility patients. Such lesions can influence the incidence of de novo mutations in children, yet it remains to be established whether all regions of the sperm genome display equivalent susceptibility to attack by reactive oxygen species.

STUDY DESIGN, SIZE, DURATION

Human spermatozoa obtained from normozoospermic males (n = 8) were split into equivalent samples and subjected to either hydrogen peroxide (H2O2) treatment or vehicle controls before extraction of oxidized DNA using a modified DNA immunoprecipitation (MoDIP) protocol. Specific regions of the genome susceptible to oxidative damage were identified by next-generation sequencing and validated in the spermatozoa of normozoospermic males (n = 18) and in patients undergoing infertility evaluation (n = 14).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Human spermatozoa were obtained from normozoospermic males and divided into two identical samples prior to being incubated with either H2O2 (5 mm, 1 h) to elicit oxidative stress or an equal volume of vehicle (untreated controls). Alternatively, spermatozoa were obtained from fertility patients assessed as having high basal levels of oxidative stress within their spermatozoa. All semen samples were subjected to MoDIP to selectively isolate oxidized DNA, prior to sequencing of the resultant DNA fragments using a next-generation whole-genomic sequencing platform. Bioinformatic analysis was then employed to identify genomic regions vulnerable to oxidative damage, several of which were selected for real-time quantitative PCR (qPCR) validation.

MAIN RESULTS AND THE ROLE OF CHANCE

Approximately 9000 genomic regions, 150–1000 bp in size, were identified as highly vulnerable to oxidative damage in human spermatozoa. Specific chromosomes showed differential susceptibility to damage, with chromosome 15 being particularly sensitive to oxidative attack while the sex chromosomes were protected. Susceptible regions generally lay outside protamine- and histone-packaged domains. Furthermore, we confirmed that these susceptible genomic sites experienced a dramatic (2–15-fold) increase in their burden of oxidative DNA damage in patients undergoing infertility evaluation compared to normal healthy donors.

LIMITATIONS, REASONS FOR CAUTION

The limited number of samples analysed in this study warrants external validation, as do the implications of our findings. Selection of male fertility patients was based on high basal levels of oxidative stress within their spermatozoa as opposed to specific sub-classes of male factor infertility.

WIDER IMPLICATIONS OF THE FINDINGS

The identification of genomic regions susceptible to oxidation in the male germ line will be of value in focusing future analyses into the mutational load carried by children in response to paternal factors such as age, the treatment of male infertility using ART and paternal exposure to environmental toxicants.

STUDY FUNDING/COMPETING INTEREST(S)

Project support was provided by the University of Newcastle’s (UoN) Priority Research Centre for Reproductive Science. M.J.X. was a recipient of a UoN International Postgraduate Research Scholarship. B.N. is the recipient of a National Health and Medical Research Council of Australia Senior Research Fellowship. Authors declare no conflict of interest.

Implication of transcriptome profiling of spermatozoa for stallion fertility

Poor fertility of breeding stallions is a recognised problem in the equine industry. The aim of the present study was to detect molecular pathways using two groups of stallions that differed in pregnancy rates as well as in the proportion of normal and motile spermatozoa. RNA was isolated from spermatozoa of each stallion and microarray data were analysed to obtain a list of genes for which transcript abundance differed between the groups (P ≤0.05, fold change ≥1.2). In all, there were 437 differentially expressed (DE) genes between the two groups (P ≤ 0.05, fold change ≥1.2). Next, the DE genes were analysed using Database for Annotation, Visualisation, and Integrated Discovery (DAVID). Finally, ingenuity pathways analysis (IPA) was used to identify top biological functions and significant canonical pathways associated with the DE genes. Analysis using the DAVID database showed significant enrichment in the gene ontology (GO) term 'RNA binding' (P=0.05) and in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway cytokine-cytokine receptor interaction (P=0.02). Furthermore, IPA analysis showed interconnected biological functions and canonical pathways involved in the regulation of spermatogenesis and male fertility. In addition, significantly enriched metabolic pathways were identified. In conclusion, the present study has identified, for the first time, molecular processes in stallion spermatozoa that could be associated with stallion fertility.

Epigenetics, infertility, and cancer: future directions

Although direct correlates between cancer and infertile epigenetic profiles are rare, the general similarities between the two disease processes offer insights into the study of both abnormalities. Foremost among them is the nature of these pathologies, where one disease (cancer) is categorized by an inability to control or inhibit cellular proliferation, and the other (male infertility) is caused by an inability to maintain the normally efficient extreme proliferation of the male germ cell. Based on this similarity alone, the study of epigenetics in both male fertility and cancer has the potential to offer intriguing insights in both fields. The creative application of harmonious studies of both infertility and cancer is likely to yield useful and informative data that may aid in both the understanding and treatment of both pathologies.

Molecular study of human sperm RNA: Ropporin and CABYR in asthenozoospermia

BACKGROUND

Sperm motility is an essential aspect of human fertility. Sperm contain an abundance of transcripts, thought to be remnants of mRNA, which comprise a genetic fingerprint and can be considered a historic record of gene expression during spermatogenesis. The aberrant expression of numerous genes has been found to contribute to impaired sperm motility; these include ROPN1 (rhophilin associated tail protein 1), which encodes a component of the fibrous sheath of the mammalian sperm flagella, and CABYR (calcium-binding tyrosine-(Y)-phosphorylation-regulated protein), which plays an important role in calcium activation and modulation. The aim of this study was to investigate ROPN1 and CABYR gene co-expression in asthenozoospermic semen samples in comparison with normozoospermic samples.

METHODS

We studied 120 semen samples (60 normozoospermic and 60 asthenozoospermic) from Caucasian patients attending our centre for an andrological check-up. Total RNA was extracted from purified spermatozoa with RNeasy mini kit. ROPN1 and CABYR mRNA expression was analysed using RT-qPCR. Continuous variables were described as means ± standard deviations.

RESULTS

ROPN1 and CABYR mRNA were simultaneously downregulated in asthenozoospermic in comparison with normozoospermic samples. There was also a positive correlation between total progressive motility and ROPN1 and CABYR gene expression and between total motile sperm number and ROPN1 and CABYR gene expression.

CONCLUSIONS

The results demonstrated downregulation of both ROPN1 and CABYR in asthenozoospermic samples and importantly, a positive correlation between the expression of the two genes, suggesting that ROPN1 and CABYR co-expression is a prerequisite for normal flagellar function and sperm motility.

The bovine sex-determining region Y (Sry) gene and its mRNA transcript are present in Y sperm but not X sperm of bulls

The aims of this study were to establish whether the sex-determining region Y gene and its mRNA transcript are present in the Y sperm and X sperm of bulls and, if present, determine their cellular localization. Semen was collected from three bulls and sorted by flow cytometry into X- and Y-chromosome populations. Reverse transcription-polymerase chain reaction (RT-PCR) was used to determine Sry mRNA expression in X sperm and Y sperm. The presence and localization of Sry DNA and RNA were investigated by fluorescence in situ hybridization (FISH). RT-PCR detected a single Sry transcript of 142 bp in Y sperm but not in X sperm. In Y sperm, the FISH-positive rates for Sry DNA and Sry RNA did not differ significantly from the re-analyzed Y sperm purity. In further experiments, there were no significant differences between the FISH-positive rate for Sry RNA and the re-analyzed Y sperm purity for X-sorted, Y-sorted, or unsorted sperm. In conclusion, FISH analysis revealed that Sry transcripts are present at the edges of the sperm heads of Y sperm but are absent from X sperm.

Analysis of the small non-protein-coding RNA profile of mouse spermatozoa reveals specific enrichment of piRNAs within mature spermatozoa

Post-testicular sperm maturation and storage within the epididymis is a key determinant of gamete quality and fertilization competence. Here we demonstrate that mouse spermatozoa possess a complex small non-protein-coding RNA (sRNA) profile, the composition of which is markedly influenced by their epididymal transit. Thus, although microRNAs (miRNAs) are highly represented in the spermatozoa of the proximal epididymis, this sRNA class is largely diminished in mature spermatozoa of the distal epididymis. Coincident with this, a substantial enrichment in Piwi-interacting RNA (piRNA) abundance in cauda spermatozoa was detected. Further, features of cauda piRNAs, including; predominantly 29-31 nts in length; preference for uracil at their 5' terminus; no adenine enrichment at piRNA nt 10, and; predominantly mapping to intergenic regions of the mouse genome, indicate that these piRNAs are generated by the PIWIL1-directed primary piRNA production pathway. Accordingly, PIWIL1 was detected via immunoblotting and mass spectrometry in epididymal spermatozoa. These data provide insight into the complexity and dynamic nature of the sRNA profile of spermatozoa and raise the intriguing prospect that piRNAs are generated in situ in maturing spermatozoa. Such information is of particular interest in view of the potential role for paternal sRNAs in influencing conception, embryo development and intergenerational inheritance.

Evaluation of spermatozoal function-useful tools or just science

Conventional microscopic semen analysis does not provide precise information on the fertilizing potential of a male. The traditional basis for semen evaluation is that male fertility is dependent on production of a "proper" concentration/number of motile, morphologically normal spermatozoa in excess to achieve conception. Many independent studies, especially in human medicine, have demonstrated that the absolute number of spermatozoa does not accurately determine fertility, but their functional competence. Many functional tests of spermatozoa are developed over the last decades. Computer-assisted sperm analysis (CASA) and flow cytometry have become the gold standard for semen assessment in specialized andrology laboratories. Other functional assays, such as gamete interaction tests, provide additional information regarding the real fertilizing potential of sperm cells. From this point of view, such tests are valuable diagnostic tools in fertility disorders and may be helpful to make a decision which method of treatment to use: pharmacological therapy, intrauterine insemination, introduction of classic IVF, ICSI or exclusion from a breeding programme. The most useful gamete interaction tests include induced acrosome reaction, zona pellucida binding assay, oocyte penetration assay and hyaluronan binding assay. In recent years, andrology has entered into a new era of sophisticated OMICS methods. Genomics, epigenomics, transcriptomics and proteomics brought high hopes for rapid progress in clinical diagnostics.

The small RNA content of human sperm reveals pseudogene-derived piRNAs complementary to protein-coding genes

At the end of mammalian sperm development, sperm cells expel most of their cytoplasm and dispose of the majority of their RNA. Yet, hundreds of RNA molecules remain in mature sperm. The biological significance of the vast majority of these molecules is unclear. To better understand the processes that generate sperm small RNAs and what roles they may have, we sequenced and characterized the small RNA content of sperm samples from two human fertile individuals. We detected 182 microRNAs, some of which are highly abundant. The most abundant microRNA in sperm is miR-1246 with predicted targets among sperm-specific genes. The most abundant class of small noncoding RNAs in sperm are PIWI-interacting RNAs (piRNAs). Surprisingly, we found that human sperm cells contain piRNAs processed from pseudogenes. Clusters of piRNAs from human testes contain pseudogenes transcribed in the antisense strand and processed into small RNAs. Several human protein-coding genes contain antisense predicted targets of pseudogene-derived piRNAs in the male germline and these piRNAs are still found in mature sperm. Our study provides the most extensive data set and annotation of human sperm small RNAs to date and is a resource for further functional studies on the roles of sperm small RNAs. In addition, we propose that some of the pseudogene-derived human piRNAs may regulate expression of their parent gene in the male germline.

Expression of miRNAs in Bull Spermatozoa Correlates with Fertility Rates

Bull spermatozoa are rich in active miRNAs, and it has been shown that specific spermborne miRNAs can be linked to fertility. Thus, expression profiling of spermatozoa could be helpful for understanding male fertility and the ability of spermatozoa to initiate and sustain zygotic, embryonic and foetal development. Herein we hypothesized that bulls with moderate to high fertility can be identified by differences in amounts of certain miRNAs between their ejaculates. RNA samples from spermatozoa of eight brother pairs (one bull with high and one with moderate NRR in each pair) of the Holstein breed were prepared. miRNA was isolated, and the expression of 178 miRNAs was determined by RT-qPCR. Important findings were that highly expressed miRNAs, not linked to NRR status, were identified in the bull sperm samples, which indicate that these miRNAs have an important role in early embryogenesis. A large fraction of the targets genes were phosphoproteins and genes involved in the regulation of transcription. Seven miRNAs (mir-502-5p, mir-1249, mir-320a, mir-34c-3p, mir-19b-3p, mir-27a-5p and mir-148b-3p) were differentially expressed between bulls with moderate and high NRR with a strong tendency towards a higher expression of miRNAs in bulls with moderate fertility. Thus, bulls with a moderate NRR negatively regulate the expression of protein-coding genes, which leads to problems during the pregnancy.

Differential Genes Expression between Fertile and Infertile Spermatozoa Revealed by Transcriptome Analysis

Background

It was believed earlier that spermatozoa have no traces of RNA because of loss of most of the cytoplasm. Recent studies have revealed the presence of about 3000 different kinds of mRNAs in ejaculated spermatozoa. However, the correlation of transcriptome profile with infertility remains obscure.

Methods

Total RNA from sperm (after exclusion of somatic cells) of 60 men consisting of individuals with known fertility (n=20), idiopathic infertility (normozoospermic patients, n=20), and asthenozoospermia (n=20) was isolated. After RNA quality check on Bioanalyzer, AffymetrixGeneChip Human Gene 1.0 ST Array was used for expression profiling, which consisted of >30,000 coding transcripts and >11,000 long intergenic non-coding transcripts.

Results

Comparison between all three groups revealed that two thousand and eighty one transcripts were differentially expressed. Analysis of these transcripts showed that some transcripts [ribosomal proteins (RPS25, RPS11, RPS13, RPL30, RPL34, RPL27, RPS5), HINT1, HSP90AB1, SRSF9, EIF4G2, ILF2] were up-regulated in the normozoospermic group, but down-regulated in the asthenozoospermic group in comparison to the control group. Some transcripts were specific to the normozoospermic group (up-regulated: CAPNS1, FAM153C, ARF1, CFL1, RPL19, USP22; down-regulated: ZNF90, SMNDC1, c14orf126, HNRNPK), while some were specific to the asthenozoospermic group (up-regulated: RPL24, HNRNPM, RPL4, PRPF8, HTN3, RPL11, RPL28, RPS16, SLC25A3, C2orf24, RHOA, GDI2, NONO, PARK7; down-regulated: HNRNPC, SMARCAD1, RPS24, RPS24, RPS27A, KIFAP3). A number of differentially expressed transcripts in spermatozoa were related to reproduction (n = 58) and development (n= 210). Some of these transcripts were related to heat shock proteins (DNAJB4, DNAJB14), testis specific genes (TCP11, TESK1, TSPYL1, ADAD1), and Y-chromosome genes (DAZ1, TSPYL1).

Conclusion

A complex RNA population in spermatozoa consisted of coding and non-coding RNAs. A number of transcripts that participate in a host of cellular processes, including reproduction and development were differentially expressed between fertile and infertile individuals. Differences between comparison groups suggest that sperm RNA has strong potential of acting as markers for fertility evaluation.

mir-34b/c and mir-449a/b/c are required for spermatogenesis, but not for the first cleavage division in mice

Mammalian sperm are carriers of not only the paternal genome, but also the paternal epigenome in the forms of DNA methylation, retained histones and noncoding RNAs. Although paternal DNA methylation and histone retention sites have been correlated with protein-coding genes that are critical for preimplantation embryonic development, physiological evidence of an essential role of these epigenetic marks in fertilization and early development remains lacking. Two miRNA clusters consisting of five miRNAs (miR-34b/c and miR-449a/b/c) are present in sperm, but absent in oocytes, and miR-34c has been reported to be essential for the first cleavage division in vitro. Here, we show that both miR-34b/c- and miR-449-null male mice displayed normal fertility, and that intracytoplasmic injection of either miR-34b/c- or miR-449-null sperm led to normal fertilization, normal preimplantation development and normal birth rate. However, miR-34b/c and miR-449 double knockout (miR-dKO) males were infertile due to severe spermatogenic disruptions and oligo-astheno-teratozoospermia. Injection of miR-dKO sperm into wild-type oocytes led to a block at the two-pronucleus to zygote transition, whereas normal preimplantation development and healthy pups were obtained through injection of miR-dKO round spermatids. Our data demonstrate that miR-34b/c and miR-449a/b/c are essential for normal spermatogenesis and male fertility, but their presence in sperm is dispensable for fertilization and preimplantation development.

Potential roles of noncoding RNAs in environmental epigenetic transgenerational inheritance

"Epigenetic transgenerational inheritance" (ETI) has been defined as germline (sperm or egg) transmission of epigenetic information between generations in the absence of direct exposures or genetic manipulations. Among reported cases of ETI in mammals, the majority are induced by environmental factors, including environmental toxicants [e.g. agricultural fungicide vinclozolin, plastic additive bisphenol A, pesticide methoxychlor, dioxin, di-(2-ethylhexyl) phthalate, dichlorodiphenyltrichloroethane, and hydrocarbons] and poor nutritional conditions. Although the ETI phenomenon is well established, the underlying mechanism remains elusive. Putative epimutations, including changes in DNA methylation and histone modification patterns, have been reported, but it remains unclear how these epimutations are formed in the first place, and how they are memorized in the germline and then get transmitted to subsequent generations. Based on recent advances in our understanding of regulatory noncoding RNAs (ncRNAs), I propose that ncRNAs are involved in ETI, during both the initial epimutation formation and the subsequent germline transmission of epimutations. ncRNAs can function at epigenetic levels by affecting DNA methylation and histone modifications, thereby changing gene transcriptional activities, which can lead to an altered mRNA transcriptome associated with a disease phenotype. Alternatively, novel or altered ncRNA expression can cause dysregulated post-transcriptional regulation, thus directly affecting the mRNA transcriptome and inducing a disease phenotype. Sperm-borne ncRNAs are potential mediators for epigenetic memory across generations, but they alone may not be sufficient for stable transmission of epimutations across generations. Overall, research on ncRNAs in the context of ETI is urgently needed to shed light on the underlying mechanism of ETI.

OMICS: Current and future perspectives in reproductive medicine and technology

Many couples present fertility problems at their reproductive age, and although in the last years, the efficiency of assisted reproduction techniques has increased, these are still far from being 100% effective. A key issue in this field is the proper assessment of germ cells, embryos and endometrium quality, in order to determine the actual likelihood to succeed. Currently available analysis is mainly based on morphological features of oocytes, sperm and embryos and although these strategies have improved the results, there is an urgent need of new diagnostic and therapeutic tools. The emergence of the - OMICS technologies (epigenomics, genomics, transcriptomics, proteomics and metabolomics) permitted the improvement on the knowledge in this field, by providing with a huge amount of information regarding the biological processes involved in reproductive success, thereby getting a broader view of complex biological systems with a relatively low cost and effort.

Genome-wide microarray analysis of Atlantic cod (Gadus morhua) oocyte and embryo

Background

Regulation of gene expression plays a central role in embryonic development. Early stages are controlled by gametic transcripts, which are subsequently substituted with transcripts from the genome of the zygote. Transcriptomic analyses provide an efficient approach to explore the temporal gene expression profiles in embryos and to search for the developmental regulators. We report a study of early Atlantic cod development that used a genome-wide oligonucleotide microarray to examine the composition and putative roles of polyadenylated transcripts.

Results

The analyses were carried out in unfertilized oocytes, newly fertilized oocytes and embryos at the stages of mid-blastula transition and segmentation. Numerous genes transcribed in oocytes are involved in multiple aspects of cell maintenance and protection, including metabolism, signal perception and transduction, RNA processing, cell cycle, defense against pathogens and DNA damage. Transcripts found in unfertilized oocytes also encoded a large number of proteins implicated in cell adherence, tight junction and focal adhesion, suggesting high complexity in terms of structure and cellular interactions in embryos prior to midblastula transition (MBT). Prezygotic transcripts included multiple regulators that are most likely involved in developmental processes that take place long after fertilization, such as components of ErbB, hedgehog, notch, retinoid, TGFb, VEGF and Wnt signaling pathways, as well as transcripts involved in the development of nervous system. The major event of MBT was the activation of a large group of histones and other genes that modify chromatin structure preceding massive gene expression changes. A hallmark of events observed during segmentation was the induction of multiple transcription factors, including a large group of homeobox proteins in pace with decay of a large fraction of maternal transcripts. Microarray analyses detected a suite of master developmental regulators that control differentiation and maintenance of diverse cell lineages.

Conclusions

Transcriptome profiling of the early stages in Atlantic cod revealed the presence of transcripts involved in patterning and development of tissues and organs long before activation of the zygotic genome. The switch from maternal to zygotic developmental programs is associated with large-scale modification of chromosomes.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-594) contains supplementary material, which is available to authorized users.

Seminal plasma microRNAs: potential biomarkers for spermatogenesis status

MicroRNAs (miRNAs) are small non-coding RNAs (18-25 nt), playing important regulatory roles via interaction with cellular messenger RNAs. The altered expression of miRNAs in specific tissues has been associated with diseases such as cancer and diabetes. We examined the presence of two selected miRNAs (miR-19b and let-7a) in human seminal plasma from fertile men and idiopathic infertile patients with oligozoospermia and non-obstructive azoospermia (NOA) using quantitative real-time PCR. We detected miRNAs in the seminal plasma of humans. The levels of miRNAs in the seminal plasma were reproducible in repeat samples from the same individuals. In addition, we examined the expression patterns of two selected miRNAs in 96 idiopathic infertile males (48 oligozoospermia and 48 NOA) and 48 fertile controls. Another 48 individuals of each group were used for verification. Our data showed that the expression levels of these two miRNAs in the seminal plasma significantly increased in idiopathic infertile males with NOA compared with fertile controls, whereas the expression levels were similar between idiopathic infertile males with oligozoospermia and fertile controls. In conclusion our results indicate that the expression of miR-19b and let-7a in the seminal plasma are reproducible and stable. Aberrant over-expression levels of miR-19b and let-7a may be an indicator of spermatogenic failure.

MicroRNA signature in testes-derived male germ-line stem cells

The testis-derived male germ-line stem (GS) cell, the in vitro counterpart of spermatogonial stem cell (SSC), can initiate donor-derived spermatogenesis in recipient testes and therefore, has been viewed as a future therapeutic modality for treatment of male infertility in azoospermic patients and in cancer patients who are expecting chemotherapy. Upon extended in vitro culture, GS cells also generate a second cell type called multipotent adult germ-line stem (maGS) cell which, upon testicular transplantation, produces teratoma instead of initiating spermatogenesis. Here, we show that expressions of both Let-7a and Let-7d were consistently higher while that of miR-294 (embryonic stem cell-cycle-regulating miRNA; ESCC) was lower in GS cells than in maGS cells. Furthermore, among several putative targets of Let-7 identified by in silico bioinformatics, expressions of Igf2 and H19 mRNA targets significantly differed between GS and maGS cells. However, although the CTCF binding factor (a component of DNA methylation machinery at Igf2-H19 cluster) was also a putative target for Let-7, the difference in expressions of Igf2 and H19 between GS and maGS cells was not mediated through a change in DNA methylation. Both GS and maGS cells maintained androgenetic imprinting at the Igf2-H19 imprinting control region and Peg1 differentially methylated region. In conclusion, our study suggests that high Let-7 expression may be a unique property of GS cells and expressions of Let-7 and ESCC miRNAs may serve as miRNA signatures to distinguish them from maGS cells during clinical transplantation, to avoid the likelihood of teratoma formation due to maGS cells generated during extended in vitro culture of GS cells.

Aromatase, oestrogens and human male reproduction

In most mammalian species aromatase is encoded by a single gene (Cyp19), which contains 18 exons, nine of them being translated. In man, the presence of a biologically active aromatase and oestrogen receptors (ERalpha and ERbeta) has been reported in Leydig cells, and also in immature germ cells and ejaculated spermatozoa. Concerning aromatase, the amount of transcript and enzymatic activity are decreased in immotile compared with motile sperm. We have amplified aromatase mRNA by real-time polymerase chain reaction in spermatozoa from asthenospermic, teratospermic and asthenoteratospermic men and recorded, respectively, 44, 52 and 67 per cent decreases of the amount of transcripts compared with fertile donors. A high degree of correlation (r = -0.64) between the abnormal spermatozoa (especially microcephaly and acrosome malformations) and aromatase/GAPDH transcript ratio has been observed. Idiopathic infertility is a wide health problem and no treatment is currently available. In humans, even if the role of oestrogens in spermatogenesis is still a matter of debate, the observations of decreased sperm number and motility in men genetically deficient in aromatase, together with our data and those reported in the literature, may suggest a role for aromatase/oestrogens not only during the development and maintenance of spermatogenesis but also in the final maturation of spermatozoa.

Sperm DNA: organization, protection and vulnerability: from basic science to clinical applications--a position report

This article reports the results of the most recent in a series of EHSRE workshops designed to synthesize the current state of the field in Andrology and provide recommendations for future work (for details see Appendix). Its focus is on methods for detecting sperm DNA damage and potential application of new knowledge about sperm chromatin organization, vulnerability and repair to improve the diagnosis and treatment of clinical infertility associated with that damage. Equally important is the use and reliability of these tests to identify the extent to which environmental contaminants or pharmaceutical agents may contribute to the incidence of sperm DNA damage and male fertility problems. A working group (for workshop details, see Appendix) under the auspices of ESHRE met in May 2009 to assess the current knowledgebase and suggest future basic and clinical research directions. This document presents a synthesis of the working group's understanding of the recent literature and collective discussions on the current state of knowledge of sperm chromatin structure and function during fertilization. It highlights the biological, assay and clinical uncertainties that require further research and ends with a series of 5 key recommendations.

Seasonal effect on sperm messenger RNA profile of domestic swine (Sus Scrofa)

Seasonal infertility is a well-known problem in the modern swine (Sus scrofa) industry. The molecular mechanisms responsible for thermal effects on spermatogenesis are, however, just beginning to be elucidated. The existence of specific messenger RNA (mRNA) remnants contained within freshly ejaculated sperm has been identified in several species. Investigators have obtained differential RNA profiles of infertile men compared with fertile individuals; however, there are limited to the probes, which are mostly derived from nucleic acids of testicular tissues of either human or mice. The objective of this study was to investigate mRNA remnants from ejaculated sperm of the domestic swine and uncover important clues regarding the molecular regulation of spermatogenesis under environmental thermo-impacts. We utilized the remnant mRNA collected from swine ejaculated sperm as the target source to detect the global gene expression in summer and in winter by swine sperm-specific oligonucleotide microarray. Sixty-seven transcripts were differentially expressed with statistical differences between seasons of sperm samples collected, including forty-nine in winter (49/67) and eighteen in summer (18/67). There were only 33 of these transcripts that could be annotated to gene ontology hierarchy with the database of Homo sapiens and their functions mostly were involved in variety of metabolic processes. Moreover, these studies also confirmed that significant differences of gene expression profiles were found in swine sperm when comparisons were made between ejaculates collected during the winter and the summer season under the subtropical area such as Taiwan. Even though most of the genes found in our experiments are still poorly understood in terms of their true functions in spermatogenesis, bioinformatics analysis suggested that they are involved in a broad spectrum of biochemical processes including gamete generation. These concordant profiles should permit the development of a non-invasive testing protocol to assess the functional capacity of sperm as well as a new molecular selection scheme for fine breeding swine.

Function of sperm chromatin structural elements in fertilization and development

Understanding how DNA is packaged in the mammalian sperm cell has important implications for human infertility as well as for the cell biology. Recent advances in the study of mammalian sperm chromatin structure and function have altered our perception of this highly condensed, inert chromatin. Sperm DNA is packaged very tightly to protect the DNA during the transit that occurs before fertilization. However, this condensation cannot sacrifice chromosomal elements that are essential for the embryo to access the correct sequences of the paternal genome for proper initiation of the embryonic developmental program. The primary levels of the sperm chromatin structure can be divided into three main categories: the large majority of DNA is packaged by protamines, a smaller amount (2-15%) retains histone-bound chromatin and the DNA is attached to the nuclear matrix at roughly 50 kb intervals. Current data suggest that the latter two structural elements are transferred to the paternal pronucleus after fertilization where they have important functional roles. The nuclear matrix organization is essential for DNA replication, and the histone-bound chromatin identifies genes that are important for embryonic development. These data support the emerging view of the sperm genome as providing, in addition to the paternal DNA sequence, a structural framework that includes molecular regulatory factors that are required for proper embryonic development.

The Preparation of Human Spermatozoal RNA for Clinical Analysis

The recent identification of RNA as a component of mature spermatozoa necessitated the development of a reliable isolation protocol capable of yielding a high-quality substrate. In addition to the inherent difficulties associated with isolating RNA, the procedure as applied to sperm must overcome the resilient nature and reduced RNA content found within this cell type. Further, the protocol must be suited to the clinical setting. A reliable RNA isolation procedure optimized for this unique cell type is described. Ejaculate is collected, contaminating somatic cells lysed then spermatozoal RNA released by homogenization in a chaotrope. RNA is then purified from the homogenate by chromatography using a commercially available resin. The quality of isolated samples is assessed by PCR and RT-PCR. Once purity is established samples are suitable for numerous applications including amplification and probe synthesis. The reliable and consistent isolation of high-quality RNA from mature spermatozoa will aid in the development of new tools for the clinical assessment of male-factor fertility.

Contributions of spermatozoa to embryogenesis: assays to evaluate their genetic and epigenetic fitness

During fertilization, spermatozoa contribute genetic and epigenetic factors that affect early embryogenesis. Genetic factors include a haploid genome with intact coding regions and regulatory regions for essential genes. The DNA must contain the proper copy number of essential genes, and cannot have increased single- or double- stranded DNA breaks. Epigenetic factors include a functional centrosome, proper packaging of the chromatin with protamines, modifications of histones, and imprinting of genes. Additionally, the fertilizing spermatozoon provides mRNAs and micro RNAs, which may contribute to the embryonic transcriptome and regulate embryonic gene expression. These epigenetic factors, directly or indirectly, affect the expression of genes in the developing embryo. Each of these contributions represents areas of potential sperm dysfunction, and they are the focus of ongoing research to develop assays which will allow further analysis of their clinical significance. This review briefly describes the current status of research into the genetic and epigenetic contributions of spermatozoa to embryogenesis, and the quest for clinical screening assays. The challenges to validation and clinical application of such testing are also discussed.

Paternal effects on early embryogenesis

Historically, less attention has been paid to paternal effects on early embryogenesis than maternal effects. However, it is now apparent that certain male factor infertility phenotypes are associated with increased DNA fragmentation and/or chromosome aneuploidies that may compromise early embryonic development. In addition, there is a growing body of evidence that the fertilizing sperm has more function than just carrying an intact, haploid genome. The paternally inherited centrosome is essential for normal fertilization, and the success of higher order chromatin packaging may impact embryogenesis. Epigenetic modifications of sperm chromatin may contribute to the reprogramming of the genome, and sperm delivered mRNA has also been hythesized to be necessary for embryogenesis. There is less information about the epigenetic factors affecting embryogenesis than genetic factors, but the epigenetics of gamete and early embryogenesis is a rapidly advancing field.

Relationship between chromatin organization, mRNAs profile and human male gamete quality

Spermiogenesis is a complex process leading to the formation of motile spermatozoa characterized by a highly stable chromatin compaction that transfers the paternal genome into the oocyte. It is commonly held that these haploid cells are devoid of transcriptional and translational activities and that the transcripts represent remnants of stored mRNAs. Recently, the chromatin organization of mature spermatozoa has been revisited as a double nucleoprotamine-nucleohistone structure possessing less-condensed regions sensitive to nuclease activity, which could be implicated in the expression of genes involved in the early embryo development. The existence of a complex population of mRNAs in human sperm is well-documented, but their role is not yet elucidated. Evidence for a latent transcriptional capacity and/or a potential de novo translation in mature spermatozoa from fertile men are essential for understanding the last steps of sperm maturation, such as capacitation and acrosome reaction. As such, we have documented the relationship between sperm quality and the distribution of sperm RNAs by showing divergent levels of transcripts encoding for proteins involved in either nuclear condensation (protamines 1 and 2) or in capacitation (eNOS and nNOS, c-myc) or in motility and sperm survival (aromatase) between low and high motile sperm issued from the same sample. Therefore, analyzing the profile of mRNAs could be helpful either as a diagnostic tool for evaluating male fertility after spermatogenesis or for prognosis use for fertilization.

RNA dynamics of fertile and infertile spermatozoa

The presence of a complex population of mRNAs in human mature spermatozoa is well documented; among them, transcripts of aromatase and ERs (oestrogen receptors) have been described but their significance is not clear. Therefore, to clarify the role of this complex population of mRNAs in human ejaculated sperm, we have isolated on discontinuous density gradients two main fractions from the same sample: high- and low-motile spermatozoa. The levels of different transcripts coding for molecules involved in nuclear condensation [Prm-1 (protamine 1) and Prm-2], capacitation [eNOS (endothelial nitric oxide synthase), nNOS (neuronal nitric oxide synthase), c-myc], motility and sperm survival (aromatase) have been assessed using semi-quantitative RT (reverse transcriptase)-PCR. The viability of sperm as well as the percentage of apoptosis were identical in high- and low-motile fractions. No significant change in the c-myc/Prm-2 ratio between the two populations of spermatozoa was observed. Conversely the amount of Prm-1 mRNA was significantly higher in low-motile than in high-motile fraction; in most of the high-motile sperm samples analysed, eNOS and nNOS transcripts were undetectable, whereas they were observed in low-motile sperm. Moreover, a partial or complete disappearance of c-myc transcripts was observed after capacitation. As to the aromatase expression, a significant decrease in the amount of transcripts in immotile sperm fraction was recorded in all samples studied. To conclude, analysing mRNA profiles in humans could be helpful either as a diagnostic tool to evaluate male fertility, since they reflect spermatogenesis gene expression, and/or a prognosis value for fertilization, since these RNAs are delivered to oocytes.

Differential expression of VASA gene in ejaculated spermatozoa from normozoospermic men and patients with oligozoospermia

AIM

To detect the expression of VASA in human ejaculated spermatozoa, and to compare the expression of VASA between normozoospermic men and patients with oligozoospermia.

METHODS

Ejaculated spermatozoa were collected from normozoospermic men and patients with oligozoospermia by masturbation, and subsequently segregated through a discontinuous gradient of Percoll to obtain the spermatozoa. Reverse transcription polymerase chain reaction (RT-PCR), quantitative RT-PCR (QRT-PCR), immunoflurescence and Western blotting were used to detect the expression of VASA in mRNA and protein levels.

RESULTS

VASA mRNA was expressed in the ejaculated spermatozoa. QRT-PCR analysis showed that VASA mRNA level was approximately 5-fold higher in normozoospermic men than that in oligozoospermic men. Immunofluorescence and Western blotting analysis showed that VASA protein was located on the cytoplasmic membrane of heads and tails of spermatozoa, and its expression was significantly decreased in oligozoospermic men, which is similar to the result of QRT-PCR.

CONCLUSION

The expression of VASA mRNA and protein was significantly decreased in the sperm of oligozoospermic men, which suggested the lower expression of the VASA gene might be associated with pathogenesis in some subtypes of male infertility and VASA could be used as a molecular marker for the diagnosis of male infertility.

Expression of CatSper family transcripts in the mouse testis during post-natal development and human ejaculated spermatozoa: relationship to sperm motility

CatSper is a unique sperm cation channel-like protein family exclusively expressed in the testis and plays important roles in sperm functions. The temporal expression profiles of CatSper1-4 mRNAs in the mouse testis during post-natal development through adulthood were investigated using real-time RT-PCR. The CatSper2 transcript was present in the testis of the 8-day-old mice, and was repressed in the adult testis after two sharp up-regulations at day 18 and 35. CatSper1 and CatSper3, 4 mRNAs were detectable in the testis of 18-day and 15-day-old mice, respectively. After sharp up-regulation at day 25 and 35, respectively, they were maximal at the adult testis stage. The differences between the temporal expression profiles of the CatSper transcripts in post-natal mouse testis development suggest different regulation to their transcription, and potentially contribute to the possibility of forming heteromeric channels among these four CatSper family members. CatSper1-3 transcripts were identified to be present in the human ejaculated spermatozoa by RT-PCR. Significantly higher levels of CatSper2 and CatSper3 mRNAs revealed by real-time RT-PCR were observed in the high-motile spermatozoa than in the low-motile fraction and suggests that CatSper2 and CatSper3 transcripts in the human ejaculated spermatozoa could be the potential targets for further study and male infertility screening.

Success and failure in human spermatogenesis as revealed by teratozoospermic RNAs

We are coming to appreciate that at fertilization human spermatozoa deliver the paternal genome alongside a suite of structures, proteins and RNAs. Although the role of some of the structures and proteins as requisite elements for early human development has been established, the function of the sperm-delivered RNAs remains a point for discussion. The presence of RNAs in transcriptionally quiescent spermatozoa can only be derived from transcription that precedes late spermiogenesis. A cross-platform microarray strategy was used to assess the profile of human spermatozoal transcripts from fertile males who had fathered at least one child compared to teratozoospermic individuals. Unsupervised clustering of the data followed by pathway and ontological analysis revealed the transcriptional perturbation common to the affected individuals. Transcripts encoding components of various cellular remodeling pathways, such as the ubiquitin-proteosome pathway, were severely disrupted. The origin of the perturbation could be traced as far back as the pachytene stage of spermatogenesis. It is anticipated that this diagnostic strategy will prove valuable for understanding male factor infertility.

The expression and significance of CATSPER1 in human testis and ejaculated spermatozoa

AIM

To investigate the distribution of cation channel of sperm 1 (CATSPER1) protein and the presence of CATSPER1 mRNA in human testis and ejaculated spermatozoa. The influence of anti-human CATSPER1 antibody upon human sperm motility was used to evaluate the function of human CATSPER1 and to estimate its possible use as a target for immunocontraception.

METHODS

Human ejaculated sperm from normozoospermic donors (n = 12) and liquid nitrogen frozen human testis were used for the study of mRNA and protein expression of CATSPER1 by reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry, respectively. Spermatozoa from normozoospermic donors (n = 12) were individually processed using a swim-up procedure and were then incubated with CATSPER1 antibody at final concentrations of 20, 4 and 0.8 microg/mL. After 1, 2 and 6 h incubation, progressive motility and fast progressive motility were measured by means of computer-assisted semen analysis.

RESULTS

CATSPER1 transcript was detected in both human testis and each human ejaculated semen sample. CATSPER1 protein expressed in the membrane of spermatid and was localized in the principal piece of the sperm tail. The application of CATSPER1 antibody at all concentrations significantly inhibited both progressive motility and fast progressive motility after 1, 2 and 6 h incubation, and significant dose-dependent changes were observed.

CONCLUSION

CATSPER1 is meiotically and post-meiotically expressed in human testis tissue. CATSPER1 mRNA in human ejaculated spermatozoa could be a more feasible target for study and infertility screening than testis biopsy. In addition, our results suggest that human CATSPER1 could be a possible target for immunocontraception.