A spermatogenesis-related gene expression profile in human spermatozoa and its potential clinical applications

The presence, role and clinical use of spermatozoal RNAs

BACKGROUND Spermatozoa are highly differentiated, transcriptionally inert cells characterized by a compact nucleus with minimal cytoplasm. Nevertheless they contain a suite of unique RNAs that are delivered to oocyte upon fertilization. They are likely integrated as part of many different processes including genome recognition, consolidation-confrontation, early embryonic development and epigenetic transgenerational inherence. Spermatozoal RNAs also provide a window into the developmental history of each sperm thereby providing biomarkers of fertility and pregnancy outcome which are being intensely studied. METHODS Literature searches were performed to review the majority of spermatozoal RNA studies that described potential functions and clinical applications with emphasis on Next-Generation Sequencing. Human, mouse, bovine and stallion were compared as their distribution and composition of spermatozoal RNAs, using these techniques, have been described. RESULTS Comparisons highlighted the complexity of the population of spermatozoal RNAs that comprises rRNA, mRNA and both large and small non-coding RNAs. RNA-seq analysis has revealed that only a fraction of the larger RNAs retain their structure. While rRNAs are the most abundant and are highly fragmented, ensuring a translationally quiescent state, other RNAs including some mRNAs retain their functional potential, thereby increasing the opportunity for regulatory interactions. Abundant small non-coding RNAs retained in spermatozoa include miRNAs and piRNAs. Some, like miR-34c are essential to the early embryo development required for the first cellular division. Others like the piRNAs are likely part of the genomic dance of confrontation and consolidation. Other non-coding spermatozoal RNAs include transposable elements, annotated lnc-RNAs, intronic retained elements, exonic elements, chromatin-associated RNAs, small-nuclear ILF3/NF30 associated RNAs, quiescent RNAs, mse-tRNAs and YRNAs. Some non-coding RNAs are known to act as epigenetic modifiers, inducing histone modifications and DNA methylation, perhaps playing a role in transgenerational epigenetic inherence. Transcript profiling holds considerable potential for the discovery of fertility biomarkers for both agriculture and human medicine. Comparing the differential RNA profiles of infertile and fertile individuals as well as assessing species similarities, should resolve the regulatory pathways contributing to male factor infertility. CONCLUSIONS Dad delivers a complex population of RNAs to the oocyte at fertilization that likely influences fertilization, embryo development, the phenotype of the offspring and possibly future generations. Development is continuing on the use of spermatozoal RNA profiles as phenotypic markers of male factor status for use as clinical diagnostics of the father's contribution to the birth of a healthy child.

Novel insights into the genetic and epigenetic paternal contribution to the human embryo

The integrity of the sperm genome and epigenome are critical for normal embryonic development. The advent of assisted reproductive technology has led to an increased understanding of the role of sperm in fertilization and embryogenesis. During fertilization, the sperm transmits not only nuclear DNA to the oocyte but also activation factor, centrosomes, and a host of messenger RNA and microRNAs. This complex complement of microRNAs and other non-coding RNAs is believed to modify important post-fertilization events. Thus, the health of the sperm genome and epigenome is critical for improving assisted conception rates and the birth of healthy offspring.

Analysis of Sperm Motility Related to Transcriptional Alterations of Mitocondrial Genes in Males Affected by Infertility

Infertility is a problem afflicting about 1/6 couples, and in 40% of cases this is primarily due to the male. Male infertility is a multifactorial pathology and it seems mainly related to sperm motility or sperm number. However, a diagnosis of infertility is frequently not followed by a precise explanation of its cause, reflecting our poor understanding of the spermatogenesis-related regulatory mechanisms and gene expression profiles. Therefore, this study was design to investigate the relative gene expression of a specific gene profile in ejaculate spermatozoa of men affected by infertility. This profile included 13 mitochondrial gene encoding subunits of respiratory chain and 7 nuclear sperm motility-related genes. We used values of progressive sperm motility (PR) to separate subjects affected by infertility into two groups, showing PR values higher (H group) or lower (L group) than the mean of the sample, and to classify fertile men (control group). We did not obtain a statistically significant difference in nuclear gene expression patterns in spermatozoa among these three groups. On the other hand, we observed an over-expression in 11/13 tested mitochondrial genes in the population of infertile males with altered sperm motility compared to the control group. This over-expression led us to speculate that there is an abnormal mRNA transcription of these 11 subunits, that impaired the normal energy supply ensuring sperm motility. Regarding the under-expression of 2/13 tested mitochondrial genes, we could assume that the spermatozoa mtDNA has accumulated mutations involving these two genes (CYB and ND4L). In conclusion, our results will provide useful information for the development of molecular diagnostic tools for clinical assessment of sperm health. However, further investigation into other sperm-related genes is needed to establish their roles in male fertility.

Pyruvate dehydrogenase complex: mRNA and protein expression patterns of E1α subunit genes in human spermatogenesis

During spermatogenesis, germ cells undergo a complex process of cell differentiation and morphological restructuring, which depends on the coordinated expression of different genes. Some vital examples are those involved in cell energy metabolism, namely the genes encoding the E1α subunit of pyruvate dehydrogenase complex: the somatic PDHA1 (X-linked) and the testis-specific PDHA2 (autosomal). There are no data related to the study at the RNA and protein levels of PDHA genes during human spermatogenesis. The present study aimed to describe the mRNA and protein expression patterns of the human PDHA genes during spermatogenesis. Expression profiles of the PDHA1 and PDHA2 genes were characterized using different human tissues and cells. Diploid and haploid germ cells fractions were obtained from testis tissues. The mRNA profiles were analyzed by quantitative RT-PCR, whereas the protein profiles were evaluated by immunohistochemistry, western blotting and two-dimensional electrophoresis. Expression of the PDHA1 gene was found in all somatic cells, whereas expression of PDHA2 gene was restricted to germ cells. The switch from X-linked to autosomic gene expression occurred in spermatocytes. Data suggest the activation of PDHA2 gene expression is most probably a mechanism to ensure the continued expression of the protein, thus allowing germ cell viability and functionality.

Key functional genes of spermatogenesis identified by microarray analysis

At present many couples face difficulties when trying to conceive that may have a genetic basis. The male factor is the cause of infertility as often as the female. Therefore it is important to identify key genes involved in spermatogenesis which may be linked to male infertility. This review discusses the identification of a range of genes associated with male fertility using microarrays. Based on differences in gene expression profiles between fertile and infertile male subgroups or between fetal and adult male gonads, many genes important for spermatogenesis have been discovered. Genes that are critical at particular stages of spermatogenesis were defined and can be considered as potential male fertility biomarkers. The studies described showed that microarrays may be potentially used as a diagnostic platform to increase the efficacy of diagnosis and perhaps treatment of infertile males.

Conserved properties of Drosophila and human spermatozoal mRNA repertoires

It is now well established that mature mammalian spermatozoa carry a population of mRNA molecules, at least some of which are transferred to the oocyte at fertilization, however, their function remains largely unclear. To shed light on the evolutionary conservation of this feature of sperm biology, we analysed highly purified populations of mature sperm from the fruitfly, Drosophila melanogaster. As with mammalian sperm, we found a consistently enriched population of mRNA molecules that are unlikely to be derived from contaminating somatic cells or immature sperm. Using tagged transcripts for three of the spermatozoal mRNAs, we demonstrate that they are transferred to the oocyte at fertilization and can be detected before, and at least until, the onset of zygotic gene expression. We find a remarkable conservation in the functional annotations associated with fly and human spermatozoal mRNAs, in particular, a highly significant enrichment for transcripts encoding ribosomal proteins (RPs). The substantial functional coherence of spermatozoal transcripts in humans and the fly opens the possibility of using the power of Drosophila genetics to address the function of this enigmatic class of molecules in sperm and in the oocyte following fertilization.

Differential RNAs in the sperm cells of asthenozoospermic patients

BACKGROUND

Alterations in RNAs present in sperm have been identified using microarrays in teratozoospermic patients and in other types of infertile patients. However, so far, there have been no reports on using microarrays to determine the RNA content of sperm from asthenozoospermic patients.

METHODS

We started the present project with the goal of characterizing the RNA abundance in the sperm cells of asthenozoospermic patients when compared with controls. To reach this objective, we initially selected four normal fertile donors and four asthenozoospermic infertile patients. Equal amounts of RNA were extracted from the sperm samples, subjected to different quality controls and hybridized to the Affymetrix U133 Plus version 2 arrays.

RESULTS

Several transcripts were identified that were present in different abundance in patients compared with controls. Subsequently, we validated the differential expression of three of the detected transcripts (ANXA2, BRD2 and OAZ3), using real-time PCR in a larger set of samples. A positive correlation between the expression of these transcripts and progressive motility was observed.

CONCLUSIONS

The sperm cells of asthenozoospermic patients contain an altered amount of some RNAs as detected using microarray analysis and subsequently validated using real-time PCR. These results open up the possibility to investigate the implication of these genes in the pathogenic mechanisms in asthenozoospermia and to consider their potential utility as infertility biomarkers.

Male reprotoxicity and endocrine disruption

Mammalian reproductive tract development is a tightly regulated process that can be disrupted following exposure to drugs, toxicants, endocrine-disrupting chemicals (EDCs), or other compounds via alterations to gene and protein expression or epigenetic regulation. Indeed, the impacts of developmental exposure to certain toxicants may not be fully realized until puberty or adulthood when the reproductive tract becomes sexually mature and altered functionality is manifested. Exposures that occur later in life, once development is complete, can also disrupt the intricate hormonal and paracrine interactions responsible for adult functions, such as spermatogenesis. In this chapter, the biology and toxicology of the male reproductive tract is explored, proceeding through the various life stages including in utero development, puberty, adulthood, and senescence. Special attention is given to the discussion of EDCs, chemical mixtures, low-dose effects, transgenerational effects, and potential exposure-related causes of male reproductive tract cancers.

Cleavage of rRNA ensures translational cessation in sperm at fertilization

Intact ribosomal RNAs (rRNAs) comprise the majority of somatic transcripts, yet appear conspicuously absent in spermatozoa, perhaps reflecting cytoplasmic expulsion during spermatogenesis. To discern their fate, total RNA retained in mature spermatozoa from three fertile donors was characterized by Next Generation Sequencing. In all samples, >75% of total sequence reads aligned to rRNAs. The distribution of reads along the length of these transcripts exhibited a high degree of non-uniformity that was reiterated between donors. The coverage of sequencing reads was inversely correlated with guanine-cytosine (GC)-richness such that sequences greater than ∼70% GC were virtually absent in all sperm RNA samples. To confirm the loss of sequence, the relative abundance of specific regions of the 28S transcripts in sperm was established by 7-Deaza-2'-deoxy-guanosine-5'-triphosphate RT-PCR. The inability to amplify specific regions of the 28S sequence from sperm despite the abundant representation of this transcript in the sequencing libraries demonstrates that approximately three-quarters of RNA retained in the mature male gamete are products of rRNA fragmentation. Hence, cleavage (not expulsion of the RNA component of the translational machinery) is responsible for preventing spurious translation following spermiogenesis. These results highlight the potential importance of those transcripts, including many mRNAs, which evade fragmentation and remain intact when sperm are delivered at fertilization. Sequencing data are deposited in GEO as: GSE29160.

Integrative DNA methylation and gene expression analyses identify DNA packaging and epigenetic regulatory genes associated with low motility sperm

Background

In previous studies using candidate gene approaches, low sperm count (oligospermia) has been associated with altered sperm mRNA content and DNA methylation in both imprinted and non-imprinted genes. We performed a genome-wide analysis of sperm DNA methylation and mRNA content to test for associations with sperm function.

Methods and Results

Sperm DNA and mRNA were isolated from 21 men with a range of semen parameters presenting to a tertiary male reproductive health clinic. DNA methylation was measured with the Illumina Infinium array at 27,578 CpG loci. Unsupervised clustering of methylation data differentiated the 21 sperm samples by their motility values. Recursively partitioned mixture modeling (RPMM) of methylation data resulted in four distinct methylation profiles that were significantly associated with sperm motility (P = 0.01). Linear models of microarray analysis (LIMMA) was performed based on motility and identified 9,189 CpG loci with significantly altered methylation (Q<0.05) in the low motility samples. In addition, the majority of these disrupted CpG loci (80%) were hypomethylated. Of the aberrantly methylated CpGs, 194 were associated with imprinted genes and were almost equally distributed into hypermethylated (predominantly paternally expressed) and hypomethylated (predominantly maternally expressed) groups. Sperm mRNA was measured with the Human Gene 1.0 ST Affymetrix GeneChip Array. LIMMA analysis identified 20 candidate transcripts as differentially present in low motility sperm, including HDAC1 (NCBI 3065), SIRT3 (NCBI 23410), and DNMT3A (NCBI 1788). There was a trend among altered expression of these epigenetic regulatory genes and RPMM DNA methylation class.

Conclusions

Using integrative genome-wide approaches we identified CpG methylation profiles and mRNA alterations associated with low sperm motility.

Major chimpanzee-specific structural changes in sperm development-associated genes

A comprehensive analysis of transcriptional structures of chimpanzee sperm development-associated genes is of significant interest for deeply understanding sperm development and male reproductive process. In this study, we sequenced 7,680 clones from a chimpanzee testis full-length cDNA library and obtained 1,933 nonredundant high-quality full-length cDNA sequences. Comparative analysis between human and chimpanzee showed that 78 sperm development-associated genes, most of which were yet uncharacterized, had undergone severe structural changes (mutations at the start/stop codons, INDELs, alternative splicing variations and fusion forms) on genomic and transcript levels throughout chimpanzee evolution. Specifically, among the 78 sperm development-associated genes, 39 including ODF2, UBC, and CD59 showed markedly chimpanzee-specific structural changes. Through dN/dS analysis, we found that 56 transcripts (including seven sperm development-associated genes) had values of greater than one when comparing human and chimpanzee DNA sequences, whereas the values were less than one when comparing humans and orangutans. Gene ontology annotation and expression profiling showed that the chimpanzee testis transcriptome was enriched with genes that are associated with chimpanzee male germ cell development. Taken together, our study provides the first comprehensive molecular evidence that many chimpanzee sperm development-associated genes had experienced severe structural changes over the course of evolution on genomic and transcript levels.

Fluoride-induced apoptosis and gene expression profiling in mice sperm in vivo

Exposure to fluoride can induce low sperm quality; however, little is known about the molecular mechanisms by which fluoride exerts its toxic effects. This study was conducted to evaluate ultrastructure, oxidative stress, and apoptosis in sperm of mice treated with 150 mg/l NaF for 49 days. Furthermore, microarray analysis was also utilized to characterize the effects of fluoride in gene expression profiling on mice sperm. An increased ROS and a decreased TAC accompanied with distinct morphological changes and significant apoptosis were observed in mice sperm from the fluoride group. Fluoride exposure also significantly elevated the protein expressions of cytochrome c and active caspase-3. In global gene expression profiling, 34 up-regulated and 63 down-regulated genes, which are involved in several sperm biological processes including signal transduction, oxidative stress, apoptosis, electron transport, glycolysis, chemotaxis, spermatogenesis, and sperm capacitation, were significantly differentially expressed. Based on these findings, it was proposed that oxidative stress induced by excessive ROS may trigger sperm apoptosis through mitochondrial impairment, resulting in decreased fertility in mice exposed to fluoride. Microarray analysis also provided several important biological clues for further investigating fluoride-induced damage in sperm morphology and functions.

Genetic and epigenetic factors: Role in male infertility

Genetic factors contribute upto 15%-30% cases of male infertility. Formation of spermatozoa occurs in a sequential manner with mitotic, meiotic, and postmeiotic differentiation phases each of which is controlled by an intricate genetic program. Genes control a variety of physiologic processes, such as hypothalamus-pituitary-gonadal axis, germ cell development, and differentiation. In the era of assisted reproduction technology, it is important to understand the genetic basis of infertility to provide maximum adapted therapeutics and counseling to the couple.

Testicular postgenomics: targeting the regulation of spermatogenesis

Sperm are, arguably, the most differentiated cells produced within the body of any given species. This is owing to the fact that spermatogenesis is an intricate and highly specialized process evolved to suit the individual particularities of each sexual species. Despite a vast diversity in method, the aim of spermatogenesis is always the same, the idealized transmission of genetic patrimony. Towards this goal certain requirements must always be met, such as a relative twofold reduction in ploidy, repackaging of the chromatin for transport and specialized enhancements for cell motility, recognition and fusion. In the past 20 years, the study of molecular networks coordinating male germ cell development, particularly in mammals, has become more and more facilitated thanks to large-scale analyses of genome expression. Such postgenomic endeavors have generated landscapes of data for both fundamental and clinical reproductive biology. Continuous, large-scale integration analyses of these datasets are undertaken which provide access to very precise information on a myriad of biomolecules. This review presents commonly used transcriptomic and proteomic workflows applied to various testicular germ cell studies. We will also provide a general overview of the technical possibilities available to reproductive genomic biologists, noting the advantages and drawbacks of each technique.

Analysis and difference of voltage-dependent anion channel mRNA in ejaculated spermatozoa from normozoospermic fertile donors and infertile patients with idiopathic asthenozoospermia

PURPOSE

to analyze the abundance and difference of voltage-dependent anion channel (VDAC) mRNA in ejaculated spermatozoa from normozoospermic fertile donors and infertile patients with idiopathic asthenozoospermia.

METHODS

high motile and low motile spermatozoa were separated respectively from ejaculates of 36 donors and 40 patients using a discontinuous Percoll gradient centrifugation. Real-Time PCR was performed to detect mRNA abundance and difference of three VDAC subtypes between two groups with different sperm motility.

RESULTS

real-Time PCR demonstrated that three VDAC mRNAs were present in mature spermatozoa. The VDAC2 mRNA level in ejaculated spermatozoa of patients was significantly higher than that of donors. No significant differences of VDAC1 and VDAC3 mRNA levels were found between two groups.

CONCLUSION

the high abundance of VDAC2 mRNA seemed to have a positive correlation with low sperm motility. The abnormal expression of VDAC might be related to male infertility with idiopathic asthenozoospermia.

The making of abnormal spermatozoa: cellular and molecular mechanisms underlying pathological spermiogenesis

Fertilization in mammals occurs via a series of well-defined events in the secluded environment of the female reproductive tract. The mode of selection of the fertilizing spermatozoon nevertheless remains unknown. As has become evident during in vitro fertilization by sperm microinjection into the oocyte, abnormal spermatozoa can successfully fertilize oocytes. Under these extreme conditions, post-fertilization events, early embryonic development and implantation are significantly compromised indicating that the contribution of spermatozoa extends beyond sperm penetration. Microscopic identification of normal spermatozoa is a well-standardized procedure but insights into the mechanisms that lead to aberrant sperm differentiation and into the subcellular nature of sperm abnormalities have only recently begun to be obtained. The spermatozoon is the result of a complex development in which spermatid organelles give rise to various structural components with characteristic functions. Similar to other differentiated cells, the spermatozoon has a specific pathology that is most clearly identified by ultrastructural evaluation coupled with immunocytochemistry and molecular techniques. This multidisciplinary approach allows the precise characterization of sperm abnormalities, including structural, molecular and functional aspects. We summarize here studies of the physiopathology of spermiogenesis in two abnormal sperm phenotypes of infertile men: dysplasia of the fibrous sheath and acephalic spermatozoa/abnormal head-tail attachment. The characterization of the abnormalities of the tail cytoskeleton and centrioles has uncovered aspects of the subcellular basis of pathological spermiogenesis, has suggested experimental approaches to explore the nature of these anomalies and has opened the way for genetic studies that will ultimately lead to the design of the therapeutic tools of the future.

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.

Spermatozoal RNAs: what about their functions?

The profound architectural changes that transform spermatids into spermatozoa result in a high degree of DNA packaging within the sperm head. However, the mature sperm chromatin that harbors imprinted genes exhibits a dual nucleoprotamine/nucleohistone structure with DNase-sensitive regions, which could be implicated in the establishment of efficient epigenetic information in the developing embryo. Despite its apparent transcriptionally inert state, the sperm nucleus contains diverse RNA populations, mRNAs, antisense and miRNAs, that have been transcribed throughout spermatogenesis. There is also an endogenous reverse transcriptase that may be activated under certain circumstances. It is now commonly accepted that sperm can deliver some RNAs to the ovocyte at fertilization. This review presents potential links between male-specific genomic imprinting, chromatin organization, and the presence of diverse RNA populations within the sperm nucleus and discusses the functional significance of these RNAs in the spermatozoon itself and in the early embryo following fertilization. Some recent data are provided, supporting the view that analyzing the profile of spermatozoal RNAs could be useful for assessment of male fertility.

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.

Role of translation by mitochondrial-type ribosomes during sperm capacitation: an analysis based on a proteomic approach

Mammalian spermatozoa contain a complex population of mRNAs, some of which have been demonstrated to be translated de novo by mitochondrial-type ribosomes using D-chloramphenicol (CP), a specific inhibitor of mitochondrial translation. However, little is known about the functions of these mRNAs in mature sperm. In the present study, differential proteomic approaches were applied to study sperm protein profiles translated by mitochondrial-type ribosomes using the inhibitor CP and 44 proteins were identified with lower expression in CP-treated sperm in comparison to capacitated sperm (ratio >or= 1.5, p<0.05). Results of Western blot and real-time PCR suggest that four proteins were translated by mitochondrial-type ribosomes. Bioinformatics analysis indicated that 26 of 44 proteins were involved in some critical processes correlated to sperm-egg interaction event. In addition, Mups, whose functions in reproduction have never been studied, were chosen for further study. Our results showed that Mups proteins were localized to the acrosome and flagellum of precapacitated sperm, and were also expressed in the equatorial segment of capacitated sperm. The depletion of Mups using neutralizing antibodies significantly inhibited capacitation in a dose-dependent manner, subsequently inhibited acrosome reaction and sperm-egg fusion. In summary, mitochondrial translation during capacitation can store proteins beneficial for sperm-egg interaction.

Male gamete survival at stake: causes and solutions

Over the years, the development of assisted reproductive technology to bypass male factor infertility has improved drastically. Considered one of the most perplexing disorders in the reproductive field, male factor infertility is prevalent and may be on the rise. Unfortunately, its aetiology remains elusive. One of the main reasons lies in the complex machinery and structure of the hydrodynamic sperm cell. Its polyunsaturated fatty acid cell membrane, the protamines in its genetic material and the absence of antioxidants in its cytoplasm ensure that the spermatozoon is highly susceptible to environmental effects. The spermatozoon's genesis, storage, and transport through the male reproductive tract are also susceptible, genetically and pathologically, to environmental effects. This review aims to include all the possible causes of disruption to this unique cell and their probable solutions, in the hope of clearing up the ambiguity that surrounds male factor infertility.

Pregnancy-specific {beta}-1-glycoprotein 1 and human leukocyte antigen-E mRNA in human sperm: differential expression in fertile and infertile men and evidence of a possible functional role during early development

BACKGROUND

Mature spermatozoa contain thousands of mRNA transcripts. It has been recently shown that human sperm can deliver RNA into the oocyte, suggesting that mRNAs might have a role before or after fertilization. Human embryos express PSG1 (pregnancy-specific beta-1-glycoprotein 1) and HLA-E (human leukocyte antigen-E), molecules playing a role in implantation and early development. We compared PSG1 and HLA-E sperm mRNA levels in fertile and infertile men and we tested the hypothesis that these transcripts are selectively retained in the newly formed zygote.

METHODS

Real-time RT-PCR was used to analyze sperm mRNA levels (n = 11 fertile, n = 31 infertile patients) of PSG1, HLA-E and PRM2 (protamine 2). The presence of PSG1 and HLA-E proteins was evaluated by western blot in sperm protein extracts (n = 3). Using ICSI of human sperm into hamster oocytes we evaluated the permanence of these mRNAs at different time points (n = 10 for each time) after fertilization.

RESULTS

PSG1, HLA-E and PRM2 transcripts were demonstrated in ejaculated sperm. The fertile group showed significantly higher levels of PSG1 and HLA-E mRNA (both P < 0.05) than the infertile group, whereas PRM2 levels were not significantly different. However, PSG1 and HLA-E proteins were not found in ejaculated sperm. Following ICSI, PRM2 was undetectable after fertilization; conversely, PSG1 and HLA-E transcripts remained detectable for at least 24 h of zygotic development.

CONCLUSIONS

We provide new evidence that indicates that human sperm deliver transcripts that may have a role in early embryo development and decreased levels of these transcripts may be associated with infertility.

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.

Spermatozoal RNA as reservoir, marker and carrier of epigenetic information: implications for cloning

The mammalian male gamete is transcriptionally silent as a consequence of the highly condensed architecture of its chromatin and there is also little or no cytoplasm capable of supporting translation; however, we now understand that under certain conditions, spermatozoa can translate their mRNAs de novo and that spermatozoal RNA can potentially affect phenotypic traits in offspring. This epigenetic phenomenon may involve the transmission of extra-chromosomal episomal elements. Recent evidence indicates that spermatozoal RNA may play a role in the progressive shutdown of transcription during spermiogenesis. The presence of RNA in the sperm nucleus and its potential as a carrier of epigenetic information to the egg may prove insightful with regard to the abysmal success rates for cloning of domestic species by somatic nuclear transfer procedures.

TSPY gene copy number as a potential new risk factor for male infertility

The human TSPY (testis-specific protein, Y-linked) gene family (30-60 copies) is situated in the MSY (male-specific) region of the Y chromosome. Testis-specific expression indicates that the gene plays a role in spermatogenesis. Refined quantitative fluorescence PCR (polymerase chain reaction) was applied to evaluate the relative number of TSPY copies compared with AMELY/X (amelogenin gene, Y-linked) genes in 84 stratified infertile men and in 40 controls. A significantly higher number of TSPY copies was found in infertile men compared with the controls (P = 0.002). The diagnostic discrimination potential of the relative number of TSPY copies was evaluated by receiver operating characteristic curve analysis. TSPY/AMELY was unambiguously found to be powerful in the diagnostic separation of both the control samples and the infertile men, reaching a good level of specificity (0.642) and sensitivity (0.732) at a cut-off point of 0.46. The findings were supported by independently repeated studies of randomly selected positive samples and controls. Evaluation of the TSPY copy number offers a completely new diagnostic approach in relation to the genetic cause of male infertility. The possible effect of the copy number of TSPY genes on spermatogenesis may explain indiscrete pathological alterations of spermatid quality and quantity.

Molecular basis of sex and reproductive status in breeding zebrafish

The zebrafish ( Danio rerio) is used extensively as a model species for studies on vertebrate development and for assessing chemical effects on reproduction. Despite this, the molecular mechanisms controlling zebrafish reproduction are poorly understood. We analyzed the transcriptomic profiles of the gonads of individual zebrafish, using a 17k oligonucleotide microarray, to define the molecular basis of sex and reproductive status in sexually mature fish. The gonadal transcriptome differed substantially between sexes. Among the genes overexpressed in females, 11 biological processes were overrepresented including mitochondrion organization and biogenesis, and cell growth and/or maintenance. Among the genes overexpressed in males, six biological processes were overrepresented including protein biosynthesis and protein metabolism. Analysis of the expression of gene families known to be involved in reproduction identified a number of genes differentially expressed between ovaries and testes including a number of sox genes and genes belonging to the insulin-like growth factor and the activin-inhibin pathways. Real-time quantitative PCR confirmed the expression profiles for nine of the most differentially expressed genes and indicated that many transcripts are likely to be switched off in one of the sexes in the gonads of adult fish. Significant differences were seen between the gonad transcriptomes of individual reproductively active females reflecting their stage of maturation, whereas the testis transcriptomes were remarkably similar between individuals. In summary, we have identified molecular processes associated with (gonadal) sex specificity in breeding zebrafish and established a strong relationship between individual ovarian transcriptomes and reproductive status in females.

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.

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.

Emerging technologies for the molecular study of infertility, and potential clinical applications

The techniques currently used to treat infertility cases are quite limited in their capabilities, due to an incomplete understanding of the molecular activities of germ cells. Fortunately, several technologies are presently being researched that should aid the understanding of the various molecular causes of germ cell pathologies. This review discusses microarray technology, proteomics, metabolic profiling, the PolScope, atomic force microscopy and microfluidics. These technologies have all seen success in preliminary studies, and promise directly or indirectly to improve the low success rates of IVF and other related therapies. However, their widespread use in laboratories and clinics may not be seen until preliminary studies confirming their safety and effectiveness are published, and until standardized protocols for their utilization are established.

Spermatozoal RNA: why is it there and what does it do?

The mammalian male gamete is transcriptionally silent as a consequence of the highly condensed architecture of its chromatin and there is also little or no cytoplasm capable of supporting translation; however, we now understand that these cells carry a full complement of mRNAs and that under certain conditions, spermatozoa can translate their mRNAs de novo. Moreover, there is now good evidence that spermatozoal RNA can potentially affect phenotypic traits in offspring. This epigenetic phenomenon may involve the transmission of extra-chromosomal episomal elements. These data indicate that the spermatozoon is well matched to its role of delivering the paternal genome, but that additional male-benefits may also be accrued by the delivery of spermatozoal RNA.

Towards a better understanding of RNA carriage by ejaculate spermatozoa

Research on spermatozoal RNA has made considerable progress since the original reports on its presence appeared in the late 1950s and early 1960s. Through the use of stringent procedures aimed at eliminating contamination artefacts, we now appreciate that a complex cohort of mRNAs persists in the ejaculate cell but that 80S (cytoplasmic) ribosomal complexes are not present in sufficient quantities to support cytoplasmic mRNA translation. Despite this, under certain conditions, at least some cytoplasmic mRNAs can apparently be translated de novo, possibly on mitochondrial polysomes. The detection of mRNA translation by mature spermatozoa essentially supports the earliest research reports on spermatozoal gene expression although the suggested relationship with protein turnover and capacitation is wholly unexpected. We also examine some alternative explanations and roles for RNA carriage, including the RNAs passive retention as a consequence of nuclear shutdown and a more active role in chromatin repackaging, genomic imprinting, gene silencing and post-fertilization requirements of essential paternal RNAs. The recent report of an RNA-mediated epigenetic alteration to phenotype that is likely to be sperm derived is of particular interest in this regard. We finally show that regardless of the biological role(s) of spermatozoal RNA, its utility in infertility studies, particularly when coupled with modern techniques in gene-expression analysis (e.g. microarrays), is obvious. As a wholly non-invasive proxy for the testis, this RNA offers considerable potential as a marker for fertility status and the genetic and environmental influences that could make all the difference between a fertile and an infertile phenotype.

Human testis specific protein 1 expression in human spermatogenesis and involvement in the pathogenesis of male infertility

Human testis specific protein 1 (TPX1) exists in the cytomembrane and cytoplasm of spermatogenic cells from pachytene spermatocytes to elongated spermtids, including pachytene spermatocytes, round spermtids and elongated spermtids. It is localized in the connecting piece, the flagellum, and the acrosome of mature human spermatozoa. The protein level and localization of TPX1 were altered in patients with spermatogenic arrest and in infertile men with oligoasthenoteratospermia syndrome.

Different expression and activity of the alpha1 and alpha4 isoforms of the Na,K-ATPase during rat male germ cell ontogeny

Two catalytic isoforms of the Na,K-ATPase, alpha1 and alpha4, are present in testis. While alpha1 is ubiquitously expressed in tissues, alpha4 predominates in male germ cells. Each isoform has distinct enzymatic properties and appears to play specific roles. To gain insight into the relevance of the Na,K-ATPase alpha isoforms in male germ cell biology, we have studied the expression and activity of alpha1 and alpha4 during spermatogenesis and epididymal maturation. This was explored in rat testes at different ages, in isolated spermatogenic cells and in spermatozoa from the caput and caudal regions of the epididymis. Our results show that alpha1 and alpha4 undergo differential regulation during development. Whereas alpha1 exhibits only modest changes, alpha4 increases with gamete differentiation. The most drastic changes for alpha4 take place in spermatocytes at the mRNA level, and with the transition of round spermatids into spermatozoa for expression and activity of the protein. No further changes are detected during transit of spermatozoa through the epididymis. In addition, the cellular distribution of alpha4 is modified with development, being diffusely expressed at the plasma membrane and intracellular compartments of immature cells, finally to localize to the midregion of the spermatozoon flagellum. In contrast, the alpha1 isoform is evenly present along the plasma membrane of the developing and mature gametes. In conclusion, the Na,K-ATPase alpha1 and alpha4 isoforms are functional in diploid, meiotic and haploid male germ cells, alpha4 being significantly upregulated during spermatogenesis. These results support the importance of alpha4 in male gamete differentiation and function.

Toward using stable spermatozoal RNAs for prognostic assessment of male factor fertility

OBJECTIVE

To establish the stability of spermatozoal RNAs as a means to validate their use as a male fertility marker.

DESIGN

Semen samples were randomly selected for 1 of 3 cryopreservation treatments.

SETTING

An academic research environment.

PATIENT(S)

Men aged 19 to 55 years who had fathered a child by natural conception within the past 6 months.

INTERVENTION(S)

Ejaculates were collected by masturbation and total spermatozoan RNA was isolated from two semen samples of ideal quality; one sample of medium quality, having been subjected to an additional freeze-thaw cycle, and two samples of poor quality, having been subjected to a third freeze-thaw cycle.

MAIN OUTCOME MEASURE(S)

Labeled cDNAs were generated and then used to interrogate Atlas Nylon Human Toxicology 1.2 microarrays. The spermatozoan transcriptomes were compared using a binomial approach.

RESULT(S)

The analysis identified a total of 228 unique spermatozoal transcripts among all samples. The medium quality sample shared 98% and 39% of its RNAs with the ideal and poor quality samples, respectively. A set of 36 RNAs resistant to insult were observed, some of which have been implicated in regulating male fertility, when all individuals were compared.

CONCLUSION(S)

These results support the view that a population of spermatozoal RNAs is rapidly degraded in response to insult, whereas another population appears protected from such damage. Because spermatozoal RNAs echo the gene expression of spermatogenesis, the latter is likely to prove useful as a clinical maker of fertility status.

Expression of a novel beta adaptin subunit mRNA splice variant in human testes

AIM

To identify a novel isoform of adaptin 2 beta subunit (named Ap2beta-NY) and to investigate its relationship with testicular development and spermatogenesis.

METHODS

Using a human testis cDNA microarray, a clone (Ap2beta-NY), which was strongly expressed in adult testes but weakly expressed in embryo testes, was sequenced and analyzed. Using polymerase chain reaction (PCR), the tissue distribution and expression time pattern of Ap2beta-NY were determined.

RESULTS

Ap2beta-NY was identified and has been deposited in the GenBank (AY341427). The expression level of Ap2beta-NY in the adult testis was about 3-fold higher than that in the embryo testis. PCR analysis using multi-tissue cDNA indicated that Ap2beta-NY was highly expressed in the testis, spleen, thymus, prostate, ovary, blood leukocyte and brain, but not in the heart, placenta, lung, liver, skeletal muscle, kidney and pancreas. In addition, Ap2beta-NY was variably expressed in the testes of patients with spermatogenesis-disturbance and spermatogenesis-arrest but not expressed in those of Sertoli-cell-only syndrome, which implied that, in the testis, Ap2beta-NY was restrictively expressed in germ cells.

CONCLUSION

Ap2beta-NY is an isoform of Ap2beta and may be involved in regulating the process of spermatogenesis and testis development.

Expression of a novel alternative transcript of the novel retinal pigment epithelial cell gene NORPEG in human testes

AIM

To identify a novel alternative transcript of the novel retinal pigment epithelial cell gene (NORPEG) expressed in the human testis.

METHODS

A human testis cDNA microarray was established and hybridized with cDNA probes from human fetal testes, adult testes and human spermatozoa. Differentially expressed clones were sequenced and analyzed. One of these clones was a short transcript of NORPEG which we proceeded to analyze by RT-PCR.

RESULTS

The novel short alternative transcript of NORPEG was isolated and named sNORPEG. It was 3486 bp in length and contained a 2952-bp open reading frame, encoding a 110.4-kDa protein of 983 amino acids. Amino acid sequence analysis showed that the sNORPEG protein contains six ankyrin repeats and two coiled-coil domains. It shares a high homology with the NORPEG and ankycorbin proteins in both its sequence and motifs. Blasting the human genome database localized sNORPEG to human chromosome 5p13.2-13.3. Expression profiles showed that sNORPEG was expressed in human fetal testes, adult testes and spermatozoa. Moreover, sNORPEG was found to be ubiquitously expressed in human tissues.

CONCLUSION

sNORPEG is expressed in different developmental stages of the testis and encodes a protein that may have roles in human testis development and spermatogenesis.