An intact sperm nuclear matrix may be necessary for the mouse paternal genome to participate in embryonic development

The Assessment of Sperm DNA Integrity: Implications for Assisted Reproductive Technology Fertility Outcomes across Livestock Species

Sperm DNA integrity is increasingly considered a useful measure of semen quality in mammalian reproduction. However, the definition of DNA integrity, the ideal means by which it should be measured, and its predictive value for fertility remain a topic of much discussion. With an emphasis on livestock species, this review discusses the assays that have been developed to measure DNA integrity as well as their correlation with in vitro and in vivo fertility.

Prediction of Nili-Ravi buffalo bull fertility through Fourier harmonic analysis of sperm

Fourier harmonic analysis (FHA) is a robust method for identification of minute changes in sperm nuclear shape that are indicative of reduced fertility. The current study was designed to develop a fertility prediction model for Nili-Ravi buffalo bulls through FHA of sperm. In experiment I, FHA technique was standardized, average sperm nuclear perimeter was measured and sperm nuclear shape plot of buffalo bull was constructed. Sperm of buffalo bulls (n = 10) were stained with YOYO-1 and Hoechst-33342 to differentiate live and dead, and digital images were captured using phase contrast and fluorescent microscopy. The images were analyzed by ImageJ software and 100 sperm/bull were evaluated. The results are described as mean ± SEM values of mean harmonic amplitude (mharm), skewness harmonic amplitude (skharm), kurtosis harmonic amplitude (kurharm) and variance harmonic amplitude (varharm) at Fourier frequencies 0-5 along with the cartesian and polar coordinate plots of buffalo bull sperm. In experiment II, a fertility prediction model was developed based on FHA of buffalo bull sperm. Semen samples of low (n = 6), medium (n = 3) and high (n = 8) fertility bulls were investigated for FHA of sperm and harmonic amplitudes (HA) were generated. Firstly, to determine if live and dead sperm population have unique nuclear shape distribution; the mean, skewness, kurtosis and variance HA 0-5 of 1700 live and 1294 dead spermatozoa of 17 bulls were evaluated. T-test signified a difference in the mharm0 (2.363 ± 0.01 vs. 2.439 ± 0.02), skharm0 (-0.0002 ± 0.07 vs. -0.266 ± 0.09), kurharm0 (-0.156 ± 0.07 vs. 0.260 ± 0.18), kurharm2 (0.142 ± 0.11 vs. 1.031 ± 0.32) and varharm4 (0.109 ± 0.00 vs. 0.082 ± 0.00) of live vs. dead sperm population (p < 0.05). Therefore, 100 live sperm/bull were further evaluated for mean, skewness, kurtosis and variance HA 0-5 values among high (n = 6) and low-fertility (n = 6) groups. Results of T-test showed higher values of mharm2 (0.739 ± 0.01 vs. 0.686 ± 0.00), mharm4 (0.105 ± 0.001 vs. 0.007 ± 0.001), and skharm0 (0.214 ± 0.109 vs. -0.244 ± 0.097) in high vs. low-fertility group (p < 0.05). In next step, five significantly different combinations of discriminant measures between high and low-fertility groups were obtained by discriminant analysis. In conclusion, mharm4, skharm0 and varharm2 correctly identified 91.7 % of bulls into their respective fertility groups, and upon cross validation the value of the canonical correlation was 0.928.

Review: Evaluation of bull fertility. Functional and molecular approaches

With the term "assisted reproduction technologies" in modern cattle farming, one could imply the collection of techniques that aim at the optimal use of bovine gametes to produce animals of high genetic value in a time- and cost-efficient manner. The accurate characterisation of sperm quality plays a critical role for the efficiency of several assisted reproduction-related procedures, such as sperm processing, in vitro embryo production and artificial insemination. Bull fertility is ultimately a collective projection of the ability of a series of ejaculates to endure sperm processing stress, and achieve fertilisation of the oocyte and production of a viable and well-developing embryo. In this concept, the assessment of sperm functional and molecular characteristics is key to bull fertility diagnostics and prognostics. Among others, functional features linked to sperm plasma membrane, acrosome and DNA integrity are usually assessed as a measure of the ability of sperm to express the phenotypes that will allow them to maintain their homeostasis and orchestrate-in a strict temporal manner-the course of events that will enable the delivery of their genetic content to the oocyte upon fertilisation. Nevertheless, measures of sperm functionality are not always adequate indicators of bull fertility. Nowadays, advancements in the field of molecular biology have facilitated the profiling of several biomolecules in male gametes. The molecular profiling of bovine sperm offers a deeper insight into the mechanisms underlying sperm physiology and, thus, can reveal novel candidate markers for bull fertility prognosis. In this review, the importance of three organelles (the nucleus, the plasma membrane and the acrosome) for the characterisation of sperm fertilising capacity and bull fertility is discussed at functional and molecular levels. In particular, information about sperm head morphometry, chromatin structure, viability as well as the ability of sperm to capacitate and undergo the acrosome reaction are presented in relation to the cryotolerance of male gametes and bull fertility. Finally, major spermatozoal coding and non-coding RNAs, and proteins that are involved in the above-mentioned aspects of sperm functionality are also summarised.

Telomere Distribution in Human Sperm Heads and Its Relation to Sperm Nuclear Morphology: A New Marker for Male Factor Infertility?

Infertility is a problem affecting an increasing number of couples worldwide. Currently, marker tests for male factor infertility are complex, highly technical and relatively subjective. Up to 40% of cases of male factor infertility are currently diagnosed as idiopathic therefore, there is a clear need for further research into better ways of diagnosing it. Changes in sperm telomere length have been associated with infertility and closely linked to DNA damage and fragmentation, which are also known to be related to infertility. However, telomere distribution is a parameter thus far underexplored as an infertility marker. Here, we assessed morphological parameters of sperm nuclei in fertile control and male factor infertile cohorts. In addition, we used 2D and 3D fluorescence in situ hybridization (FISH) to compare telomere distribution between these two groups. Our findings indicate that the infertile cohort sperm nuclei were, on average, 2.9% larger in area and showed subtle differences in sperm head height and width. Telomeres were mainly distributed towards the periphery of the nuclei in the control cohort, with diminishing telomere signals towards the center of the nuclei. Sperm nuclei of infertile males, however, had more telomere signals towards the center of the nuclei, a finding supported by 3D imaging. We conclude that, with further development, both morphology and telomere distribution may prove useful investigative tools in the fertility clinic.

A male germ cell assay and supporting somatic cells: its application for the detection of phase specificity of genotoxins in vitro

Male germ stem cells are responsible for transmission of genetic information to the next generation. Some chemicals exert a negative impact on male germ cells, either directly, or indirectly affecting them through their action on somatic cells. Ultimately, these effects might inhibit fertility, and may exhibit negative consequences on future offspring. Genotoxic anticancer agents may interact with DNA in germ cells potentially leading to a heritable germline mutation. Experimental information in support of this theory has not always been reproducible and suitable in vivo studies remain limited. Thus, alternative male germ cell tests, which are now able to detect phase specificity of such agents, might be used by regulatory agencies to help evaluate the potential risk of mutation. However, there is an urgent need for such approaches for identification of male reproductive genotoxins since this area has until recently been dependent on in vivo studies. Many factors drive alternative approaches, including the (1) commitment to the principles of the 3R's (Replacement, Reduction, and Refinement), (2) time-consuming nature and high cost of animal experiments, and (3) new opportunities presented by new molecular analytical assays. There is as yet currently no apparent appropriate model of full mammalian spermatogenesis in vitro, under the REACH initiative, where new tests introduced to assess genotoxicity and mutagenicity need to avoid unnecessary testing on animals. Accordingly, a battery of tests used in conjunction with the high throughput STAPUT gravity sedimentation was recently developed for purification of male germ cells to investigate genotoxicity for phase specificity in germ cells. This system might be valuable for the examination of phases previously only available in mammals with large-scale studies of germ cell genotoxicity in vivo. The aim of this review was to focus on this alternative approach and its applications as well as on chemicals of known in vivo phase specificities used during this test system development.

Double-stranded sperm DNA damage is a cause of delay in embryo development and can impair implantation rates

OBJECTIVE

To analyze the effect of single- and double-stranded sperm DNA fragmentation (ssSDF and dsSDF) on human embryo kinetics monitored under a time-lapse system.

DESIGN

Observational, double blind, prospective cohort study.

SETTING

University spin-off and private center.

PATIENT(S)

One hundred ninety-six embryos from 43 infertile couples were included prospectively.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

SsSDF and dsSDF were analyzed in the same semen sample used for intracytoplasmic sperm injection. Embryo kinetics was then monitored using time-lapse technology, and the timing of each embryo division was obtained.

RESULT(S)

When comparing embryos obtained from semen samples with low dsSDF and high dsSDF, splitting data using a statistically significant delay in high dsSDF was observed in second polar body extrusion, T4, T8, morula, and starting blastocyst and embryo implantation rates were impaired. Embryo kinetics and implantation rates are not significantly affected when high values of ssSDF are present. Different patterns of delay in embryo kinetics were observed for these different types of DNA damage: dsSDF caused a delay along all stages of embryo development; however, its major effect was observed at the second polar body extrusion and morula stages, coinciding with embryo DNA damage checkpoint activation as described before; ssSDF had its major effect at the pronucleus stage, but embryo kinetics was then restored at all following stages. The results show that dsSDF could be the main type of DNA damage that affects embryo development in intracytoplasmic sperm injection cycles, probably due to motility-based sperm selection in this assisted reproduction procedure.

CONCLUSION(S)

Double-stranded sperm DNA damage caused a delay in embryo development and impaired implantation, while single-stranded DNA damage did not significantly affect embryo kinetics and implantation.

Single and Double Strand Sperm DNA Damage: Different Reproductive Effects on Male Fertility

Reproductive diseases have become a growing worldwide problem and male factor plays an important role in the reproductive diagnosis, prognosis and design of assisted reproductive treatments. Sperm cell holds the mission of carrying the paternal genetic complement to the oocyte in order to contribute to an euploid zygote with proper DNA integrity. Sperm DNA fragmentation had been used for decades as a male fertility test, however, its usefulness have arisen multiple debates, especially around Intracytoplasmic Sperm Injection (ICSI) treatments. In the recent years, it has been described that different types of sperm DNA breaks (single and double strand DNA breaks) cause different clinical reproductive effects. On one hand, single-strand DNA breaks are present extensively as a multiple break points in all regions of the genome, are related to oxidative stress and cause a lack of clinical pregnancy or an increase of the conception time. On the other hand, double-strand DNA breaks are mainly localized and attached to the sperm nuclear matrix as a very few break points, are possibly related to a lack of DNA repair in meiosis and cause a higher risk of miscarriage, low embryo quality and higher risk of implantation failure in ICSI cycles. The present work also reviews different studies that may contribute in the understanding of sperm chromatin as well as treatments to prevent sperm DNA damage.

Gene and protein expression in the reproductive tract of Brazilian Somalis rams

Brazilian Somalis is a locally-adapted breed of rams raised in tropical climate and native pastures. The present study was conducted to evaluate gene expression and proteome of the reproductive tract of such rams. Samples were collected from testes, epididymides, seminal vesicles and bulbourethral glands of four rams. Expression of clusterin (CLU), osteopontin (OPN) and prostaglandin D2 synthase (PGDS) genes were evaluated in all samples by real-time PCR. Shotgun proteomic analysis was performed using samples from the head, corpus and cauda epididymides and from all other structures as well. Gene ontology terms and protein interactions were obtained from UniProtKB databases and MetaCore v.6.8 platform. CLU trasncripts were detected in the testes, epididymides, seminal vesicles and bulbourethral glands of the Somalis rams. The initial region and body of the epididymis had the greatest CLU expression. OPN mRNA was localized in all tissues of the ram reproductive tract. PGDS mRNA was detected in the testes and epididymides. Lable-free mass spectrometry allowed the identification of 137 proteins in all samples. Proteins of the epididymis head mainly participate in cellular processes and response to stimulus, participating in catalityc activity and binding. Proteins of epididymis body acted as regulatory proteins and in cellular processes, with binding and catalytic activity. Cauda epididymis molecules were associated with cellular processes and regulation, with binding function and catalytic activity as well. Testis proteins were mainly linked to cell processes and response to stimuli, and had catalytic function. Seminal vesicle proteins were involved in regulation and mainly with binding functions. Most bulbourethral gland proteins participated in cellular processes. The present study is the first to evaluate the proteome and gene expressions in the reproductive tract of Brazilian Somalis rams. Such pieces of information bring significant cointribution for the understanding of the reproductive physiology of locally-adapted livestock.

Epigenetic programming alterations in alligators from environmentally contaminated lakes

Previous studies examining the reproductive health of alligators in Florida lakes indicate that a variety of developmental and health impacts can be attributed to a combination of environmental quality and exposures to environmental contaminants. The majority of these environmental contaminants have been shown to disrupt normal endocrine signaling. The potential that these environmental conditions and contaminants may influence epigenetic status and correlate to the health abnormalities was investigated in the current study. The red blood cell (RBC) (erythrocyte) in the alligator is nucleated so was used as an easily purified marker cell to investigate epigenetic programming. RBCs were collected from adult male alligators captured at three sites in Florida, each characterized by varying degrees of contamination. While Lake Woodruff (WO) has remained relatively pristine, Lake Apopka (AP) and Merritt Island (MI) convey exposures to different suites of contaminants. DNA was isolated and methylated DNA immunoprecipitation (MeDIP) was used to isolate methylated DNA that was then analyzed in a competitive hybridization using a genome-wide alligator tiling array for a MeDIP-Chip analysis. Pairwise comparisons of alligators from AP and MI to WO revealed alterations in the DNA methylome. The AP vs. WO comparison identified 85 differential DNA methylation regions (DMRs) with ⩾3 adjacent oligonucleotide tiling array probes and 15,451 DMRs with a single oligo probe analysis. The MI vs. WO comparison identified 75 DMRs with the ⩾3 oligo probe and 17,411 DMRs with the single oligo probe analysis. There was negligible overlap between the DMRs identified in AP vs. WO and MI vs. WO comparisons. In both comparisons DMRs were primarily associated with CpG deserts which are regions of low CpG density (1-2CpG/100bp). Although the alligator genome is not fully annotated, gene associations were identified and correlated to major gene class functional categories and pathways of endocrine relevance. Observations demonstrate that environmental quality may be associated with epigenetic programming and health status in the alligator. The epigenetic alterations may provide biomarkers to assess the environmental exposures and health impacts on these populations of alligators.

Genomic Clustering of differential DNA methylated regions (epimutations) associated with the epigenetic transgenerational inheritance of disease and phenotypic variation

Background

A variety of environmental factors have been shown to promote the epigenetic transgenerational inheritance of disease and phenotypic variation in numerous species. Exposure to environmental factors such as toxicants can promote epigenetic changes (epimutations) involving alterations in DNA methylation to produce specific differential DNA methylation regions (DMRs). The germline (e.g. sperm) transmission of epimutations is associated with epigenetic transgenerational inheritance phenomena. The current study was designed to determine the genomic locations of environmentally induced transgenerational DMRs and assess their potential clustering.

Results

The exposure specific DMRs (epimutations) from a number of different studies were used. The clustering approach identified areas of the genome that have statistically significant over represented numbers of epimutations. The location of DMR clusters was compared to the gene clusters of differentially expressed genes found in tissues and cells associated with the transgenerational inheritance of disease. Such gene clusters, termed epigenetic control regions (ECRs), have been previously suggested to regulate gene expression in regions spanning up to 2-5 million bases. DMR clusters were often found to associate with inherent gene clusters within the genome.

Conclusion

The current study used a number of epigenetic datasets from previous studies to identify novel DMR clusters across the genome. Observations suggest these clustered DMR within an ECR may be susceptible to epigenetic reprogramming and dramatically influence genome activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2748-5) contains supplementary material, which is available to authorized users.

Environmentally induced epigenetic transgenerational inheritance of sperm epimutations promote genetic mutations

A variety of environmental factors have been shown to induce the epigenetic transgenerational inheritance of disease and phenotypic variation. This involves the germline transmission of epigenetic information between generations. Exposure specific transgenerational sperm epimutations have been previously observed. The current study was designed to investigate the potential role genetic mutations have in the process, using copy number variations (CNV). In the first (F1) generation following exposure, negligible CNV were identified; however, in the transgenerational F3 generation, a significant increase in CNV was observed in the sperm. The genome-wide locations of differential DNA methylation regions (epimutations) and genetic mutations (CNV) were investigated. Observations suggest the environmental induction of the epigenetic transgenerational inheritance of sperm epimutations promote genome instability, such that genetic CNV mutations are acquired in later generations. A combination of epigenetics and genetics is suggested to be involved in the transgenerational phenotypes. The ability of environmental factors to promote epigenetic inheritance that subsequently promotes genetic mutations is a significant advance in our understanding of how the environment impacts disease and evolution.

A simple sperm DNA toroid integrity test and risk of miscarriage

Current methods of analyzing sperm chromatin competency overlook the inner sperm compartment which is inaccessible to probes and reagents. By breaking the molecular protamine disulfide bridges, the DNA toroids are exposed to integrity analysis. The aim was to develop a simple nuclear toroid test and determine its association with fertilization, pregnancy, and miscarriage. The approach involved treating washed sperm remaining after ICSI procedures (N=35 cases) with acidified Triton X-100 and dithiothreitol (DTT) before Diff-Quik staining. Percentages of sperm with normal chromatin indicated by light-colored nuclei were assessed. The toroid integrity test showed more sperm with normal chromatin in the pregnant group (73.6±1.7%, mean±SEM) when compared with the miscarriage (51.2±6.6%) or nonpregnant groups (60.9±4.8%). Furthermore, the toroid results were correlated with ICSI fertilization (R=0.32, P=0.04) and pregnancy outcome (pregnant cases 73.6±1.7% versus nonpregnant 58.0±3.9%, P=0.001). ROC calculated cut-off was >70.0% for normal toroid integrity (sensitivity 0.98, specificity 0.33, and diagnostic accuracy 78.3%). An association between normal sperm toroid integrity and miscarriage was evident when the staining procedure included acidified detergent DTT pretreatment.

Epigenetics and the evolution of Darwin's Finches

The prevailing theory for the molecular basis of evolution involves genetic mutations that ultimately generate the heritable phenotypic variation on which natural selection acts. However, epigenetic transgenerational inheritance of phenotypic variation may also play an important role in evolutionary change. A growing number of studies have demonstrated the presence of epigenetic inheritance in a variety of different organisms that can persist for hundreds of generations. The possibility that epigenetic changes can accumulate over longer periods of evolutionary time has seldom been tested empirically. This study was designed to compare epigenetic changes among several closely related species of Darwin's finches, a well-known example of adaptive radiation. Erythrocyte DNA was obtained from five species of sympatric Darwin's finches that vary in phylogenetic relatedness. Genome-wide alterations in genetic mutations using copy number variation (CNV) were compared with epigenetic alterations associated with differential DNA methylation regions (epimutations). Epimutations were more common than genetic CNV mutations among the five species; furthermore, the number of epimutations increased monotonically with phylogenetic distance. Interestingly, the number of genetic CNV mutations did not consistently increase with phylogenetic distance. The number, chromosomal locations, regional clustering, and lack of overlap of epimutations and genetic mutations suggest that epigenetic changes are distinct and that they correlate with the evolutionary history of Darwin's finches. The potential functional significance of the epimutations was explored by comparing their locations on the genome to the location of evolutionarily important genes and cellular pathways in birds. Specific epimutations were associated with genes related to the bone morphogenic protein, toll receptor, and melanogenesis signaling pathways. Species-specific epimutations were significantly overrepresented in these pathways. As environmental factors are known to result in heritable changes in the epigenome, it is possible that epigenetic changes contribute to the molecular basis of the evolution of Darwin's finches.

Pesticide methoxychlor promotes the epigenetic transgenerational inheritance of adult-onset disease through the female germline

Environmental compounds including fungicides, plastics, pesticides, dioxin and hydrocarbons can promote the epigenetic transgenerational inheritance of adult-onset disease in future generation progeny following ancestral exposure during the critical period of fetal gonadal sex determination. This study examined the actions of the pesticide methoxychlor to promote the epigenetic transgenerational inheritance of adult-onset disease and associated differential DNA methylation regions (i.e. epimutations) in sperm. Gestating F0 generation female rats were transiently exposed to methoxychlor during fetal gonadal development (gestation days 8 to 14) and then adult-onset disease was evaluated in adult F1 and F3 (great-grand offspring) generation progeny for control (vehicle exposed) and methoxychlor lineage offspring. There were increases in the incidence of kidney disease, ovary disease, and obesity in the methoxychlor lineage animals. In females and males the incidence of disease increased in both the F1 and the F3 generations and the incidence of multiple disease increased in the F3 generation. There was increased disease incidence in F4 generation reverse outcross (female) offspring indicating disease transmission was primarily transmitted through the female germline. Analysis of the F3 generation sperm epigenome of the methoxychlor lineage males identified differentially DNA methylated regions (DMR) termed epimutations in a genome-wide gene promoters analysis. These epimutations were found to be methoxychlor exposure specific in comparison with other exposure specific sperm epimutation signatures. Observations indicate that the pesticide methoxychlor has the potential to promote the epigenetic transgenerational inheritance of disease and the sperm epimutations appear to provide exposure specific epigenetic biomarkers for transgenerational disease and ancestral environmental exposures.

Analysis of the sperm head protein profiles in fertile men: consistency across time in the levels of expression of heat shock proteins and peroxiredoxins

We investigated the identity and quantitative variations of proteins extracted from human sperm heads using a label-free Gel-MS approach. Sperm samples were obtained from three men with high sperm counts at three different time points. This design allowed us to analyse intra-individual and inter-individual variations of the human sperm head proteome. Each time point was analyzed in triplicate to minimize any background artifactual effects of the methodology on the variation analyses. Intra-individual analysis using the spectral counting method revealed that the expression levels of 90% of the common proteins identified in three samples collected at various time-points, separated by several months, had a coefficient of variation of less than 0.5 for each man. Across individuals, the expression level of more than 80% of the proteins had a CV under 0.7. Interestingly, 83 common proteins were found within the core proteome as defined by the intra- and inter-variation analyses set criteria (CV<0.7). Some of these uniformly expressed proteins were chaperones, peroxiredoxins, isomerases, and cytoskeletal proteins. Although there is a significant level of inter-individual variation in the protein profiles of human sperm heads even in a well-defined group of men with high sperm counts, the consistent expression levels of a wide range of proteins points to their essential role during spermatogenesis.

Ancestral dichlorodiphenyltrichloroethane (DDT) exposure promotes epigenetic transgenerational inheritance of obesity

BACKGROUND

Ancestral environmental exposures to a variety of environmental factors and toxicants have been shown to promote the epigenetic transgenerational inheritance of adult onset disease. The present work examined the potential transgenerational actions of the insecticide dichlorodiphenyltrichloroethane (DDT) on obesity and associated disease.

METHODS

Outbred gestating female rats were transiently exposed to a vehicle control or DDT and the F1 generation offspring bred to generate the F2 generation and F2 generation bred to generate the F3 generation. The F1 and F3 generation control and DDT lineage rats were aged and various pathologies investigated. The F3 generation male sperm were collected to investigate methylation between the control and DDT lineage male sperm.

RESULTS

The F1 generation offspring (directly exposed as a fetus) derived from the F0 generation exposed gestating female rats were not found to develop obesity. The F1 generation DDT lineage animals did develop kidney disease, prostate disease, ovary disease and tumor development as adults. Interestingly, the F3 generation (great grand-offspring) had over 50% of males and females develop obesity. Several transgenerational diseases previously shown to be associated with metabolic syndrome and obesity were observed in the testis, ovary and kidney. The transgenerational transmission of disease was through both female (egg) and male (sperm) germlines. F3 generation sperm epimutations, differential DNA methylation regions (DMR), induced by DDT were identified. A number of the genes associated with the DMR have previously been shown to be associated with obesity.

CONCLUSIONS

Observations indicate ancestral exposure to DDT can promote obesity and associated disease transgenerationally. The etiology of disease such as obesity may be in part due to environmentally induced epigenetic transgenerational inheritance.

Hydrocarbons (jet fuel JP-8) induce epigenetic transgenerational inheritance of obesity, reproductive disease and sperm epimutations

Environmental compounds have been shown to promote epigenetic transgenerational inheritance of disease. The current study was designed to determine if a hydrocarbon mixture involving jet fuel (JP-8) promotes epigenetic transgenerational inheritance of disease. Gestating F0 generation female rats were transiently exposed during the fetal gonadal development period. The direct exposure F1 generation had an increased incidence of kidney abnormalities in both females and males, prostate and pubertal abnormalities in males, and primordial follicle loss and polycystic ovarian disease in females. The first transgenerational generation is the F3 generation, and the jet fuel lineage had an increased incidence of primordial follicle loss and polycystic ovarian disease in females, and obesity in both females and males. Analysis of the jet fuel lineage F3 generation sperm epigenome identified 33 differential DNA methylation regions, termed epimutations. Observations demonstrate hydrocarbons can promote epigenetic transgenerational inheritance of disease and sperm epimutations, potential biomarkers for ancestral exposures.

Plastics derived endocrine disruptors (BPA, DEHP and DBP) induce epigenetic transgenerational inheritance of obesity, reproductive disease and sperm epimutations

Environmental compounds are known to promote epigenetic transgenerational inheritance of adult onset disease in subsequent generations (F1–F3) following ancestral exposure during fetal gonadal sex determination. The current study was designed to determine if a mixture of plastic derived endocrine disruptor compounds bisphenol-A (BPA), bis(2-ethylhexyl)phthalate (DEHP) and dibutyl phthalate (DBP) at two different doses promoted epigenetic transgenerational inheritance of adult onset disease and associated DNA methylation epimutations in sperm. Gestating F0 generation females were exposed to either the “plastics” or “lower dose plastics” mixture during embryonic days 8 to 14 of gonadal sex determination and the incidence of adult onset disease was evaluated in F1 and F3 generation rats. There were significant increases in the incidence of total disease/abnormalities in F1 and F3 generation male and female animals from plastics lineages. Pubertal abnormalities, testis disease, obesity, and ovarian disease (primary ovarian insufficiency and polycystic ovaries) were increased in the F3 generation animals. Kidney and prostate disease were only observed in the direct fetally exposed F1 generation plastic lineage animals. Analysis of the plastics lineage F3 generation sperm epigenome previously identified 197 differential DNA methylation regions (DMR) in gene promoters, termed epimutations. A number of these transgenerational DMR form a unique direct connection gene network and have previously been shown to correlate with the pathologies identified. Observations demonstrate that a mixture of plastic derived compounds, BPA and phthalates, can promote epigenetic transgenerational inheritance of adult onset disease. The sperm DMR provide potential epigenetic biomarkers for transgenerational disease and/or ancestral environmental exposures.

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.

Analysing the sperm epigenome: roles in early embryogenesis and assisted reproduction

An understanding of the epigenetic mechanisms involved in sperm production and their impact on the differentiating embryo is essential if we are to optimize fertilization and assisted reproduction techniques in the future. Male germ cells are unique in terms of size, robustness, and chromatin structure, which is highly condensed owing to the replacement of most histones by protamines. Analysis of sperm epigenetics requires specific techniques that enable the isolation of high quality chromatin and associated nucleic acids. Histone modification, DNA methylation and noncoding RNAs have important, but so far underestimated, roles in the production of fertile sperm. Aberrations in these epigenetic processes have detrimental consequences for both early embryo development and assisted reproductive technology. Emerging computational techniques are likely to improve our understanding of chromatin dynamics in the future.

Dioxin (TCDD) induces epigenetic transgenerational inheritance of adult onset disease and sperm epimutations

Environmental compounds can promote epigenetic transgenerational inheritance of adult-onset disease in subsequent generations following ancestral exposure during fetal gonadal sex determination. The current study examined the ability of dioxin (2,3,7,8-tetrachlorodibenzo[p]dioxin, TCDD) to promote epigenetic transgenerational inheritance of disease and DNA methylation epimutations in sperm. Gestating F0 generation females were exposed to dioxin during fetal day 8 to 14 and adult-onset disease was evaluated in F1 and F3 generation rats. The incidences of total disease and multiple disease increased in F1 and F3 generations. Prostate disease, ovarian primordial follicle loss and polycystic ovary disease were increased in F1 generation dioxin lineage. Kidney disease in males, pubertal abnormalities in females, ovarian primordial follicle loss and polycystic ovary disease were increased in F3 generation dioxin lineage animals. Analysis of the F3 generation sperm epigenome identified 50 differentially DNA methylated regions (DMR) in gene promoters. These DMR provide potential epigenetic biomarkers for transgenerational disease and ancestral environmental exposures. Observations demonstrate dioxin exposure of a gestating female promotes epigenetic transgenerational inheritance of adult onset disease and sperm epimutations.

Pesticide and insect repellent mixture (permethrin and DEET) induces epigenetic transgenerational inheritance of disease and sperm epimutations

Environmental compounds are known to promote epigenetic transgenerational inheritance of disease. The current study was designed to determine if a "pesticide mixture" (pesticide permethrin and insect repellent N,N-diethyl-meta-toluamide, DEET) promotes epigenetic transgenerational inheritance of disease and associated DNA methylation epimutations in sperm. Gestating F0 generation female rats were exposed during fetal gonadal sex determination and the incidence of disease evaluated in F1 and F3 generations. There were significant increases in the incidence of total diseases in animals from pesticide lineage F1 and F3 generation animals. Pubertal abnormalities, testis disease, and ovarian disease (primordial follicle loss and polycystic ovarian disease) were increased in F3 generation animals. Analysis of the pesticide lineage F3 generation sperm epigenome identified 363 differential DNA methylation regions (DMR) termed epimutations. Observations demonstrate that a pesticide mixture (permethrin and DEET) can promote epigenetic transgenerational inheritance of adult onset disease and potential sperm epigenetic biomarkers for ancestral environmental exposures.

Defective histone H3K27 trimethylation modification in embryos derived from heated mouse sperm

The mouse sperm genome is resistant to in vitro heat treatment, and embryos derived from heated sperm can support full-term embryonic development, but the blastocyst rate and implantation rate are lower compared to embryos derived from fresh sperm. In the present study, the patterns of DNA methylation, histone H4K12 (ACH4K12) acetylation, H3K9 trimethylation (H3K9-TriM), and H3K27 trimethylation (H3K27-TriM) in preimplantation embryos derived from 65 °C-heated sperm were investigated. Although no evident changes in global DNA methylation, histone H4K12 (ACH4K12) acetylation, and H3K9 trimethylation (H3K9-TriM) were found, significantly lower levels of H3K27-TriM, which was thought to be one of the reasons for low efficiency of mouse cloning, were found in the inner cell mass of heated-sperm derived blastocysts. Thus, defective modification of H3K27-TriM might contribute to compromised development of embryos derived from heated sperm.

Transgenerational actions of environmental compounds on reproductive disease and identification of epigenetic biomarkers of ancestral exposures

Environmental factors during fetal development can induce a permanent epigenetic change in the germ line (sperm) that then transmits epigenetic transgenerational inheritance of adult-onset disease in the absence of any subsequent exposure. The epigenetic transgenerational actions of various environmental compounds and relevant mixtures were investigated with the use of a pesticide mixture (permethrin and insect repellant DEET), a plastic mixture (bisphenol A and phthalates), dioxin (TCDD) and a hydrocarbon mixture (jet fuel, JP8). After transient exposure of F0 gestating female rats during the period of embryonic gonadal sex determination, the subsequent F1-F3 generations were obtained in the absence of any environmental exposure. The effects on the F1, F2 and F3 generations pubertal onset and gonadal function were assessed. The plastics, dioxin and jet fuel were found to promote early-onset female puberty transgenerationally (F3 generation). Spermatogenic cell apoptosis was affected transgenerationally. Ovarian primordial follicle pool size was significantly decreased with all treatments transgenerationally. Differential DNA methylation of the F3 generation sperm promoter epigenome was examined. Differential DNA methylation regions (DMR) were identified in the sperm of all exposure lineage males and found to be consistent within a specific exposure lineage, but different between the exposures. Several genomic features of the DMR, such as low density CpG content, were identified. Exposure-specific epigenetic biomarkers were identified that may allow for the assessment of ancestral environmental exposures associated with adult onset disease.

Nuclear organisation of sperm remains remarkably unaffected in the presence of defective spermatogenesis

Organisation of chromosome territories in interphase nuclei has been studied in many systems and positional alterations have been associated with disease phenotypes (e.g. laminopathies, cancer) in somatic cells. Altered nuclear organisation is also reported in developmental processes such as mammalian spermatogenesis where a "chromocentre" model is proposed with the centromeres and sex chromosomes repositioning to the nuclear centre. The purpose of this study was to test the hypothesis that alterations in nuclear organisation of human spermatozoa are associated with defects upstream in spermatogenesis (as manifest in certain infertility phenotypes). The nuclear address of (peri-) centromeric loci for 18 chromosomes (1-4, 6-12, 15-18, 20, X and Y) was assayed in 20 males using established algorithms for 3D extrapolations of 2D data. The control group comprised 10 fertile sperm donors while the test group was 10 patients with severely compromised semen parameters including high sperm aneuploidy. All loci examined in the control group adopted defined, interior positions thus providing supporting evidence for the presence of a chromocentre and interior sex chromosome territories. In the test group however there were subtle alterations in the nuclear address for certain centromeres in individual patients and, when all patient results were pooled, some different nuclear addresses were observed for chromosomes 3, 6, 12 and 18. Considering the extensive impairment of spermatogenesis in the test group (evidenced by compromised semen parameters and increased chromosome abnormalities), the observed differences in nuclear organisation for centromeric loci compared to the controls were modest. A defined pattern of nuclear reorganisation of centromeric loci in sperm heads therefore appears to be a remarkably robust process, even if spermatogenesis is severely compromised.

Sperm DNA integrity assays: diagnostic and prognostic challenges and implications in management of infertility

Sperm is not a simple carrier of paternal genetic information but its role extends clearly beyond fertilization. Integrity of sperm genome is an essential pre-requisite for birth of healthy offspring and evaluation of sperm should entail DNA integrity analysis. DNA integrity analysis is a better diagnostic and prognostic marker of sperm reproductive potential. Conventional semen analysis emphasizes on sperm concentration, viability, motility and morphology and has been proven to be a poor indicator of reproductive potential and pregnancy outcome. To overcome the drawbacks associated with conventional semen analysis more useful fertility tests and molecular biomarkers have been explored. Among the different tests which have evolved for assessing the sperm reproductive potential, tests for sperm DNA quality are most promising. Sperm DNA damage has been closely associated with numerous indicators of reproductive health including fertilization, embryo quality, implantation, spontaneous abortion, congenital malformations and childhood diseases. It therefore has great potential as a prognostic test for both in vitro and in vivo conception. This review presents an updated account of tests that have better diagnostic and prognostic implications in the evaluation of sperm DNA damage. The basic principles, outline of methodology, advantage, disadvantage, clinical significance of each technique and implications of these tests have been discussed. The logistics of each test with respect to available resources and equipment in an andrology laboratory, the feasibility of performing these tests in routine diagnostic workup of infertile men and the opportunities and challenges provided by DNA testing in male fertility determination are also presented.

The sperm nucleus: chromatin, RNA, and the nuclear matrix

Within the sperm nucleus, the paternal genome remains functionally inert and protected following protamination. This is marked by a structural morphogenesis that is heralded by a striking reduction in nuclear volume. Despite these changes, both human and mouse spermatozoa maintain low levels of nucleosomes that appear non-randomly distributed throughout the genome. These regions may be necessary for organizing higher order genomic structure through interactions with the nuclear matrix. The promoters of this transcriptionally quiescent genome are differentially marked by modified histones that may poise downstream epigenetic effects. This notion is supported by increasing evidence that the embryo inherits these differing levels of chromatin organization. In concert with the suite of RNAs retained in the mature sperm, they may synergistically interact to direct early embryonic gene expression. Irrespective, these features reflect the transcriptional history of spermatogenic differentiation. As such, they may soon be utilized as clinical markers of male fertility. In this review, we explore and discuss how this may be orchestrated.

Male fertility, chromosome abnormalities, and nuclear organization

Numerous studies have implicated the role of gross genomic rearrangements in male infertility, e.g., constitutional aneuploidy, translocations, inversions, Y chromosome deletions, elevated sperm disomy, and DNA damage. The primary purpose of this paper is to review male fertility studies associated with such abnormalities. In addition, we speculate whether altered nuclear organization, another chromosomal/whole genome-associated phenomenon, is also concomitant with male factor infertility. Nuclear organization has been studied in a range of systems and implicated in several diseases. For many applications the measurement of the relative position of chromosome territories is sufficient to determine patterns of nuclear organization. Initial evidence has suggested that, unlike in the more usual 'size-related' or 'gene density-related' models, mammalian (including human) sperm heads display a highly organized pattern including a chromocenter with the centromeres located to the center of the nucleus and the telomeres near the periphery. More recent evidence, however, suggests there may be size- and gene density-related components to nuclear organization in sperm. It seems reasonable to hypothesize therefore that alterations in this pattern may be associated with male factor infertility. A small handful of studies have addressed this issue; however, to date it remains an exciting avenue for future research with possible implications for diagnosis and therapy.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 2: changes in spermatid organelles associated with development of spermatozoa

Spermiogenesis is a long process whereby haploid spermatids derived from the meiotic divisions of spermatocytes undergo metamorphosis into spermatozoa. It is subdivided into distinct steps with 19 being identified in rats, 16 in mouse and 8 in humans. Spermiogenesis extends over 22.7 days in rats and 21.6 days in humans. In this part, we review several key events that take place during the development of spermatids from a structural and functional point of view. During early spermiogenesis, the Golgi apparatus forms the acrosome, a lysosome-like membrane bound organelle involved in fertilization. The endoplasmic reticulum undergoes several topographical and structural modifications including the formation of the radial body and annulate lamellae. The chromatoid body is fully developed and undergoes structural and functional modifications at this time. It is suspected to be involved in RNA storing and processing. The shape of the spermatid head undergoes extensive structural changes that are species-specific, and the nuclear chromatin becomes compacted to accommodate the stream-lined appearance of the sperm head. Microtubules become organized to form a curtain or manchette that associates with spermatids at specific steps of their development. It is involved in maintenance of the sperm head shape and trafficking of proteins in the spermatid cytoplasm. During spermiogenesis, many genes/proteins have been implicated in the diverse dynamic events occurring at this time of development of germ cells and the absence of some of these have been shown to result in subfertility or infertility.

Sperm-borne protein, PAWP, initiates zygotic development in Xenopus laevis by eliciting intracellular calcium release

We previously reported postacrosomal sheath WW domain binding protein (PAWP) as a candidate sperm borne, oocyte-activating factor. PAWP enters the oocyte during fertilization and induces oocyte activation events including meiotic resumption, pronuclear formation, and egg cleavage. However, in order to provide proof that PAWP is a primary initiator of zygotic development it is imperative to show that PAWP initiates intracellular calcium signaling, which is considered essential for oocyte activation. Utilizing Xenopus laevis as our model, we injected recombinant PAWP or Xenopus sperm into metaphase II-arrested oocytes and observed a significant rise in intracellular calcium levels over controls. Concurring intensities and durations of PAWP and sperm-induced calcium waves, detected by infrared two-photon laser-scanning fluorescence microscopy, were prevented by coinjection of a competitive PPGY-containing peptide derived from PAWP but not by the point-mutated form of this peptide. This study also correlates PAWP and sperm-induced calcium release with meiotic resumption in Xenopus. The similar mode of oocyte activation, and the ability of the competitive peptide in blocking both sperm- and PAWP-induced calcium release, provide evidence for the first time that sperm-anchored PAWP is a primary initiator of zygotic development.

Paternal exposure to cyclophosphamide affects the progression of sperm chromatin decondensation and activates a DNA damage response in the prepronuclear rat zygote

Spermatozoon decondensation in the zygote leads to the initiation of chromatin remodeling during which protamines are removed and replaced with maternal histones. We hypothesize that damage to male germ cells induced by paternal exposure to cyclophosphamide may alter the timing of spermatozoal decondensation and the pattern of chromatin remodeling in the prepronuclear rat zygote. A specific order of sperm decondensation was observed, starting at the posterior end, proceeding to the ventral sides, followed by the tip, and finally the midbody region of the sperm head nucleus; subgroups of partially decondensed type a sperm nuclei were defined as types a1, a2, a3, and a4. Based on their frequencies relative to controls, paternal exposure to cyclophosphamide accelerated the timing of spermatozoal decondensation. Two distinct patterns of chromatin remodeling were observed for totally decondensed (type b) and recondensing (type c) sperm nuclei: H4K12ac showed a homogenous staining, whereas H3S10ph displayed a ring-like staining around the sperm nucleus; the distribution of these posttranslationally modified histones was not affected by cyclophosphamide exposure. In contrast, paternal cyclophosphamide treatment increased the number of gammaH2AX foci found in decondensing sperm nuclei. Small foci were significantly increased in type a2 and a3 nuclei, whereas a significant increase in the numbers of large foci was found in type b and c nuclei. This increase in gammaH2AX foci in the decondensing male genome suggests that damage recognition and repair pathways are initiated in prepronuclear rat zygotes. Thus, exposure of male rats to chronic low doses of cyclophosphamide accelerates spermatozoal decondensation and leads to the activation of gammaH2AX recognition of DNA damage in the male genome of the prepronuclear zygote.

Paternal DNA packaging in spermatozoa: more than the sum of its parts? DNA, histones, protamines and epigenetics

Haploid male germ cells package their DNA into a volume that is typically 10% or less that of a somatic cell nucleus. To achieve this remarkable level of compaction, spermatozoa replace most of their histones with smaller, highly basic arginine and (in eutherians) cysteine rich protamines. One reason for such a high level of compaction is that it may help optimise nuclear shape and hence support the gametes' swimming ability for the long journey across the female reproductive tract to the oocyte. Super-compaction of the genome may confer additional protection from the effects of genotoxic factors. However, many species including the human retain a fraction of their chromatin in the more relaxed nucleosomal configuration that appears to run counter to the ergonomic, toroidal and repackaging of sperm DNA. Recent research suggests that the composition of this 'residual' nucleosomal compartment, a generally overlooked feature of the male gamete, is far more significant and important than previously thought. In this respect, the transport and incorporation of modified paternal histones by the spermatozoon to the zygote has been demonstrated and indicates another potential paternal effect in the epigenetic reprogramming of the zygote following fertilisation that is independent of imprinting status. In this review, the most recent research into mammalian spermatozoal chromatin composition is discussed alongside evidence for conserved, non-randomly located nucleosomal domains in spermatozoal nuclei, all supporting the hypothesis that the spermatozoon delivers a novel epigenetic signature to the egg that may be crucial for normal development. We also provide some thoughts on why this signature may be required in early embryogenesis.

Memoirs of an insult: sperm as a possible source of transgenerational epimutations and genetic instability

Male transgenerational epigenetic effects have been discovered in the discipline of mouse radiation genetics, using genetic and non-genetic readouts. The mechanism to explain the origin of the transmission of epigenetic and genetic instability is still unknown. In a search for a hypothesis that could satisfy the data, we propose that regulation of chromosome structure in the germline, by the occupancy of matrix/scaffold associated regions, contains molecular memory function. The male germline is strikingly dynamic as to chromatin organization. This could explain why experience of irradiation stress leaves a persistent mark in the male germline only. To be installed, such memory requires both S-phase and chromatin reorganization during spermatogenesis and in the zygote, that likely also involves reorganization of loop domains. By this reorganization, another layer of information is added, needed to accommodate early embryonic development. Observations point at the involvement of DNA repair as inducer of transgenerational epigenetic modulation. Nuclear structure, chromatin composition and loop domain organization are aspects of human sperm variability that in many cases of assisted reproduction is increased due to inclusion of more incompletely differentiated/maturated sperm nuclei. Adjustment of loop domains in early embryo development can be anticipated and zygotic and cleavage stage S-phase repair activity will have to deal with potential paternal DNA lesions. Therefore, by changing male nucleus structure due to reproduction from impaired spermatogenesis, the transgenerational information content could be changed as well. We discuss aspects of male reproductive performance in the context of this hypothesis.

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.

Toxicants and human sperm chromatin integrity

The integrity of the paternal genome is essential as the spermatozoon can bring genetic damage into the oocyte at fertilization and contribute to the development of abnormal pregnancy outcome. During the past two decades, many assays have been developed to measure sperm DNA strand breaks, chromatin structure and compaction and assess the proteins associated with the DNA, as well as epigenetic modifications. Using these assays, it has been shown that exposure to physical agents or chemicals, including therapeutic drugs and environmental toxicants, can affect the integrity of sperm chromatin, inducing structural, genetic and/or epigenetic abnormalities. The mechanisms by which such damage is triggered are still largely unresolved and the susceptibility of each individual will depend on their genetic background, lifestyle and exposure to various insults. Depending on the nature of the chemicals, they may directly target the DNA, induce an oxidative stress, or modify the epigenetic elements. The significance of measuring the sperm chromatin integrity comes from the fact that this end-point correlates well with the low IVF and ICSI outcomes, and idiopathic infertility. Nevertheless, it is hard to establish a direct link between the paternal sperm chromatin integrity and the health of the future generations. Thus, it seems essential to undertake studies that will resolve the impact of chemical and environmental factors on chromatin structure and epigenetic components of human spermatozoa and to elucidate what sperm nuclear end-points are predictors of the quality of progeny outcome.

Sperm chromatin-induced ectopic polar body extrusion in mouse eggs after ICSI and delayed egg activation

Meiotic chromosomes in an oocyte are not only a maternal genome carrier but also provide a positional signal to induce cortical polarization and define asymmetric meiotic division of the oocyte, resulting in polar body extrusion and haploidization of the maternal genome. The meiotic chromosomes play dual function in determination of meiosis: 1) organizing a bipolar spindle formation and 2) inducing cortical polarization and assembly of a distinct cortical cytoskeleton structure in the overlying cortex for polar body extrusion. At fertilization, a sperm brings exogenous paternal chromatin into the egg, which induces ectopic cortical polarization at the sperm entry site and leads to a cone formation, known as fertilization cone. Here we show that the sperm chromatin-induced fertilization cone formation is an abortive polar body extrusion due to lack of spindle induction by the sperm chromatin during fertilization. If experimentally manipulating the fertilization process to allow sperm chromatin to induce both cortical polarization and spindle formation, the fertilization cone can be converted into polar body extrusion. This suggests that sperm chromatin is also able to induce polar body extrusion, like its maternal counterpart. The usually observed cone formation instead of ectopic polar body extrusion induced by sperm chromatin during fertilization is due to special sperm chromatin compaction which restrains it from rapid spindle induction and therefore provides a protective mechanism to prevent a possible paternal genome loss during ectopic polar body extrusion.

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.

Production of normal mice from spermatozoa denatured with high alkali treatment before ICSI

In mammals, ICSI is now a very important tool for both assisted reproductive technology and studying the mechanisms of fertilization. In the latter experiments, it is important to use spermatozoa that have lost their oocyte activation capacity but still retain their developmental potential. In this study, we used high-concentration NaOH to remove oocyte activation potential from spermatozoa, and examined whether normal offspring could be generated from these spermatozoa after ICSI. The spermatozoa were treated with different concentrations of NaOH (1–100 mM) for 1 h and then neutralized with equal amounts of same concentration of HCl. In 10 mM NaOH-treated spermatozoa, the cell membrane was broken and most of them failed to activate oocytes after their injection into the oocytes. However, these spermatozoa did not show strong damage, and after artificial activation with SrCl2, all of the zygotes were judged as normal by immunostaining to check the methylation status of histone H3 lysine 9, low chromosome damage by karyotype assay and staining with DNA double-strand breaks marker, γH2AX. Moreover, after transferring those embryos into recipient females, 106 (36.7%) live and healthy offspring were delivered, which is similar to the rate in the fresh control group. By contrast, spermatozoa treated with lower NaOH concentrations retained their oocyte activation capacity and those treated with higher concentrations lost their developmental potential. This suggests that 10 mM NaOH for 1 h is the best treatment to completely destroy the cell membrane and activation capacity of spermatozoa without injuring their developmental potential.

RNA polymerase II interacts with the Hspa1b promoter in mouse epididymal spermatozoa

The Hspa1b (Hsp70.1) gene is one of the first genes expressed after fertilization, with expression occurring during the minor zygotic genome activation (ZGA) in the absence of stress. This expression can take place in the male pronucleus as early as the one-cell stage of embryogenesis. The importance of HSPA1B for embryonic viability during times of stress is supported by studies showing that depletion of this protein results in a significant reduction in embryos developing to the blastocyte stage. Recently, we have begun addressing the mechanism responsible for allowing expression of Hspa1b during the minor ZGA and found that heat shock transcription factor (HSF) 1 and 2 bind the Hspa1b promoter during late spermatogenesis. In this report, we have extended those studies using western blots and chromatin immunoprecipitation assays and found that RNA polymerase II (Pol II) is present in epididymal spermatozoa and bound to the Hspa1b promoter. These present results, in addition to our previous results, support a model in which the binding of HSF1, HSF2, SP1, and Pol II to the promoter of Hspa1b would allow the rapid formation of a transcription-competent state during the minor ZGA, thereby allowing Hspa1b expression.

Paternal contributions: new functional insights for spermatozoal RNA

Whereas the presence of RNA in mature ejaculate spermatozoa is now established, its functional significance, if any, is still a matter of debate. This reflects the accepted description that spermatozoa are highly differentiated, specialized cells of minimal cytoplasm and compacted nucleus that are transcriptionally inactive. A significant proportion of the RNA required for the later, haploid stages of terminal spermatogenic differentiation (spermiogenesis) is synthesized prior to transcriptional arrest then stably stored until its translation during spermiogenesis. Spermatozoal RNAs, including messenger RNAs (mRNAs) are therefore considered to be stored remnants. Any role in fertilization and early development has, until recently, seemed unlikely, since the oocyte contains large stores of maternal mRNAs known to be required for early embryonic development prior to zygotic genome activation. Although the spermatozoon can deliver its RNA to the oocyte at fertilization, it has been generally assumed that compared to the oocyte RNA reserve, the spermatozoan payload is too small to be functional in embryo development. However, the debate continues as recent studies suggest that in specific instances sperm RNA is functional. This review presents and discusses the functional significance of spermatozoal RNA in relation to some recent advances in the field.