Sperm chromatin remodeling after intracytoplasmic sperm injection differs from that of in vitro fertilization

Effect of chemical activators after intracytoplasmic sperm injection (ICSI) on embryo development in alpacas

Low motility and low sperm concentration are characteristics of alpaca semen. Thus, the intracytoplasmic sperm injection (ICSI) technique represents an alternative to improve the reproductive capacity of the male. However, the effect of post-ICSI activation in alpaca is not yet known. The aim of the present study was to compare the effect of chemical activators on alpaca embryo development after ICSI. Alpaca ovaries were collected from a local slaughterhouse and transported to the laboratory. Category I, II and III oocytes were matured for 30 h at 38.5 °C. After ICSI, injected oocytes were randomly divided and activated as follows: i) 5 μM ionomycin for 5 min, ii) 7% ethanol for 4 min, iii) 5 μM ionomycin for 5 min, window period 3 h plus 7% ethanol for 4 min, iv) 5 μM ionomycin for 5 min, window period 3 h, a second ionomycin treatment for 5 min, followed by 1.9 mM 6-DMAP for 3 h, v) 10 mM SrCl2 for 3 h. Culture was carried out for 5 days in SOFaa at 38.5 °C. The cleavage rate was the lowest in the SrCl2 group, morula development was the lowest in the SrCl2 and without activation groups, and blastocyst stage was not different between groups (P<0.05). The rates with SrCl2 were lower in total embryos produced, whereas in transferable embryos they were lower with 2Io/6-DMAP and with SrCl2 (P<0.05). In conclusion, alpaca oocyte activation is more efficient with ionomycin and ethanol to produce transferable embryos.

Effects of triton X-100 pretreatment of lyophilized and frozen-thawed ram sperm on preimplantation embryo developmental competence

In this study, it was aimed to determine the effect of destruction of lyophilized and frozen-thawed ram sperm plasma and acrosomal membrane on development of embryos produced by intracytoplasmic sperm injection (ICSI). Semen samples were divided into two groups for lyophilization (L) and freezing (F). For the removal of the plasma membrane, L and F groups were incubated with Triton X-100 (LTX-100 and FTX-100, respectively). Integrities of the plasma membrane, acrosome and chromatin structure were evaluated. Oocytes were injected with these sperm groups. Although no plasma membrane and acrosome integrities of the L (0.0%) group were detected, the plasma membrane integrity of the F group (69.4%) was significantly higher than the FTX-100 group (23.6%) (p < 0.05). The acrosome integrity of the FTX-100 group (3.80%) was significantly lower than the F group (55.6%) (p < 0.05). The chromatin integrities of L and F groups were higher than the Triton X-100 treated groups (p < 0.05). ICSIs with L, LTX-100, F and FTX-100 sperm were produced similar cleavage and blastocyst rates. In conclusion, data presented here confirm that ram spermatozoa can effectively be lyophilized and injected into oocytes for initiation of embryonic development and Triton X-100 pretreatment is not necessary while using lyophilized and frozen semen.

The Sperm Small RNA Transcriptome: Implications beyond Reproductive Disorder

Apart from the paternal half of the genetic material, the male gamete carries assorted epigenetic marks for optimal fertilization and the developmental trajectory for the early embryo. Recent works showed dynamic changes in small noncoding RNA (sncRNA) in spermatozoa as they transit through the testicular environment to the epididymal segments. Studies demonstrated the changes to be mediated by epididymosomes during the transit through the adluminal duct in the epididymis, and the changes in sperm sncRNA content stemmed from environmental insults significantly altering the early embryo development and predisposing the offspring to metabolic disorders. Here, we review the current knowledge on the establishment of the sperm sncRNA transcriptome and their role in male-factor infertility, evidence of altered offspring health in response to the paternal life experiences through sperm sncRNA species and, finally, their implications in assisted reproductive technology in terms of epigenetic inheritance.

Genetically-biased fertilization in APOBEC1 complementation factor (A1cf) mutant mice

Meiosis, recombination, and gametogenesis normally ensure that gametes combine randomly. But in exceptional cases, fertilization depends on the genetics of gametes from both females and males. A key question is whether their non-random union results from factors intrinsic to oocytes and sperm, or from their interactions with conditions in the reproductive tracts. To address this question, we used in vitro fertilization (IVF) with a mutant and wild-type allele of the A1cf (APOBEC1 complementation factor) gene in mice that are otherwise genetically identical. We observed strong distortion in favor of mutant heterozygotes showing that bias depends on the genetics of oocyte and sperm, and that any environmental input is modest. To search for the potential mechanism of the 'biased fertilization', we analyzed the existing transcriptome data and demonstrated that localization of A1cf transcripts and its candidate mRNA targets is restricted to the spermatids in which they originate, and that these transcripts are enriched for functions related to meiosis, fertilization, RNA stability, translation, and mitochondria. We propose that failure to sequester mRNA targets in A1cf mutant heterozygotes leads to functional differences among spermatids, thereby providing an opportunity for selection among haploid gametes. The study adds to the understanding of the gamete interaction at fertilization. Discovery that bias is evident with IVF provides a new venue for future explorations of preference among genetically distinct gametes at fertilization for A1cf and other genes that display significant departure of Mendelian inheritance.

Functional Aspects of Sperm Chromatin Organization

Sperm nuclei present a highly organized and condensed chromatin due to the interchange of histones by protamines during spermiogenesis. This high DNA condensation leads to almost inert chromatin, with the impossibility of conducting gene transcription as in most other somatic cells. The major chromosomal structure responsible for DNA condensation is the formation of protamine-DNA toroids containing 25-50 kilobases of DNA. These toroids are connected by toroid linker regions (TLR), which attach them to the nuclear matrix, as matrix attachment regions (MAR) do in somatic cells. Despite this high degree of condensation, evidence shows that sperm chromatin contains vulnerable elements that can be degraded even in fully condensed chromatin, which may correspond to chromatin regions that transfer functionality to the zygote at fertilization. This chapter covers an updated review of our model for sperm chromatin structure and its potential functional elements that affect embryo development.

Effects of oxygen tension and humidity on the preimplantation development of mouse embryos produced by <i>in vitro</i> fertilization: analysis using a non-humidifying incubator with time-lapse cinematography

To examine the effects of oxygen tension and humidity on early embryonic development, the preimplantation development of mouse embryos produced by in vitro fertilization was assessed by time-lapse cinematography to evaluate morphokinetic development with higher precision. Zygotes were produced from spermatozoa and oocytes from ICR mice and cultured in KSOM under low or high oxygen tension in a non-humidified incubator with time-lapse cinematography (CCM-iBIS). The developmental rates of embryos to the 4-cell and blastocyst stages under lower oxygen tension in CCM-iBIS were significantly higher than those under higher oxygen tension in CCM-iBIS. Ninety-six hours after insemination, a large number of embryos cultured under low oxygen tension developed to the hatching blastocyst stage. Embryonic development was more synchronized under lower oxygen tension. Non-humidified cultures did not affect embryonic development. On average, mouse embryos cultured at lower oxygen tension reached 2-cell at 18 h, 3-cell at 39 h, 4-cell at 40 h, initiation of compaction at 58 h, morula at 69 h, and blastocyst at 82 h after insemination. In conclusion, lower oxygen tension better supports preimplantation development of mouse embryos fertilized in vitro, and non-humidified culture conditions do not influence the embryonic development in vitro.

Species-Specific Differences in Sperm Chromatin Decondensation Between Eutherian Mammals Underlie Distinct Lysis Requirements

Sperm present a highly particular DNA condensation that is acquired during their differentiation. Protamines are key elements for DNA condensation. However, whereas the presence of protamine 1 (P1) is conserved across mammalian species, that of protamine 2 (P2) has evolved differentially, existing only few species that use both protamines for sperm DNA condensation. In addition, altered P1/P2 ratios and alterations in the expression of P1 have previously been associated to infertility and DNA damage disorders. On the other hand, different methods evaluating DNA integrity, such as Sperm Chromatin Dispersion (SCD) and Comet tests, need a previous complete DNA decondensation to properly assess DNA breaks. Related with this, the present study aims to analyze the resilience of sperm DNA to decodensation in different eutherian mammals. Sperm samples from humans, horses, cattle, pigs and donkeys were used. Samples were embedded in low melting point agarose and treated with lysis solutions to induce DNA decondensation and formation of sperm haloes. The treatment consisted of three steps: (1) incubation in SDS + DTT for 30 min; (2) incubation in DTT + NaCl for 30 min; and (3) incubation in DTT + NaCl with or without proteinase K for a variable time of 0, 30, or 180 min. How incubation with the third lysis solution (with or without proteinase K) for 0, 30, and 180 min affected DNA decondensation was tested through analyzing core and halo diameters in 50 sperm per sample. Halo/core length ratio was used as an indicator of complete chromatin decondensation. While incubation time with the third lysis solution had no impact on halo/core length ratios in species having P1 and P2 (human, equine and donkey), DNA decondensation of pig and cattle sperm, which only present P1, significantly (P < 0.05) increased following incubation with the third lysis solution for 180 min. In addition, the inclusion of proteinase K was found to accelerate DNA decondensation. In conclusion, longer incubations in lysis solution including proteinase K lead to higher DNA decondensation in porcine and bovine sperm. This suggests that tests intended to analyze DNA damage, such as halo or Comet assays, require complete chromatin deprotamination to achieve high sensitivity in the detection of DNA breaks.

Morphokinetic analysis of pronuclei using time-lapse cinematography in bovine zygotes

The morphokinetics of pronuclei (PN) are considered crucial factors affecting embryogenesis in mammals. Whereas, since bovine zygotes contain a large number of cytosolic lipid droplets, detailed observation of PN has not been performed. In this study, we visualized PN using time-lapse cinematography (TLC) with light microscopy for the first time in delipidated bovine zygotes. The proportions of 0 PN, 1PN, 2PN, and multi-PN in delipidated bovine zygotes were 10.1%, 6.5%, 72.7%, and 10.8%, respectively. Abnormal fertilization, including 1 PN and multi-PN, was observed in 15.6% of blastocysts. The times from IVF to PN appearance, PN fading, and first cleavage in 2 PN bovine zygotes that developed into blastocysts were 10.4, 25.5, and 27.6 h, respectively, which were similar to PN morphokinetics in humans. The 2 PN zygotes showed that the prolonged time from IVF to the appearance of PN and from the fading of PN to the first cleavage negatively affected blastocyst formation. The time from appearance to fading of PN in multi-PN zygotes that developed into blastocysts was longer than that in multi-PN zygotes that did not develop into blastocysts. Besides, among zygotes that developed into blastocysts, the time from appearance to fading of PN in multi-PN zygotes was longer than that in 2 PN and 1 PN zygotes. These results suggest that PN morphokinetic abnormalities are associated with subsequent embryonic development. Observation of PN in bovine zygotes by using non-invasive visible light TLC by delipidation could be a powerful tool to clarify the relationship between PN morphokinetics and developmental competence.

Male advantage observed for in vitro fertilization mouse embryos exhibiting early cleavage

PURPOSE

Mouse embryos forming blastocoele early vs those forming late are predominantly male. We examined whether the male advantage could be recognized at an earlier stage of development.

METHODS

The IVF embryos were classified into early, intermediate, and late development groups based on the time of the third cleavage, and the Zfy and Xist genes were detected to identify their sex in the classified embryos. Furthermore, embryos that were classified based on the time of the third cleavage were transferred to recipient animals and the sex ratio of the fetuses was determined at birth.

RESULTS

Approximately 90% of the early-developing embryos that exhibited third cleavage as early as 47 hours after insemination were male when analyzed using PCR at the blastocyst stage. PCR analysis showed that 61% of the intermediate-developing embryos (third cleavage occurring 48-50 hours after insemination) and 45% of late-developing embryos (third cleavage occurring at 51 hours or later postinsemination) were male. After embryo transfer, the early-developing embryos produced 80% males, while intermediate- and late-developing embryos produced 56% and 45% males, respectively.

CONCLUSIONS

Male embryos tend to develop faster than female embryos during early stage of preimplantation in mice.

The hamster egg penetration test may decrease intracytoplasmic sperm injection utilization while maintaining high conventional fertilization rates

This was a cohort study of in vitro fertilization (IVF) subjects at the University of Utah, Salt Lake City (UT, USA) utilizing partner sperm. Cycles where both the hamster egg penetration test (HEPT) and semen analysis were performed within 2 years prior to IVF cycles were stratified into four groups based on a normal or an abnormal HEPT and morphology. The mean conventional and intracytoplasmic sperm injection (ICSI) fertilization rates were calculated in each group. We performed a univariate analysis on the primary outcome comparing clinically interesting subjects. We performed a cost-effectiveness analysis of a policy of HEPT versus universal ICSI in couples with an abnormal morphology. Among patients with a normal HEPT, there was no difference in the mean conventional fertilization rates between those with a normal and an abnormal morphology. There was no difference in the mean conventional fertilization rates between subjects with a normal morphology without a hamster test and those with a normal HEPT without a morphology assessment. In 1000 simulated cycles with an abnormal morphology, a policy of HEPT was cost saving compared to universal ICSI, yet produced similar fertilization rates. The HEPT is similar to the World Health Organization edition 5 (WHO-5) morphology in predicting successful conventional fertilization while allowing decreased utilization of ICSI. A policy of HEPT for males with abnormal morphology saves cost in selecting couples for a fertilization method.

The epigenetic alterations of human sperm cells caused by heroin use disorder

The molecular mechanisms of drug use on sexual health are largely unknown. We investigated, the relationship between heroin use disorder and epigenetic factors influencing histone acetylation in sperm cells. The volunteers included twenty-four 20- to 50-year-old men with a normal spermogram who did not consume any drugs and twenty-four age- to BMI-matched men who consume only the drug heroin for more than last four months. HDAC1 and HDAC11 mRNA expression levels in spermatozoa and miR-34c-5p and miR-125b-5p expression levels in seminal plasma were measured. The heroin-user group showed significantly increased white blood cell counts and decreased sperm motility and survival rates (8.61 ± 1.73, 21.50 ± 3.11, 69.90 ± 4.69 respectively) as compared to the control group (1.49 ± 0.32, 38.82 ± 3.05, 87.50 ± 0.99 respectively) (p ≤ .001). An increase in DNA fragmentation index (DFI) (heroin-user group: 41.93 ± 6.59% and control group: 10.14 ± 1.43%, p = .003), a change in frequency of HDAC1 (heroin-user group: 1.69 ± 0.55 and control group: 0.45 ± 0.14, p = .045) and HDAC11 (heroin-user group: 0.29 ± 0.13 and control group: 2.36 ± 0.76, p = .019) in spermatozoa and a significant decrease in seminal miR-125b-5p abundance (heroin-user group: 0.37 ± 0.11 and control group: 1.59 ± 0.47, p = .028) were reported in heroin consumers. Heroin use can lead to male infertility by causing leukocytospermia, asthenozoospermia, DFI elevation in sperm cells and alterations in seminal RNA profile.

The Functionally Unannotated Proteome of Human Male Tissues: A Shared Resource to Uncover New Protein Functions Associated with Reproductive Biology

In the context of the Human Proteome Project, we built an inventory of 412 functionally unannotated human proteins for which experimental evidence at the protein level exists (uPE1) and which are highly expressed in tissues involved in human male reproduction. We implemented a strategy combining literature mining, bioinformatics tools to collate annotation and experimental information from specific molecular public resources, and efficient visualization tools to put these unknown proteins into their biological context (protein complexes, tissue and subcellular location, expression pattern). The gathered knowledge allowed pinpointing five uPE1 for which a function has recently been proposed and which should be updated in protein knowledge bases. Furthermore, this bioinformatics strategy allowed to build new functional hypotheses for five other uPE1s in link with phenotypic traits that are specific to male reproductive function such as ciliogenesis/flagellum formation in germ cells (CCDC112 and TEX9), chromatin remodeling (C3orf62) and spermatozoon maturation (CCDC183). We also discussed the enigmatic case of MAGEB proteins, a poorly documented cancer/testis antigen subtype. Tools used and computational outputs produced during this study are freely accessible via ProteoRE (http://www.proteore.org), a Galaxy-based instance, for reuse purposes. We propose these five uPE1s should be investigated in priority by expert laboratories and hope that this inventory and shared resources will stimulate the interest of the community of reproductive biology.

Pregnancy environment, and not preconception, leads to fetal growth restriction and congenital abnormalities associated with diabetes

Maternal diabetes can lead to pregnancy complications and impaired fetal development. The goal of this study was to use a mouse model of reciprocal embryo transfer to distinguish between the preconception and gestational effects of diabetes. To induce diabetes female mice were injected with a single high dose of streptozotocin and 3 weeks thereafter used as oocyte donors for in vitro fertilization (IVF) and as recipients for embryo transfer. Following IVF embryos were cultured to the blastocyst stage in vitro or transferred to diabetic and non-diabetic recipients. Diabetic and non-diabetic females did not differ in regard to the number of oocytes obtained after ovarian stimulation, oocytes ability to become fertilized, and embryo development in vitro. However, diabetic females displayed impaired responsiveness to superovulation. Reciprocal embryo transfer resulted in similar incidence of live fetuses and abortions, and no changes in placental size. However, fetuses carried by diabetic recipients were smaller compared to those carried by non-diabetic recipients, regardless hyperglycemia status of oocyte donors. Congenital abnormalities were observed only among the fetuses carried by diabetic recipients. The findings support that the diabetic status during pregnancy, and not the preconception effect of diabetes on oogenesis, leads to fetal growth restriction and congenital deformities.

Etiologies of sperm DNA damage and its impact on male infertility

Male factor is responsible for up to 50% of infertility cases in the world. Semen analysis is considered the cornerstone of laboratory evaluation of male infertility, but it has its own drawbacks and fails to predict the male fertility potential with high sensitivity and specificity. Different etiologies have been linked with male infertility, of which sperm DNA damage has gained significant attention with extensive research on sperm function tests. The associations between sperm DNA damage and a variety of disorders such as varicocele, obesity, cancer, radiation and lifestyle factors are explored in this review. Furthermore, we discuss the mechanisms of DNA damage as well as its impact in different scenarios of male infertility, associated with spontaneous and assisted reproduction. Finally, we review the clinical applicability of sperm DNA fragmentation testing in the management of male infertility.

Comparison of ART outcomes in men with altered mRNA protamine 1/protamine 2 ratio undergoing intracytoplasmic sperm injection with ejaculated and testicular spermatozoa

Assisted reproductive technologies involving the use of spermatozoa and eggs for in vitro fertilization (IVF) have come as the solution for many infertile couples to become parents. However, in some cases, the use of ejaculated spermatozoa delivers poor IVF performance. Some studies have suggested the use of testicular spermatozoa in severe male infertility cases, but no guidelines regarding their utilization are currently available. In the present study, we found the mRNA protamine 1/protamine 2 (P1/P2) ratio to be a valuable biomarker of poor sperm function that could be used as a diagnostic key for the identification of cases that would benefit from the use of testicular spermatozoa. A total of 23 couples undergoing egg donation cycles with at least one previous cycle failure were studied. All couples underwent two consecutive intracytoplasmic sperm injection (ICSI) cycles with either ejaculated or testicular spermatozoa (TESA). The sperm mRNA P1/P2 ratio, fertilization rate, blastocyst rate, and pregnancy and live birth rate were compared. Results showed improved ICSI and clinical outcomes in cycles with testicular spermatozoa in men with altered mRNA P1/P2 ratios. TESA cycles presented significantly higher rates of fertilization (mean ± standard deviation: 76.1% ± 15.1% vs 65.5% ± 18.8%), blastocyst formation (55.0% ± 20.3% vs 30.8% ± 23.8%), and good morphological quality blastocyst (28.9% ± 22.9% vs 13.5% ± 17.9%) and also improvements on pregnancy (60.9% vs 0%) and healthy birth rates (56.5% vs 0%) than EJACULATE cycles. The results described here suggest that in patients with previous IVF/ICSI failures and aberrant mRNA protamine ratios, the use of testicular spermatozoa may be a good alternative to improve clinical outcomes.

In the human sperm nucleus, nucleosomes form spatially restricted domains consistent with programmed nucleosome positioning

In human sperm, a fraction of its chromatin retains nucleosomes that are positioned on specific sequences containing genes and regulatory units essential for embryonic development. This nucleosome positioning (NP) feature provides an inherited epigenetic mark for sperm. However, it is not known whether there is a structural constraint for these nucleosomes and, if so, how they are localized in a three-dimensional (3D) context of the sperm nucleus. In this study, we examine the 3D organization of sperm chromatin and specifically determine its 3D localization of nucleosomes using structured illumination microscopy. A fraction of the sperm chromatin form nucleosome domains (NDs), visible as microscopic puncta ranging from 40 μm to 700 μm in diameter, and these NDs are precisely localized in the post acrosome region (PAR), outside the sperm's core chromatin. Further, NDs exist mainly in sperm from fertile men in a pilot survey with a small sample size. Together, this study uncovers a new spatially-restricted sub-nuclear structure containing NDs that are consistent with NPs of the sperm, which might represent a novel mark for healthy sperm in human.

Rescue of Sly Expression Is Not Sufficient to Rescue Spermiogenic Phenotype of Mice with Deletions of Y Chromosome Long Arm

Mice with deletions of the Y-specific (non-PAR) region of the mouse Y chromosome long arm (NPYq) have sperm defects and fertility problems that increase proportionally to deletion size. Mice with abrogated function of NPYq-encoded gene Sly (sh367 Sly-KD) display a phenotype similar to that of NPYq deletion mutants but less severe. The milder phenotype can be due to insufficient Sly knockdown, involvement of another NPYq gene, or both. To address this question and to further elucidate the role of Sly in the infertile phenotype of mice with NPYq deletions, we developed an anti-SLY antibody specifically recognizing SLY1 and SLY2 protein isoforms and used it to characterize SLY expression in NPYq- and Sly-deficient mice. We also carried out transgene rescue by adding Sly1/2 transgenes to mice with NPYq deletions. We demonstrated that SLY1/2 expression in mutant mice decreased proportionally to deletion size, with ~12% of SLY1/2 retained in shSLY sh367 testes. The addition of Sly1/2 transgenes to mice with NPYq deletions rescued SLY1/2 expression but did not ameliorate fertility and testicular/spermiogenic defects. Together, the data suggest that Sly deficiency is not the sole underlying cause of the infertile phenotype of mice with NPYq deletions and imply the involvement of another NPYq gene.

Risk of chromosomal aberration in spermatozoa during intracytoplasmic sperm injection

Intracytoplasmic sperm injection (ICSI) has become critical for the treatment of severe male infertility. The principal feature of ICSI is the direct injection of spermatozoon into an oocyte, which facilitates the production of fertilized embryos regardless of semen characteristics, such as sperm concentration and motility. However, the chromosomal integrity of ICSI zygotes is degraded compared to that of zygotes obtained via in vitro fertilization. This chromosomal damage may occur due to the injection of non-capacitated, acrosome-intact spermatozoa, which never enter the oocytes under natural fertilization. Furthermore, it is possible that the in vitro incubation and pre-treatment of spermatozoa during ICSI results in DNA damage. Chromosomal aberrations in embryos induce early pregnancy losses. However, these issues may be overcome by embryo production using gametes with guaranteed chromosomal integrity. Because conventional chromosome analysis requires fixing cells to obtain the chromosome spreads, embryos cannot be produced using the nucleus that has been analyzed. On the other hand, genome cloning using androgenic or gynogenic embryos provides an additional nucleus for chromosome analysis following embryo production. Thus, this review aims to highlight the hazardous nature of chromosomal aberrations in sperm during ICSI and to introduce a method for the prezygotic examination for chromosomal aberrations.

Production of inbred offspring by intracytoplasmic sperm injection of oocytes from juvenile female mice

The aim of the present study was to determine whether the use of oocytes from juvenile female mice would improve the efficiency of intracytoplasmic sperm injection (ICSI). In the present study, 15 adult and 14 juvenile C57BL6/J female mice were superovulated, with 17.8 oocytes per mouse harvested from adults, significantly lower than the 40.2 harvested from juveniles (P<0.01). Sixty and 233 oocytes were harvested from C57BL/6J adult and juvenile mice respectively, activated in 10mM SrCl2+5μgmL-1 cytochalasin B for 5-6h and cultured in potassium simplex optimisation medium (KSOM) for 3.5 days, with no differences in morula and blastocyst rates between groups (91.7% vs 96.6%; P>0.05). Twelve hours after injection of human chorionic gonadotrophin, oocytes were harvested from C57BL/6J juvenile mice into KSOM, randomly divided into groups and activated with the same method mentioned above at 0, 2, 4 or 6h and then cultured in KSOM for 3.5 days. There was no significant difference in morula and blastocyst rates among the different groups (P>0.05). Oocytes from juvenile mice activated in 10mM SrCl2 for 2h were subjected to ICSI and the rates of pronuclear formation and Day 1 cleavage were significantly improved compared with the control group (P<0.01). ICSI combined with activation of oocytes from inbred mouse strains (C57BL/6J, C57BL/6N and 129Svev) successfully produced pups. The fertility of some these mice resulting from ICSI was tested, and the animals proved fertile. In conclusion, superovulated juvenile mice can yield more useable oocytes than adult mice, but additional activation is essential for full development of ICSI oocytes harvested from juvenile inbred mice.

Defective sperm head decondensation undermines the success of ICSI in the bovine

The efficiency of intracytoplasmic sperm injection (ICSI) in the bovine is low compared to other species. It is unknown whether defective oocyte activation and/or sperm head decondensation limit the success of this technique in this species. To elucidate where the main obstacle lies, we used homologous and heterologous ICSI and parthenogenetic activation procedures. We also evaluated whether in vitro maturation negatively impacted the early stages of activation after ICSI. Here we showed that injected bovine sperm are resistant to nuclear decondensation by bovine oocytes and this is only partly overcome by exogenous activation. Remarkably, when we used heterologous ICSI, in vivo-matured mouse eggs were capable of mounting calcium oscillations and displaying normal PN formation following injection of bovine sperm, although in vitro-matured mouse oocytes were unable to do so. Together, our data demonstrate that bovine sperm are especially resistant to nuclear decondensation by in vitro-matured oocytes and this deficiency cannot be simply overcome by exogenous activation protocols, even by inducing physiological calcium oscillations. Therefore, the inability of a suboptimal ooplasmic environment to induce sperm head decondensation limits the success of ICSI in the bovine. Studies aimed to improve the cytoplasmic milieu of in vitro-matured oocytes and to replicate the molecular changes associated with in vivo capacitation and acrosome reaction will deepen our understanding of the mechanism of fertilization and improve the success of ICSI in this species.

SIRT1-dependent modulation of methylation and acetylation of histone H3 on lysine 9 (H3K9) in the zygotic pronuclei improves porcine embryo development

Background

The histone code is an established epigenetic regulator of early embryonic development in mammals. The lysine residue K9 of histone H3 (H3K9) is a prime target of SIRT1, a member of NAD⁺-dependent histone deacetylase family of enzymes targeting both histone and non-histone substrates. At present, little is known about SIRT1-modulation of H3K9 in zygotic pronuclei and its association with the success of preimplantation embryo development. Therefore, we evaluated the effect of SIRT1 activity on H3K9 methylation and acetylation in porcine zygotes and the significance of H3K9 modifications for early embryonic development.

Results

Our results show that SIRT1 activators resveratrol and BML-278 increased H3K9 methylation and suppressed H3K9 acetylation in both the paternal and maternal pronucleus. Inversely, SIRT1 inhibitors nicotinamide and sirtinol suppressed methylation and increased acetylation of pronuclear H3K9. Evaluation of early embryonic development confirmed positive effect of selective SIRT1 activation on blastocyst formation rate (5.2 ± 2.9% versus 32.9 ± 8.1% in vehicle control and BML-278 group, respectively; P ≤ 0.05). Stimulation of SIRT1 activity coincided with fluorometric signal intensity of ooplasmic ubiquitin ligase MDM2, a known substrate of SIRT1 and known limiting factor of epigenome remodeling.

Conclusions

We conclude that SIRT1 modulates zygotic histone code, obviously through direct deacetylation and via non-histone targets resulting in increased H3K9me3. These changes in zygotes lead to more successful pre-implantation embryonic development and, indeed, the specific SIRT1 activation due to BML-278 is beneficial for in vitro embryo production and blastocyst achievement.

Sperm capacitation pretreatment positively impacts bovine intracytoplasmic sperm injection

The efficiency of intracytoplasmic sperm injection (ICSI) in bovines is low compared to other species due in part to inadequate egg activation and sperm nucleus decondensation after injection. We hypothesized that this low efficiency is due to the lack of complete sperm capacitation, so we evaluated the effects of isobutylmethylxanthine (IBMX) and methyl-β-cyclodextrin (MβCD) on bovine sperm capacitation and on the preimplantation developmental potential of bovine embryos generated by ICSI. Treatment with IBMX and MβCD decreased sperm viability (between 13-30%); nevertheless, 0.4 mM IBMX and 1 mM MβCD increased (p < 0.05) capacitation metrics-that is, acrosome exocytosis, intracellular calcium level, plasma membrane fluidity, and tyrosine phosphorylation-compared to the control. After ICSI, embryos injected with IBMX- and MβCD-treated sperm showed similar cleavage to the untreated group (range 82-88%). Pronucleus formation rate was higher with MβCD-pretreatment (54%) compared to the control group (25%), and blastocyst rate was significantly improved with MβCD-pretreatment (24%) compared to the IBMX (18%) and control (17%) groups. Importantly, embryo quality-as assessed by the total number of cells, cell allocation, and apoptotic cell index-was not affected by the sperm treatments. In conclusion, MβCD pretreatment of sperm improved the efficiency of blastocyst production in bovine ICSI.

Effect of sperm pretreatment with glutathione and membrane destabilizing agents lysolecithin and Triton X-100, on the efficiency of bovine intracytoplasmic sperm injection

Intracytoplasmic sperm injection (ICSI) is an assisted reproduction tool with several applications. Its effectiveness in bovines is lower than that in other species, mainly because of difficulties in the decondensation of the sperm nucleus after injection, and the presence of the acrosome and the plasma membrane which remain intact in this procedure. In this study, we assessed the effect of lysolecithin (LL) and Triton X-100 (TX), in combination with glutathione (GSH) as sperm pretreatments prior to ICSI. The GSH-LL and GSH-TX groups showed 0% of spermatozoa with intact membrane (SYBR 14+/PI), in comparison with the control (63.3%) and GSH (65.7%) groups. The proportions of spermatozoa with damaged acrosome membrane in the GSH-LL, GSH-TX, GSH and control groups were 46%, 35.9%, 10.5% and 7.5%, respectively. Sperm chromatin decondensation analysis showed that the groups incubated for 3 hr with GSH presented greater decondensation (p < .05). Although fertilization was improved in all treatment groups evaluated, no differences were observed in the cleavage rate 72 hr after activation in the GSH (73.7%), GSH-LL (80.2%) and GSH-TX (77.8%) groups compared to the control (66.3%), neither in the blastocyst rate on day 8 (24.0%, 26.2%, 27.1% and 28.4% for the control, GSH, GSH-LL and GSH-TX groups, respectively). No differences were also observed in the total number of cells in all groups. In conclusion, although these sperm treatments promoted nuclear decondensation and induced plasma membrane disruption, these effects were not sufficient to improve bovine embryonic development after ICSI.

Oocyte Activation and Fertilisation: Crucial Contributors from the Sperm and Oocyte

This chapter intends to summarise the importance of sperm- and oocyte-derived factors in the processes of sperm-oocyte binding and oocyte activation. First, we describe the initial interaction between sperm and the zona pellucida, with particular regard to acrosome exocytosis. We then describe how sperm and oocyte membranes fuse, with special reference to the discovery of the sperm protein IZUMO1 and its interaction with the oocyte membrane receptor JUNO. We then focus specifically upon oocyte activation, the fundamental process by which the oocyte is alleviated from metaphase II arrest by a sperm-soluble factor. The identity of this sperm factor has been the source of much debate recently, although mounting evidence, from several different laboratories, provides strong support for phospholipase C ζ (PLCζ), a sperm-specific phospholipase. Herein, we discuss the evidence in support of PLCζ and evaluate the potential role of other candidate proteins, such as post-acrosomal WW-binding domain protein (PAWP/WBP2NL). Since the cascade of downstream events triggered by the sperm-borne oocyte activation factor heavily relies upon specialised cellular machinery within the oocyte, we also discuss the critical role of oocyte-borne factors, such as the inositol trisphosphate receptor (IP₃R), protein kinase C (PKC), store-operated calcium entry (SOCE) and calcium/calmodulin-dependent protein kinase II (CaMKII), during the process of oocyte activation. In order to place the implications of these various factors and processes into a clinical context, we proceed to describe their potential association with oocyte activation failure and discuss how clinical techniques such as the in vitro maturation of oocytes may affect oocyte activation ability. Finally, we contemplate the role of artificial oocyte activating agents in the clinical rescue of oocyte activation deficiency and discuss options for more endogenous alternatives.

Mammalian sperm nuclear organization: resiliencies and vulnerabilities

Sperm cells are remarkably complex and highly specialized compared to somatic cells. Their function is to deliver to the oocyte the paternal genomic blueprint along with a pool of proteins and RNAs so a new generation can begin. Reproductive success, including optimal embryonic development and healthy offspring, greatly depends on the integrity of the sperm chromatin structure. It is now well documented that DNA damage in sperm is linked to reproductive failures both in natural and assisted conception (Assisted Reproductive Technologies [ART]). This manuscript reviews recent important findings concerning - the unusual organization of mammalian sperm chromatin and its impact on reproductive success when modified. This review is focused on sperm chromatin damage and their impact on embryonic development and transgenerational inheritance.

Mouse Y-Encoded Transcription Factor Zfy2 Is Essential for Sperm Formation and Function in Assisted Fertilization

Spermatogenesis is a key developmental process allowing for a formation of a mature male gamete. During its final phase, spermiogenesis, haploid round spermatids undergo cellular differentiation into spermatozoa, which involves extensive restructuring of cell morphology, DNA, and epigenome. Using mouse models with abrogated Y chromosome gene complements and Y-derived transgene we identified Y chromosome encoded Zfy2 as the gene responsible for sperm formation and function. In the presence of a Zfy2 transgene, mice lacking the Y chromosome and transgenic for two other Y-derived genes, Sry driving sex determination and Eif2s3y initiating spermatogenesis, are capable of producing sperm which when injected into the oocytes yield live offspring. Therefore, only three Y chromosome genes, Sry, Eif2s3y and Zfy2, constitute the minimum Y chromosome complement compatible with successful intracytoplasmic sperm injection in the mouse.

The mammalian Y chromosome was once thought to be a genetic wasteland with testis determinant Sry being the only gene of importance. We now know that there are many genes on this chromosome crucial for male reproduction but their specific roles are often undefined. Here, we investigated the function of the Y chromosome gene Zfy2 during a final step of male gamete formation. We demonstrated that Zfy2 is responsible for allowing sperm precursor cells, haploid round spermatids, to undergo transformation into spermatozoa, and that these sperm are capable of yielding live offspring when injected into the oocytes. Thus, we identified a novel role of the Zfy2 gene during spermatogenesis and fertilization. Considering that in human sperm formation is a prerequisite for male infertility treatment using assisted reproduction technologies, our finding bear translational significance.

In vitro fertilization (IVF) in mammals: epigenetic and developmental alterations. Scientific and bioethical implications for IVF in humans

The advent of in vitro fertilization (IVF) in animals and humans implies an extraordinary change in the environment where the beginning of a new organism takes place. In mammals fertilization occurs in the maternal oviduct, where there are unique conditions for guaranteeing the encounter of the gametes and the first stages of development of the embryo and thus its future. During this period a major epigenetic reprogramming takes place that is crucial for the normal fate of the embryo. This epigenetic reprogramming is very vulnerable to changes in environmental conditions such as the ones implied in IVF, including in vitro culture, nutrition, light, temperature, oxygen tension, embryo-maternal signaling, and the general absence of protection against foreign elements that could affect the stability of this process. The objective of this review is to update the impact of the various conditions inherent in the use of IVF on the epigenetic profile and outcomes of mammalian embryos, including superovulation, IVF technique, embryo culture and manipulation and absence of embryo-maternal signaling. It also covers the possible transgenerational inheritance of the epigenetic alterations associated with assisted reproductive technologies (ART), including its phenotypic consequences as is in the case of the large offspring syndrome (LOS). Finally, the important scientific and bioethical implications of the results found in animals are discussed in terms of the ART in humans.

Sry-Independent Overexpression of Sox9 Supports Spermatogenesis and Fertility in the Mouse

The Y chromosome gene Sry is responsible for sex determination in mammals and initiates a cascade of events that direct differentiation of bipotential genital ridges toward male-specific fate. Sox9 is an autosomal gene and a primary downstream target of SRY. The activation of Sox9 in the absence of Sry is sufficient for initiation of male-specific sex determination. Sry-to-Sox9 replacement has mostly been studied in the context of sex determination during early embryogenesis. Here, we tested whether Sry-to-Sox9 replacement affects male fertility in adulthood. We examined males with the Y chromosome carrying a deletion removing the endogenous Sry, with testes determination driven either by the Sox9 (XY(Tdym1)Sox9) or the Sry (XY(Tdym1)Sry) transgenes as well as wild-type males (XY). XY(Tdym1)Sox9 males had reduced testes size, altered testes shape and vasculature, and increased incidence of defects in seminiferous epithelium underlying the coelomic blood vessel region when compared to XY(Tdym1)Sry and XY. There were no differences between XY(Tdym1)Sry and XY(Tdym1)Sox9 males in respect to sperm number, motility, morphology, and ability to fertilize oocytes in vitro, but for some parameters, transgenic males were impaired when compared to XY. In fecundity trials, XY(Tdym1)Sry, XY(Tdym1)Sox9, and XY males yielded similar average numbers of pups and litters. Overall, our findings support that males lacking the testis determinant Sry can be fertile and reinforce the notion that Sry does not play a role in mature gonads. Although transgenic Sox9 overexpression in the absence of Sry results in certain testicular abnormalities, it does not translate into fertility impairment.

Changes in Sperm Motility and Capacitation Induce Chromosomal Aberration of the Bovine Embryo following Intracytoplasmic Sperm Injection

Intracytoplasmic sperm injection (ICSI) has become the method of choice to treat human male infertility. One of the outstanding problems associated with this technique is our current lack of knowledge concerning the effect of sperm capacitation and motility upon the subsequent development of oocytes following ICSI. In the present study, we first examined the capacitation state of sperm exhibiting normal motility, along with sperm that had been activated, and examined the effect of reactive oxygen species (ROS) produced by these sperm types upon embryogenesis following bovine in vitro fertilization (IVF) and ICSI. Data showed that activated sperm reduced the chromosomal integrity of IVF/ICSI embryos at the blastocyst stage, while capacitated sperm produced ROS in capacitation media. Secondly, we treated sperm with carbonyl cyanide m-chlorophenyl hydrazine (CCCP), a chemical known to uncouple cell respiration within the mitochondria, and investigated the effect of this treatment upon blastocyst formation and chromosomal integrity at the blastocyst stage. Activated sperm in which the mitochondria had been treated with CCCP reduced levels of chromosomal aberration at the blastocyst stage following ICSI, by reducing mitochondrial activity in activated sperm. In conclusion, these findings suggest that capacitated sperm exhibiting activated motility induced chromosomal aberration during development to the blastocyst stage following ICSI. The injection of sperm exhibiting normal motility, or activated sperm in which mitochondrial activity had been reduced, improved the quality of ICSI-derived embryos. Therefore, the selection of sperm exhibiting progressive motility may not always be better for early embryo development and fetal growth following human ICSI, and that the use of a bovine model may contribute to a deeper understanding of sperm selection for human ICSI embryo development.

Potential Health Risks Associated to ICSI: Insights from Animal Models and Strategies for a Safe Procedure

Artificial reproductive techniques are currently responsible for 1.7–4% of the births in developed countries and intracytoplasmatic sperm injection (ICSI) is the most commonly used, accounting for 70–80% of the cycles performed. Despite being an invaluable tool for infertile couples, the technique bypasses several biological barriers that naturally select the gametes to achieve an optimal embryonic and fetal development. In this perspective, ICSI has been associated with an increased risk for diverse health problems, ranging from premature births and diverse metabolic disorders in the offspring to more severe complications such as abortions, congenital malformations, and imprinting disorders. In this review, we discuss the possible implications of the technique per se on these adverse outcomes and highlight the importance of several experiments using mammalian models to truthfully test these implications and to uncover the molecular base that origins these health problems. We also dissect the specific hazards associated to ICSI and describe some strategies that have been developed to mimic the gamete selection occurring in natural conception in order to improve the safety of the procedure.

Recent knowledge concerning mammalian sperm chromatin organization and its potential weaknesses when facing oxidative challenge

Spermatozoa are the smallest and most cyto-differentiated mammalian cells. From a somatic cell-like appearance at the beginning of spermatogenesis, the male germ cell goes through a highly sophisticated process to reach its final organization entirely devoted to its mission which is to deliver the paternal genome to the oocyte. In order to fit the paternal DNA into the tiny spermatozoa head, complete chromatin remodeling is necessary. This review essentially focuses on present knowledge of this mammalian sperm nucleus compaction program. Particular attention is given to most recent advances that concern the specific organization of mammalian sperm chromatin and its potential weaknesses. Emphasis is placed on sperm DNA oxidative damage that may have dramatic consequences including infertility, abnormal embryonic development and the risk of transmission to descendants of an altered paternal genome.

Germline transgenesis in rodents by pronuclear microinjection of Sleeping Beauty transposons

We describe a protocol for high-efficiency germline transgenesis and sustained transgene expression in two important biomedical models, the mouse and the rat, by using the Sleeping Beauty transposon system. The procedure is based on co-injection of synthetic mRNA encoding the SB100X hyperactive transposase, together with circular plasmid DNA carrying a transgene construct flanked by binding sites for the transposase, into the pronuclei of fertilized oocytes. Upon translation of the transposase mRNA, enzyme-mediated excision of the transgene cassettes from the injected plasmids followed by permanent genomic insertion produces stable transgenic animals. Generation of a germline-transgenic founder animal by using this protocol takes ∼3 months. Transposon-mediated transgenesis compares favorably in terms of both efficiency and reliable transgene expression with classic pronuclear microinjection, and it offers comparable efficacies to lentiviral approaches without limitations on vector design, issues of transgene silencing, and the toxicity and biosafety concerns of working with viral vectors.

Understanding the spermatozoon

The former perception of the spermatozoon as a delivery device of the male genome has been expanded to include a new understanding of the cell's complex role in fertilization. Once the spermatozoon reaches the oocyte, it triggers egg activation and orchestrates the stages of pre- and post-fertilization in a preprogrammed pattern while tapping the oocyte's resources in an effort to generate a new life.

Effects of embryonic manipulation and epigenetics

Embryonic manipulation techniques, such as in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), are widely used in assisted reproductive technology (ART), livestock propagation and application in other fields. Fertilization with IVF and ICSI have been shown to be highly effective, and the mice produced by these techniques develop healthily and with a normal appearance. However, there remains a possibility of epigenetic changes being induced by these techniques. The early stage of mammalian development from fertilization to implantation is a period in which global changes in the epigenetic landscape take place. The sperm and oocyte epigenetic profiles are very different from each other, and the epigenetic remodeling process after fertilization exhibits allelic differences. It is during this period that embryonic manipulation is performed. In this review, I discuss the effects of embryonic manipulation procedures in relation to the epigenetic asymmetry that is present in mammalian early development. Such regulation in the preimplantation embryo provides an important insight into epigenetics.

Embryo manipulation via assisted reproductive technology and epigenetic asymmetry in mammalian early development

The early stage of mammalian development from fertilization to implantation is a period when global and differential changes in the epigenetic landscape occur in paternally and maternally derived genomes, respectively. The sperm and egg DNA methylation profiles are very different from each other, and just after fertilization, only the paternally derived genome is subjected to genome-wide hydroxylation of 5-methylcytosine, resulting in an epigenetic asymmetry in parentally derived genomes. Although most of these differences are not present by the blastocyst stage, presumably due to passive demethylation, the maintenance of genomic imprinting memory and X chromosome inactivation in this stage are of critical importance for post-implantation development. Zygotic gene activation from paternally or maternally derived genomes also starts around the two-cell stage, presumably in a different manner in each of them. It is during this period that embryo manipulation, including assisted reproductive technology, is normally performed; so it is critically important to determine whether embryo manipulation procedures increase developmental risks by disturbing subsequent gene expression during the embryonic and/or neonatal development stages. In this review, we discuss the effects of various embryo manipulation procedures applied at the fertilization stage in relation to the epigenetic asymmetry in pre-implantation development. In particular, we focus on the effects of intracytoplasmic sperm injection that can result in long-lasting transcriptome disturbances, at least in mice.

Mouse zygotes respond to severe sperm DNA damage by delaying paternal DNA replication and embryonic development

Mouse zygotes do not activate apoptosis in response to DNA damage. We previously reported a unique form of inducible sperm DNA damage termed sperm chromatin fragmentation (SCF). SCF mirrors some aspects of somatic cell apoptosis in that the DNA degradation is mediated by reversible double strand breaks caused by topoisomerase 2B (TOP2B) followed by irreversible DNA degradation by a nuclease(s). Here, we created zygotes using spermatozoa induced to undergo SCF (SCF zygotes) and tested how they responded to moderate and severe paternal DNA damage during the first cell cycle. We found that the TUNEL assay was not sensitive enough to identify the breaks caused by SCF in zygotes in either case. However, paternal pronuclei in both groups stained positively for γH2AX, a marker for DNA damage, at 5 hrs after fertilization, just before DNA synthesis, while the maternal pronuclei were negative. We also found that both pronuclei in SCF zygotes with moderate DNA damage replicated normally, but paternal pronuclei in the SCF zygotes with severe DNA damage delayed the initiation of DNA replication by up to 12 hrs even though the maternal pronuclei had no discernable delay. Chromosomal analysis of both groups confirmed that the paternal DNA was degraded after S-phase while the maternal pronuclei formed normal chromosomes. The DNA replication delay caused a marked retardation in progression to the 2-cell stage, and a large portion of the embryos arrested at the G2/M border, suggesting that this is an important checkpoint in zygotic development. Those embryos that progressed through the G2/M border died at later stages and none developed to the blastocyst stage. Our data demonstrate that the zygote responds to sperm DNA damage through a non-apoptotic mechanism that acts by slowing paternal DNA replication and ultimately leads to arrest in embryonic development.

Sperm capacitation combined with removal of the sperm acrosome and plasma membrane enhances paternal nucleus remodelling and early development of bovine androgenetic embryos

The androgenetic embryo is a useful model for functional analysis of the paternal genome during embryogenesis. However, few studies have focused on the factors involved in the suppressed developmental competence of such embryos or why sperm cloning-derived androgenetic embryos fail to develop beyond the morula stage in large domestic animals. To overcome this developmental failure, we tried to improve sperm decondensation, as well as to enhance embryonic development by sperm capacitation and removal of the acrosome and plasma membrane before injection of the spermatozoa. Before injection of the spermatozoa, we quantified the effects of sperm capacitation combined with sperm pretreatment on the acrosome and plasma membrane status. We also evaluated sperm decondensation potential, sperm viability and chromatin integrity. Immunostaining data showed that the sperm acrosome and plasma membrane could be more efficiently removed after capacitation. Dithiothreitol-induced sperm decondensation potential was improved with capacitation and removal of the acrosome and plasma membrane. Although most spermatozoa lost viability after pretreatment, their chromatin remained integrated. The patterns of paternal chromatin remodelling within uncleaved androgenetic embryos and the nucleus morphology of cleaved embryos indicated that capacitation combined with membrane disruption could make injected spermatozoa decondense synchronously not only with each other, but also with the developmental pace of the ooplasm. We successfully produced androgenetic blastocysts, and efficiency increased with sperm pretreatment. In conclusion, sperm decondensation and the early development of androgenetic embryos were enhanced with sperm capacitation and removal of the acrosome and plasma membrane prior to sperm injection.

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.

Deficiency of the multi-copy mouse Y gene Sly causes sperm DNA damage and abnormal chromatin packaging

In mouse and man Y chromosome deletions are frequently associated with spermatogenic defects. Mice with extensive deletions of non-pairing Y chromosome long arm (NPYq) are infertile and produce sperm with grossly misshapen heads, abnormal chromatin packaging and DNA damage. The NPYq-encoded multi-copy gene Sly controls the expression of sex chromosome genes after meiosis and Sly deficiency results in a remarkable upregulation of sex chromosome genes. Sly deficiency has been shown to be the underlying cause of the sperm head anomalies and infertility associated with NPYq gene loss, but it was not known whether it recapitulates sperm DNA damage phenotype. We produced and examined mice with transgenically (RNAi) silenced Sly and demonstrated that these mice have increased incidence of sperm with DNA damage and poorly condensed and insufficiently protaminated chromatin. We also investigated the contribution of each of the two Sly-encoded transcript variants and noted that the phenotype was only observed when both variants were knocked down, and that the phenotype was intermediate in severity compared with mice with severe NPYq deficiency. Our data demonstrate that Sly deficiency is responsible for the sperm DNA damage/chromatin packaging defects observed in mice with NPYq deletions and point to SLY proteins involvement in chromatin reprogramming during spermiogenesis, probably through their effect on the post-meiotic expression of spermiogenic genes. Considering the importance of the sperm epigenome for embryonic and fetal development and the possibility of its inter-generational transmission, our results are important for future investigations of the molecular mechanisms of this biologically and clinically important process.

Biopsy of embryos produced by in vitro fertilization affects development in C57BL/6 mouse strain

Preimplantation genetic diagnosis is considered highly successful with respect to its accuracy in detecting genetic anomalies, although the effects of embryo biopsy on embryonic and fetal growth and development are less known, particularly in conjunction with IVF. Here, we compared biopsied (B) and nonbiopsied (NB) mouse embryos for developmental competence. Embryos C57BL/6 (B6) and B6D2F2 (F2) generated by IVF were subjected to single blastomere biopsy at the four-cell stage, and were either cultured for 120 h and subjected to differential inner cell mass (ICM) and trophoblast staining, or were transferred into the uterine tubes of surrogate mothers after 72 h of culture, to examine their pre- and postimplantation development, respectively. NB embryos from the same IVF cohorts served as controls. Embryo biopsy negatively affected preimplantation development to blastocyst in C57BL/6 (69% vs. 79%; P < 0.01), but not in B6D2F1 mice (89% vs. 91%; P = not significant [NS]). Although B6 embryos had lower total cell number than F2 (B6: 47 and 61 vs. F2: 53 and 70; B and NB, respectively; P < 0.05) there were no differences between B and NB blastocysts in percentage of ICM (B6: 19.8 vs. 19.8; F2: 20.9 vs. 20.4; P = NS) and ICM:trophoblast ratio (B6: 4.7 vs. 4.7; F2: 4.4 vs. 4.7) in both mouse strains. Postimplantation development to live fetuses of B embryos as compared with NB counterparts was impaired in C57BL/6 (6% vs. 18%; P < 0.001) but not in B6D2F1 mice (26% vs. 35%; P = NS). We concluded that blastomere biopsy impaired embryonic and fetal development in mice known to be sensitive to in vitro culture and manipulations. Such mice are models for infertile couples with poor quality gametes seeking assisted reproduction technologies.

Sperm pretreatment with dithiothreitol increases male pronucleus formation rates after intracytoplasmic sperm injection (ICSI) in swamp buffalo oocytes

Failure of male pronucleus formation has hampered the success of intracytoplasmic sperm injection (ICSI) in swamp buffalo. The aim of the present study was to improve male pronucleus formation by pretreating sperm with various chemicals before ICSI. In Experiments1 and 2, sperm were treated according to one of the following protocols: (1) 0.1% Triton-X 100 (TX) for 1 min, (2) 10 µM calcium ionophore (CaI) for 20 min, (3) freezing and thawing (FT) without any cryoprotectant, or (4) no treatment (control). These sperm treatment groups then either did or did not receive additional sperm treatment with 5 mM dithiothreitol (DTT) for 20 min. Acrosomal integrity (Experiment 1) and DNA fragmentation (Experiment 2) were evaluated in the sperm before ICSI. In Experiment 3, oocytes matured in vitro were subjected to ICSI using pretreated sperm as described above and then were cultured either with or without activation. The TX- and CaI-treated sperm caused an increase in the number of acrosome-loss sperm, whereas the FT treatment and control increased the proportion of acrosome-reacted sperm (P<0.05). The DNA fragmentation did not differ among treatments (P>0.05). At 18 h post-ICSI, pronucleus (PN) formation was found only in activated oocytes. The majority of the activated ICSI oocytes contained intact sperm heads. Normal fertilization was observed in the CaI and FT treatment groups and control group when sperm were treated with DTT before ICSI. In conclusion, DTT treatment of sperm with reacted acrosomes before ICSI together with activation of the ICSI oocytes is important for successful male pronucleus formation.

Sperm DNA damage: how relevant is it clinically?

PURPOSE OF REVIEW

The true impact of the current sperm DNA fragmentation testing needs further scrutiny to assess whether clinically meaningful information is conveyed.

RECENT FINDINGS

Various studies have suggested different or no threshold values with assorted tests for the percentage of DNA fragmentation in the ejaculated sperm above which natural conception, fertilization or embryo development and/or clinical pregnancy rates are compromised. Current DNA fragmentation assessment methods provide very little specific information on the nature and severity of the DNA damage detected. Although sperm DNA fragmentation is associated with lower pregnancy rates through natural conception or intrauterine insemination, it does not seem to affect intracytoplasmic sperm injection outcome. Although animal studies demonstrated adverse reproductive effects of sperm DNA fragmentation, any conclusive evidence in humans is yet to be demonstrated. It is not clear whether interventions aimed at enrichment of sperm with decreased DNA fragmentation are effective in preventing the potential adverse effects of sperm DNA fragmentation in humans. Major concern about the use of sperm DNA integrity tests as prognostic parameters is that the direct evaluation of DNA fragmentation in individual sperm fertilizing the oocyte is not possible.

SUMMARY

The lack of consensus in defining a clinically relevant standard DNA fragmentation test with a meaningful cut-off level brings challenges in implementing the routine use of sperm DNA integrity assessment in daily practice.

Unique pattern of ORC2 and MCM7 localization during DNA replication licensing in the mouse zygote

In eukaryotes, DNA synthesis is preceded by licensing of replication origins. We examined the subcellular localization of two licensing proteins, ORC2 and MCM7, in the mouse zygotes and two-cell embryos. In somatic cells ORC2 remains bound to DNA replication origins throughout the cell cycle, while MCM7 is one of the last proteins to bind to the licensing complex. We found that MCM7 but not ORC2 was bound to DNA in metaphase II oocytes and remained associated with the DNA until S-phase. Shortly after fertilization, ORC2 was detectable at the metaphase II spindle poles and then between the separating chromosomes. Neither protein was present in the sperm cell at fertilization. As the sperm head decondensed, MCM7 was bound to DNA, but no ORC2 was seen. By 4 h after fertilization, both pronuclei contained DNA bound ORC2 and MCM7. As expected, during S-phase of the first zygotic cell cycle, MCM7 was released from the DNA, but ORC2 remained bound. During zygotic mitosis, ORC2 again localized first to the spindle poles, then to the area between the separating chromosomes. ORC2 then formed a ring around the developing two-cell nuclei before entering the nucleus. Only soluble MCM7 was present in the G2 pronuclei, but by zygotic metaphase it was bound to DNA, again apparently before ORC2. In G1 of the two-cell stage, both nuclei had salt-resistant ORC2 and MCM7. These data suggest that licensing follows a unique pattern in the early zygote that differs from what has been described for other mammalian cells that have been studied.

Genome wide identification of promoter binding sites for H4K12ac in human sperm and its relevance for early embryonic development

Sperm chromatin reveals two characteristic features in that protamines are the predominant nuclear proteins and remaining histones are highly acetylated. Histone H4 acetylated at lysine 12 (H4K12ac) is localized in the post-acrosomal region, while protamine-1 is present within the whole nucleus. Chromatin immunoprecipitation in combination with promoter array analysis allowed genome-wide identification of H4K12ac binding sites. Previously, we reported enrichment of H4K12ac at CTCF binding sites and promoters of genes involved in developmental processes. Here, we demonstrate that H4K12ac is enriched predominantly between ± 2 kb from the transcription start site. In addition, we identified developmentally relevant H4K12ac-associated promoters with high expression levels of their transcripts stored in mature sperm. The highest expressed mRNA codes for testis-specific PHD finger protein-7 (PHF7), suggesting an activating role of H4K12ac in the regulatory elements of this gene. H4K12ac-associated genes revealed a weak correlation with genes expressed at 4-cell stage human embryos, while 23 H4K12ac-associated genes were activated in 8-cell embryo and 39 in the blastocyst. Genes activated in 4-cell embryos are involved in gene expression, histone fold and DNA-dependent transcription, while genes expressed in the blastocyst were classified as involved in developmental processes. Immunofluorescence staining detected H4K12ac from the murine male pronucleus to early stages of embryogenesis. Aberrant histone acetylation within developmentally important gene promoters in infertile men may reflect insufficient sperm chromatin compaction, which may result in inappropriate transfer of epigenetic information to the oocyte.

Blastomere removal from cleavage-stage mouse embryos alters steroid metabolism during pregnancy

Preimplantation genetic diagnosis (PGD) is a genetic screening of embryos conceived with assisted reproduction technologies (ART). A single blastomere from an early-stage embryo is removed and molecular analyses follow to identify embryos carrying genetic defects. PGD is considered highly successful for detecting genetic anomalies, but the effects of blastomere biopsy on fetal development are understudied. We aimed to determine whether single blastomere removal affects steroid homeostasis in the maternal-placental-fetal unit during mouse pregnancy. Embryos generated by in vitro fertilization (IVF) were biopsied at the four-cell stage, cultured to morula/early blastocyst, and transplanted into the oviducts of surrogate mothers. Nonbiopsied embryos from the same IVF cohorts served as controls. Cesarean section was performed at term, and maternal and fetal tissues were collected. Embryo biopsy affected the levels of steroids (estradiol, estrone, and progesterone) in fetal and placental compartments but not in maternal tissues. Steroidogenic enzyme activities (3beta-hydroxysteroid dehydrogenase, cytochrome P450 17alpha-hydroxylase, and cytochrome P450 19) were unaffected but decreased activities of steroid clearance enzymes (uridine diphosphate-glucuronosyltransferase and sulfotransferase) were observed in placentas and fetal livers. Although maternal body, ovarian, and placental weights did not differ, the weights of fetuses derived from biopsied embryos were lower than those of their nonbiopsied counterparts. The data demonstrate that blastomere biopsy deregulates steroid metabolism during pregnancy. This may have profound effects on several aspects of fetal development, of which low birth weight is only one. If a similar phenomenon occurs in humans, it may explain low birth weights associated with PGD/ART and provide a plausible target for improving PGD outcomes.

Viability of ICSI oocytes after caffeine treatment and sperm membrane removal with Triton X-100 in pigs

Non-adequate decondensation of injected sperm nucleus is one the main problems of intracytoplasmic sperm injection (ICSI) in porcine. With the aim of improving pronuclear formation, the effects on activation and embryo development rates of 0.1% Triton X-100 (TX) sperm pre-treatment for membrane removal and/or 5 mM Caffeine (CAF) addition in oocyte manipulating and culture medium for 2 h after ICSI or artificial activation were studied. The effects of 4 different Ca(2+) concentrations contained in the injection medium on embryo development after sham injection were also analysed. In Experiment 1, no significant effect on cleavage or blastocyst rate was detected independently of Ca(2+) concentration contained in the injection medium. In Experiment 2, oocytes injected with TX pre-treated sperm showed a significant higher rate of male pronuclear formation in comparison with oocytes from control group (2PN; 54.1 vs 36.6%). However, no differences on in vitro embryo development, cleavage or blastocyst rates were observed. In Experiment 3, oocytes treated with CAF during and after micromanipulation and injected with sperm pre-treated with TX had a significantly lower oocyte activation rate than any other experimental groups (25.7 vs 56.3-66.3%). No differences were observed in cleavage rates among different experimental groups. However, the CAF group showed a higher blastocyst rate significantly different from TX+CAF group (12.0 vs 1.9%, respectively). In a second approach, the effect of electric field strengths and CAF treatments on oocyte activation was studied. In Experiment 4, oocytes submitted to 0.6 kV/cm showed significant higher activation rates than 1.2 kV/cm ones regardless of the caffeine treatment (83.7 vs 55.9% and 75.7 vs 44.3%; in control and caffeine groups, respectively). No effect of caffeine treatment was observed in any experimental group. In conclusion, TX sperm treatment before ICSI without an additional activation procedure improved male pronuclear formation, but did not improve embryo development until blastocyst stage. No significant effect of caffeine was found when sperm was not treated with TX, although in membrane absence caffeine avoided oocyte activation and embryo development. Finally, caffeine had no effect on female pronuclear formation regardless of electric field strengths applied to the parthenogenetic activation.

Mouse females devoid of exposure to males during fetal development exhibit increased maternal behavior

Many sex differences can be found in the expression of aggression and parental nurturing behaviors. It is important to determine if these are modulated by prenatal conditions. Here, using assisted reproduction technologies, we generated females that were (mixed-sex) or were not (same-sex) exposed to males during fetal development, raised them by cross fostering among fosters' own female only pups to control for effects of postnatal environment, and compared their reproductive abilities and behavior. There were no differences between females from the two prenatal conditions in estrus cycle length and length of time spent at individual estrus cycle stages. Both types of females had similar ovulation efficiency and bred equally well yielding comparable litter size and progeny sex ratio. Females from the two prenatal conditions were also indistinguishable in social behavior and exhibited normal social responses towards unfamiliar females in the three-chamber social approach and social proximity tests. When urine was collected from both types of females and used as a point source in a scent-marking paradigm, exposed males showed a similar distribution and extent of urinary scent marking in response to urine from each type of female but tended to engage in higher durations of sniffing the urine from same-sex females. When females were tested in a resident-intruder paradigm 3 days after giving birth, same-sex females exhibited enhancement of pup grooming and an overall decrease of non-pup activity prior to male intruder introduction, and after introduction were more defensive as evidenced by higher rates of burying, open-mouth threat/lunges, and attacks towards the male, and decreased latencies to display these defensive behaviors. Our results suggest that females devoid of male exposure during fetal development have reproductive abilities similar to those of females from mixed-sex pregnancies, and have normal social interactions with other females. However, they exhibit hyper-maternal behavior both in terms of the care and defense of pups in front of a male intruder, and potentially produce a pheromonal milieu that renders them more attractive to males during olfactory investigations.