Activation of Toll-like receptor 7/8 encoded by the X chromosome alters sperm motility and provides a novel simple technology for sexing sperm

Expression of TLR7/8 in canine sperm and evaluation of the effect of ligand R848 on the sorting of canine X/Y sperm

The aim of this study was to analyze the expression pattern of Toll receptor 7/8 (TLR7/8) in canine sperm, and explore the feasibility of using TLR7/8 ligand resiquimod(R848)to separate canine X and Y sperm. In this study, cellular immunofluorescence was used to analyze the expression of TLR7/8 in canine sperm, real-time fluorescence quantitative PCR was used to calculate the proportion of X sperm in the lower layer of the incubation solution with R848 to evaluate the sorting effect of R848 on canine X/Y sperm, and sperm quality detection system was used to analyze the effect of R848 on the motility of canine sperm. The mechanism of effect of R848 on canine sperm motility was analyzed by Western blot. The results showed that TLR8 was not expressed in all canine sperm, while TLR7 was expressed in all canine sperm and was localized in the head and tail of sperm. When 0.4 μM R848 was incubated with canine sperm for 1 h, the total motility, average path velocity (VAP), average straight-line velocity (VSL), and average curved-line velocity (VCL) of canine sperm were significantly decreased(P < 0.05). There was no significant difference between the lower and upper layers of the R848 treatment group and the control group(P > 0.05), and the proportion of X sperm was nearly half. The levels of NF-κB and GSK3α/β phosphorylation of sperm in R848 treatment group were significantly increased compared with control group(P < 0.05). The above results showed that TLR7/8 was not differentially expressed in canine X and Y sperm. R848 could decrease the motility of canine spermatozoa and inhibit sperm motility by the GSK3α/β-hexokinase pathway through the phosphorylation of NFκB and GSK3α/β, while could not separate X and Y spermatozoa. The method of sorting X/Y sperm based on TLR7/8 is not feasible for dogs.

Reproductive Tract Mucus May Influence the Sex of Offspring in Cattle: Study in Cows That Have Repeatedly Calved Single-Sex Offspring

This study aimed to investigate the selective effect of the reproductive tract mucus in cows that have consistently produced offspring of a single sex on X/Y spermatozoa. We collected mucus from the reproductive tract of cows that had given calvings to offspring of the same sex, or alternated between sexes, for more than five consecutive calvings. We evaluated the pH of reproductive tract mucus. Subsequently, we conducted a spermatozoa penetration assay; the proportions of X and Y spermatozoa after penetration were then identified by dual TaqMan qPCR and flow cytometry. This was followed by in vitro fertilization and embryo sex determination experiments. Immediately afterwards, computer-aided spermatozoa analysis was employed to analyze the spermatozoa that had penetrated through different types of mucus in the reproductive tract. The analysis indicated that the reproductive tract mucus of cows consistently producing male or female calves exhibited selectivity towards X/Y spermatozoa. The differences in the pH values of the reproductive tract mucus among cows continuously producing male calves, those continuously producing female calves, and those alternately giving birth to male and female calves were not significant (p ≥ 0.05). The outcome of dual TaqMan qPCR for cows consistently producing male calves was Y: 79.29 ± 4.28% vs. X: 21.67 ± 4.53%; for cows consistently producing female calves, the equation was Y: 25.05 ± 4.88% vs. X: 75.34 ± 5.13%. The results of flow cytometry processing revealed the following proportions: for cows consistently producing male calves: Y: 83.33 ± 5.52% vs. X: 17.23 ± 4.74%; for cows consistently producing female calves: Y: 24.81 ± 4.13% vs. X: 76.64 ± 4.21%. The outcomes of embryo sex determination for cows consistently producing male calves were as follows: male embryos vs. female embryos (79.60 ± 2.87% vs. 21.07 ± 2.51%); for cows consistently producing female calves, the outcomes for male embryos vs. female embryos were 25.58 ± 3.96% vs. 75.63 ± 3.55%. Computer-aided analysis revealed that the concentration of spermatozoa penetrating the reproductive tract mucus in cows alternating between male and female calves (9.09 ± 0.72 million/mL) was significantly higher than that in cows consistently producing male calves (6.01 ± 1.19 million/mL) and cows consistently producing female calves (5.61 ± 0.60 million/mL). There were no significant differences in spermatozoa motility, the proportion of progressive motile spermatozoa, and curvilinear, straight-line, and average path velocities. Collectively, these findings indicate that the reproductive tract mucus of cows consistently producing offspring of a single sex exhibits selectivity towards either X or Y spermatozoa. This finding is of great significance for studying the impact of maternal factors on offspring sex.

Exploring aptamers for targeted enrichment of X sperm in bovine: unraveling selective potential

Nucleic acid aptamers have been used in the past for the development of diagnostic methods against a number of targets such as bacteria, pesticides, cancer cells etc. In the present study, six rounds of Cell-SELEX were performed on a ssDNA aptamer library against X-enriched sperm cells from Sahiwal breed cattle. Sequencing was used to examine the aptamer sequences that shown affinity for sperm carrying the X chromosome in order to find any possible X-sperm-specific sequences. Out of 35 identified sequences, 14 were selected based on bioinformatics analysis like G-Score and Mfold structures. Further validation of their specificity was done via fluorescence microscopy. The interaction of biotinylated-aptamer with sperm was also determined by visualizing the binding of streptavidin coated magnetic beads on the head region of the sperm under bright field microscopy. Finally, a real-time experiment was designed for the validation of X-sperm enrichment by synthesized aptamer sequences. Among the studied sequences, aptamer 29a exhibited a higher affinity for X sperm compared to Y sperm in a mixed population of sperm cells. By using aptamer sequence 29a, we obtained an enrichment of 70% for X chromosome bearing sperm cells.

Sex differences in genotype frequency and the risk of polycythemia associated with rs13419896 and rs2790859 among Tibetan highlanders living in Tsarang, Mustang, Nepal

BACKGROUND

Tibetan highlanders have adapted to hypoxic environments through genetic mechanisms that avoid hemoglobin concentration increases and prevent polycythemia. Recently, sex differences in hemoglobin dynamics with age have been reported among Tibetan highlanders living in Tsarang. Additionally, concerns have been raised that dietary changes associated with modernization may increase the risk of polycythemia and lifestyle-related diseases among Tibetan highlanders. However, the relationship between genetic polymorphisms and the risk of lifestyle-related diseases in Tibetan highlanders has been investigated in only a few regions. This study aims to elucidate whether polymorphisms in genes related to hypoxic adaptation are associated with the incidence of lifestyle-related diseases and polycythemia and whether these polymorphisms affect hemoglobin dynamics in the residents of Tsarang, Mustang, Nepal.

METHODS

Health checkup data from individuals living in Tsarang in Mustang District, Nepal, collected in 2017, were used to determine the prevalence of obesity, hypertension, diabetes, hypoxemia, and polycythemia. DNA was extracted from whole-blood samples, and data for the single-nucleotide polymorphisms (SNPs) rs13419896 (EPAS1), rs12619696 (EPAS1), and rs2790859 (EGLN1) were obtained using real-time PCR. The health checkup data were statistically analyzed to determine the associations of these diseases with polymorphisms in genes related to hypoxic adaptation.

RESULTS

A total of 168 participants, comprising 78 males and 90 females, were included in the final analysis. In terms of the prevalence of each disease, only the prevalence of polycythemia significantly differed between sexes (p < 0.01). Additionally, among the three analyzed SNPs, significant sex differences in genotype frequency were observed for rs13419896 and rs2790859. For rs2790859 in females, Tibetan highlanders with the adaptive genotype had a significantly lower incidence of polycythemia (p < 0.01) and significantly lower hemoglobin concentrations (p < 0.01).

CONCLUSIONS

This study revealed that there are sex differences in the genotype frequency of gene-related hypoxic adaptations among the residents of Tsarang. The findings also suggested that the rs2790859 polymorphism might be involved in the recent incidence of polycythemia among Tsarang residents. If the frequency of non-Tibetan genotypes increases due to intermixing with other populations in the Mustang District, polycythemia may emerge as a modern disease. It is essential to continue investigating the health status of Mustang residents to elucidate various aspects of hypoxic adaptation and disease susceptibility.

DCAF2 regulates the proliferation and differentiation of mouse progenitor spermatogonia by targeting p21 and thymine DNA glycosylase

DDB1-Cullin-4-associated factor-2 (DCAF2, also known as DTL or CDT2), a conserved substrate recognition protein of Cullin-RING E3 ligase 4 (CRL4), recognizes and degrades several substrate proteins during the S phase to maintain cell cycle progression and genome stability. Dcaf2 mainly expressed in germ cells of human and mouse. Our study found that Dcaf2 was expressed in mouse spermatogonia and spermatocyte. The depletion of Dcaf2 in germ cells by crossing Dcaf2fl/fl mice with stimulated by retinoic acid gene 8(Stra8)-Cre mice caused a reduction in progenitor spermatogonia and differentiating spermatogonia, eventually leading to the failure of meiosis initiation and male infertility. Further studies showed that depletion of Dcaf2 in germ cells caused abnormal accumulation of the substrate proteins, cyclin-dependent kinase inhibitor 1A (p21) and thymine DNA glycosylase (TDG), decreasing of cell proliferation, increasing of DNA damage and apoptosis. Overexpression of p21 or TDG attenuates proliferation and increases DNA damage and apoptosis in GC-1 cells, which is exacerbated by co-overexpression of p21 and TDG. The findings indicate that DCAF2 maintains the proliferation and differentiation of progenitor spermatogonia by targeting the substrate proteins p21 and TDG during the S phase.

The effect of toll-like receptor 7/8 ligand in inhibiting the motility of putative X-chromosome-bearing sperm in rams

Objectives

This study aims to determine the effect of a toll-like receptor 7/8 (TLR7/8) ligand on the motility of putative X- and Y-chromosome-bearing sperm in rams.

Materials and Methods

Sperm from three fertile rams were incubated with tris-citrate buffer containing 0 to 0.9 μM resiquimod (a TLR7/8 ligand) that affects only the X chromosome sperm. Sperm was then subjected to a swim-up test method. After incubation, sperm in the top and lower layers of the media were transferred into a separate new tube. Sperm motility characteristics, concentration, morphometry, and adenosine triphosphate (ATP) concentration from both layers were identified. The data were analyzed for multiple comparisons using one-way analysis of variance.

Results

The study demonstrated that the presence of resiquimod used in the swim-up method facilitated the morphometric separation of smaller sperm, predominantly representing Y chromosome sperm in the top layer. Meanwhile, larger samples, indicating X chromosome sperm, accumulated in the lower layer of the media, thus increasing sperm concentration. Resiquimod also decreased motility in the lower layer, but samples in the top layer were unaffected. This decrease was reinforced by the depletion of the ATP level of sperm at the lower level.

Conclusion

The TLR7/8 ligand reduced the motility of the putative X-sperm by decreasing their ATP content, allowing separation from the putative Y-sperm. These results suggested the importance of TLR7/8 as a potential biomarker in sperm selection technology.

In vitro characteristics of X- and Y-bearing ram spermatozoa sorted by bovine serum albumin (BSA) column and TLR7/8 ligand R848

The quality of the separated fractions in sex-sorted semen is very important for the success of the artificial insemination. This study aimed to evaluate some in vitro characteristics (DNA quantity, kinematic parameters and enzymes activity) of X- and Y-bearing ram spermatozoa sorted by bovine serum albumin (BSA) column and toll-like receptors (TLR)7/8 ligand R848. The ejaculates from six rams were collected by artificial vagina and subjected to a computer-assisted semen analysis (CASA). Total motility and percentage of the sperms with rapid and medium progressivity or non-progressivity in whole ejaculates and in X and Y fractions were analyzed. Activity of the enzymes ALP, GGT, CK, LDH and accumulation of lactate in the seminal plasma of ejaculates and in the environmental fluid of sexed spermatozoa were measured by biochemical analyzer. DNA was isolated from precipitated spermatozoa, and its quantity was measured. For both protocols the DNA mass from X-bearing fractions was higher, than from Y-bearing fractions. The high total motility of X- and Y-bearing spermatozoa as well as greater percent sperms with progressive motility were observed after use of BSA protocol. The application of TLR7/8 ligand R848 protocol led to reducing of Y-sperm motility and enhancement of non-progressivity in both fractions, which corresponded to the determined high amount of the extracellular lactate. For both methods, the significantly reduced activity of enzymes in the X and Y spermatozoa environmental fluids was established. Both protocols produce X- and Y-sperm fractions with satisfactory quality (over 80% total motility and over 50% rapid and medium progressive spermatozoa in each fraction).

Semen sexing and its impact on fertility and genetic gain in cattle

Semen sexing is among one of the most remarkable inventions of the past few decades in the field of reproductive biotechnology. The urge to produce offspring of a desired sex has remained since traditional times. Researchers have tried many methods for accurate semen sexing, but only the flow cytometry method has proved to be effective for commercial utilization. However, there were always concerns about the effects of sexed semen, especially on fertility and the rate of genetic gain. Some concerns were genuine because of factors such as low semen dosage in sexed semen straws and damage to sperm during the sorting process. Various researchers have conducted numerous studies to find out the effect of sexed semen on fertility and, in this article, we reflect on their findings. Initially, there were comparatively much lower conception rates (∼70% of conventional semen) but, with refinement in technology, this gap is bridging and the use of sexed semen will increase over time. Concerning genetic gain with use of sexed semen, a positive effect on rate of genetic progress with the use of sexed semen has been observed based on various simulation studies, although there has been a mild increase in inbreeding.

Sperm Toolbox-A selection of small molecules to study human spermatozoa

Male contraceptive options and infertility treatments are limited, and almost all innovation has been limited to updates to medically assisted reproduction protocols and methods. To accelerate the development of drugs that can either improve or inhibit fertility, we established a small molecule library as a toolbox for assay development and screening campaigns using human spermatozoa. We have profiled all compounds in the Sperm Toolbox in several automated high-throughput assays that measure stimulation or inhibition of sperm motility or the acrosome reaction. We have assayed motility under non-capacitating and capacitating conditions to distinguish between pathways operating under these different physiological states. We also assayed cell viability to ensure any effects on sperm function are specific. A key advantage of our studies is that all compounds are assayed together in the same experimental conditions, which allows quantitative comparisons of their effects in complementary functional assays. We have combined the resulting datasets to generate fingerprints of the Sperm Toolbox compounds on sperm function. The data are included in an on-line R-based app for convenient querying.

Gender Control of Mouse Embryos by Activation of TLR7/8 on X Sperm via Ligands dsRNA-40 and dsRNA-DR

Gender control technologies are promising for enhancing the production efficiency of the farm animal industry, and preventing sex-linked hereditary diseases in humans. It has been shown that the X sperm of mammalian animals specifically expresses X-chromosome-derived toll-like receptor 7/8 (TLR7/8), and the activation of TLR7/8 on the X sperm by their agonist, R848, can separate X and Y sperm via the specific inhibition of X sperm motility. The use of R848-preselected sperm for fertilization resulted in sex-ratio-skewed embryos or offspring. In this study, we aimed to investigate whether two other TLR7/8 ligands, double-stranded RNA-40 (dsRNA-40) and double-stranded RNA-DR (dsRNA-DR), are also effective in the separation of mouse X and Y sperm and the subsequent generation of gender-ratio-skewed in vitro fertilization (IVF) embryos. Our results indicated that cholesterol modification significantly enhances the transfection of dsRNA-40 and dsRNA-DR into sperm cells. dsRNA-40 and dsRNA-DR incubation with mouse sperm could separate X and Y sperm by the specific suppression of X sperm motility by decreasing its ATP level and mitochondrial activity. The use of a dsRNA-40- or dsRNA-DR-preselected upper layer of sperm, which predominantly contains high-motility Y sperm, for IVF caused a male-biased sex ratio shift in resulting embryos (with 65.90-74.93% of embryos being male). This study develops a simple new method for the efficient separation of mammalian X and Y sperm, enabling the selective production of male or female progenies.

A Single-Step Genome-Wide Association Study for Semen Traits of Egyptian Buffalo Bulls

The present study aimed to contribute to the limited research on buffalo (Bubalus bubalis) semen traits by incorporating genomic data. A total of 8465 ejaculates were collected. The genotyping procedure was conducted using the Axiom® Buffalo Genotyping 90 K array designed by the Affymetrix Expert Design Program. After conducting a quality assessment, we utilized 67,282 SNPs genotyped in 192 animals. We identified several genomic loci explaining high genetic variance by employing single-step genomic evaluation. The aforementioned regions were located on buffalo chromosomes no. 3, 4, 6, 7, 14, 16, 20, 22, and the X-chromosome. The X-chromosome exhibited substantial influence, accounting for 4.18, 4.59, 5.16, 5.19, and 4.31% of the genomic variance for ejaculate volume, mass motility, livability, abnormality, and concentration, respectively. In the examined genomic regions, we identified five novel candidate genes linked to male fertility and spermatogenesis, four in the X-chromosome and one in chromosome no. 16. Additional extensive research with larger sample sizes and datasets is imperative to validate these findings and evaluate their applicability for genomic selection.

Pre-implantation development of cattle embryos produced from fresh bull semen enriched for X- chromosome-bearing spermatozoa using a monoclonal antibody

Immunological approaches are gaining attention as a convenient and economical method for sex-sorting mammalian spermatozoa. A monoclonal antibody (WholeMom™) has previously been reported to cause agglutination of Y-chromosome-bearing spermatozoa in frozen-thawed semen for gender preselection. However, its usefulness for gender preselection in fresh semen and subsequent in vitro fertilization (IVF) after freeze-thawing has not been reported. This study investigated the in vitro development of cattle embryos produced from fresh bull semen pre-treated with WholeMom™ monoclonal antibody. Results showed that antibody-treated, non-agglutinated spermatozoa (presumably X-chromosome-bearing spermatozoa) could fertilize cattle oocytes in vitro. However, embryos generated from non-agglutinated (enriched in X-chromosome-bearing spermatozoa) had a lower (p < 0.05) ability to cleave (66.4 ± 2.5% vs. 75.1 ± 3.3%) than those of non-treated control sperm. Nevertheless, the percentage of blastocysts developed from cleaved embryos did not differ (p > 0.05) between the groups (34.8 ± 3.7% vs. 35.8 ± 3.4%). Duplex PCR of blastocysts, using a bovine-specific universal primer pair and a Y-chromosome-specific primer pair, showed a sex ratio of 95.8% females from sex-sorted spermatozoa, which was higher than those of non-treated control spermatozoa (46.4%). In conclusion, the results of the present study suggest that monoclonal antibody-based enrichment of X- chromosome-bearing spermatozoa can be applied to fresh bull semen without compromising their post-fertilization early embryonic development to the blastocyst stage. Future studies should investigate the term development and sex ratio of calves from antibody-treated spermatozoa.

The History and Prospects of Rabbit Sperm Sexing

Sperm sex selection is a longstanding challenge in the field of animal reproduction. The cuniculture industry, in particular producers of males or females for breeding purposes, would greatly benefit from the pre-selection of the offspring's sex. This review article overviews the current and future developments in rabbit sperm sexing technologies, as well as the implications of implementing these methodologies in cuniculture. The first attempts of sperm sexing were performed in rabbits; however, a both efficient and cost-effective methodology was not yet developed for this species. Those included sperm sexing according to differences in sperm density, surface electric charge, pH susceptibility, antisera reaction, and flow cytometry. Separation by flow cytometry has proven to be efficient in rabbits, yielding fractions with approximately 81% and 86% purity for X- and Y-sperm, respectively. However, it is not cost-effective for cuniculture and decreases sperm quality. The advantages, limitations, and practical considerations of each method are presented, highlighting their applicability and efficiency. Furthermore, herein we explore the potential of immunological-based techniques that overcome some of the limitations of earlier methods, as well as recent advancements in sperm sexing technologies in other animal models, which could be applied to rabbits. Finally, the challenges associated with the development and widespread implementation of rabbit sperm sexing technologies are addressed. By understanding the advantages and limitations of existing and emerging methods, researchers can direct their efforts towards the most promising directions, ultimately contributing to a more efficient, profitable, and sustainable cuniculture.

Pregnancy bias toward boys or girls: The Japan Environment and Children's Study

The sex of the conceived child is a significant concern for parents. To verify whether there women have pregnancy bias toward boys or girls, we investigated whether the history of continuous same-sex pregnancy was associated with the subsequent child's sex. We prospectively analyzed data from the Japan Environment and Children's Study, a birth cohort study. We included all cases of singleton live births (n = 98 412). Women with pregnancy due to infertility treatment were excluded (n = 6255); Similarly, women with a history of miscarriage, artificial abortion, stillbirth, and multiple pregnancies, and those with missing data on the sex of the previous child were excluded. Altogether, 62 718 women were included. For the first live birth, a male-biased sex ratio of 1.055 was observed. Further, no significant difference was found in the sex ratio of the conceived child between women with one boy and those with one girl previously. However, when there were more than two children previously, the subsequently conceived child's male/female sex ratio was significantly higher among boy-only mothers than among girl-only mothers. The results indicated that several pregnant women are biased toward conceiving either boys or girls.

Biochemical Features of X or Y Chromosome-Bearing Spermatozoa for Sperm Sexing

This review presents information on biochemical features of spermatozoa bearing X or Y chromosome, enabling production of a sperm fraction with pre-defined sex chromosome. The almost only technology currently used for such separation (called sexing) is based on the fluorescence-activated cell sorting of sperm depending on DNA content. In addition to the applied aspects, this technology made it possible to analyze properties of the isolated populations of spermatozoa bearing X or Y chromosome. In recent years, existence of the differences between these populations at the transcriptome and proteome level have been reported in a number of studies. It is noteworthy that these differences are primarily related to the energy metabolism and flagellar structural proteins. New methods of sperm enrichment with X or Y chromosome cells are based on the differences in motility between the spermatozoa with different sex chromosomes. Sperm sexing is a part of the widespread protocol of artificial insemination of cows with cryopreserved semen, it allows to increase proportion of the offspring with the required sex. In addition, advances in the separation of X and Y spermatozoa may allow this approach to be applied in clinical practice to avoid sex-linked diseases.

Diluent pH affects sperm motility via GSK3 α/β-hexokinase pathway for the efficient enrichment of X-sperm to increase the female kids rate of dairy goats

Dairy goats are the goats bred with the ability to produce large quantities of milk, and the increase of the female kid rate of breeding dairy goats is beneficial for milk production and economic benefits of dairy goat farms. Our previous study revealed that regulating the pH of dairy goat semen diluent to 6.2 or 7.4 respectively, the proportion of X chromosome bearing sperm (X-sperm) in the up and down layers of the tube after incubation was significantly higher than that of Y chromosome bearing sperm (Y-sperm) i.e. enriched X-sperm. In this study, fresh dairy goat semen collected in different seasons was diluted in different pH solutions to calculate the number and rate of X-sperm and to measure the functional parameters of enriched sperm. The artificial insemination experiments were performed with enriched X-sperm. The mechanisms of regulating the pH of diluent affecting sperm enrichment were further studied. The results showed that the proportion of enriched X-sperm in pH 6.2 and 7.4 diluents of sperm collected in different seasons showed no significantly different, but were significantly higher than that of the control group (pH 6.8). The in vitro functional parameters of X-sperm enriched in pH 6.2 and 7.4 diluent solution were not significantly different from those of the control group (P > 0.05). After artificial insemination with X-sperm enriched in pH7.4 diluent, the proportion of female offspring was significantly higher than that of the control group. It was found that the regulating pH of the diluent affected sperm mitochondrial activity and glucose uptake capacity via phosphorylating NF-κB and GSK3α/β proteins. The motility activity of X-sperm was enhanced under acidic conditions and weakened under alkaline conditions, which was conducive to the effective enrichment of X-sperm. This study demonstrated that the number and proportion of X-sperm enriched using pH 7.4 diluent were elevated, and the proportion of female kids was increased. This technology can be used for the reproduction and production of dairy goats in farms at large scales.

TLR7/8 agonist (R848) inhibit bovine X sperm motility via PI3K/GSK3α/β and PI3K/NFκB pathways

Sex-control technology have great economic value and is one of the hot topics in livestock research. To produce more milk, dairy farmers prefer female offspring. X/Y sperm separation is an effective method for offspring sex control. Currently, the major commercial production method for sperm separation is flow cytometry sorting in cattle. However, flow cytometry requires expensive equipment and long sorting times. So, a simple and inexpensive method for producing a higher number of dairy cows is required. In this study, R848 activates toll-like receptor 7/8 (TLR7/8), thereby separating X from Y sperm. The results showed TLR7/8 is expressed in the tail of X sperm. Immunofluorescence (IF) of testes, epididymis, and ejaculate shows that the number of TLR7⁺/8⁺ sperm cells is up to 50 %. Furthermore, TLR7/8 agonist (R848) affects mitochondrial function through the PI3K/GSK3α/β/hexokinase and PI3K/NFκB/hexokinase signalling pathways, inhibiting X sperm motility, while the motility of Y-sperm remains unchanged. The difference in sperm motility causes Y sperm (with high motility) to move to the upper layer and X-sperm (with low motility) to the lower layer allowing the separation of X and Y sperm. Based on this study, we reveal a simple and effective method for enriched X/Y sperms from cattle.

The reproductive success of Simmental bovine after sex-sorting under various incubation and centrifugation protocols

Background and Aim: To enhance the reproductive potential and increase productivity and population of cows, spermatozoa sex-sorting technology is required. This study aimed to examine the effect of sexing sperm, separated using a bovine serum albumin (BSA) column with varying incubation durations and centrifugation methods, for successful artificial insemination. Materials and Methods: Six Simmental bulls and 30 cows (n = 30) as the recipients were selected for this study at Balai Pembibitaan Hijauan Pakan Ternak Sembawa Indonesia. The study parameters included sperm motility, viability, plasma membrane integrity, and conception rate (CR). The experiment was divided into three protocols to find out differences in some parameters: (1) BSA incubation time effect (P) with P1 (40 min), P2 (50 min), and P3 (60 min); (2) freezing time effect with before freezing and after-thawing treatments; and (3) CR determined by measuring the proportion of pregnant cows following insemination with non-sexed, X-bearing, and Y-bearing sperms without centrifugation (n = 15) (A0, A1, and A2) and with centrifugation (n = 15) (B0, B1, and B2) in the acquired data, which were counted using the Statistical Package for the Social Sciences version 21 program. Analysis of variance was utilized to evaluate all treatments at various levels. Results: The results demonstrated that centrifugation time influenced all sperm quality metrics for sperm containing X and Y (p < 0.05). The non-return rate (NRR) of non-sexed frozen semen, both centrifuged (A0) and not centrifuged (B0), was more significant than frozen semen produced by sexing X and Y spermatozoa. The NRR indicated a value of 80% based on the number of lactating cows. Conclusion: Bovine serum albumin incubation and centrifugation protocols influenced and decreased all sperm quality indicators throughout the sexing procedure and could still be used as a sexing protocol. Furthermore, regarding NRR and service per conception, non-sexual treatment is superior to sexing treatment. Keywords: bovine serum albumin, centrifugated, conception rate, incubation, sexing, sperm.

Bypassing Mendel's First Law: Transmission Ratio Distortion in Mammals

Mendel's law of segregation states that the two alleles at a diploid locus should be transmitted equally to the progeny. A genetic segregation distortion, also referred to as transmission ratio distortion (TRD), is a statistically significant deviation from this rule. TRD has been observed in several mammal species and may be due to different biological mechanisms occurring at diverse time points ranging from gamete formation to lethality at post-natal stages. In this review, we describe examples of TRD and their possible mechanisms in mammals based on current knowledge. We first focus on the differences between TRD in male and female gametogenesis in the house mouse, in which some of the most well studied TRD systems have been characterized. We then describe known TRD in other mammals, with a special focus on the farmed species and in the peculiar common shrew species. Finally, we discuss TRD in human diseases. Thus far, to our knowledge, this is the first time that such description is proposed. This review will help better comprehend the processes involved in TRD. A better understanding of these molecular mechanisms will imply a better comprehension of their impact on fertility and on genome evolution. In turn, this should allow for better genetic counseling and lead to better care for human families.

Sexually Dimorphic Gene Expression in X and Y Sperms Instructs Sexual Dimorphism of Embryonic Genome Activation in Yellow Catfish (Pelteobagrus fulvidraco)

Paternal factors play an important role in embryonic morphogenesis and contribute to sexual dimorphism in development. To assess the effect of paternal DNA on sexual dimorphism of embryonic genome activation, we compared X and Y sperm and different sexes of embryos before sex determination. Through transcriptome sequencing (RNA-seq) and whole-genome bisulfite sequencing (WGBS) of X and Y sperm, we found a big proportion of upregulated genes in Y sperm, supported by the observation that genome-wide DNA methylation level is slightly lower than in X sperm. Cytokine-cytokine receptor interaction, TGF-beta, and toll-like receptor pathways play important roles in spermatogenesis. Through whole-genome re-sequencing (WGRS) of parental fish and RNA-seq of five early embryonic stages, we found the low-blastocyst time point is a key to maternal transcriptome degradation and zygotic genome activation. Generally, sexual differences emerged from the bud stage. Moreover, through integrated analysis of paternal SNPs and gene expression, we evaluated the influence of paternal inheritance on sexual dimorphism of genome activation. Besides, we screened out gata6 and ddx5 as potential instructors for early sex determination and gonad development in yellow catfish. This work is meaningful for revealing the molecular mechanisms of sex determination and sexual dimorphism of fish species.

Mysteries and unsolved problems of mammalian fertilization and related topics

Mammalian fertilization is a fascinating process that leads to the formation of a new individual. Eggs and sperm are complex cells that must meet at the appropriate time and position within the female reproductive tract for successful fertilization. I have been studying various aspects of mammalian fertilization over 60 years. In this review, I discuss many different aspects of mammalian fertilization, some of my laboratory's contribution to the field, and discuss enigmas and mysteries that remain to be solved.

Advancements in mammalian X and Y sperm differences and sex control technology

Mammal sex determination depends on whether the X sperm or Y sperm binds to the oocyte during fertilization. If the X sperm joins in oocyte, the offspring will be female, if the Y sperm fertilizes, the offspring will be male. Livestock sex control technology has tremendous value for livestock breeding as it can increase the proportion of female offspring and improve the efficiency of livestock production. This review discusses the detailed differences between mammalian X and Y sperm with respect to their morphology, size, and motility in the reproductive tract and in in vitro conditions, as well as ’omics analysis results. Moreover, research progress in mammalian sex control technology has been summarized.

The enriched Y-bearing sperm combined with delayed fixed-time artificial insemination for obtaining male Simmental crossbred offspring

Background and Aim:

The production of male calf beef cattle is an agricultural innovation needed to increase the farm’s productivity as a provider of meat sources. This study aimed to determine the sex ratio of the offspring of cows inseminated with Y-bearing sperm enriched by Percoll density gradient centrifugation and swim-up, combined with delayed fixed-time artificial insemination (FTAI).

Materials and Methods:

Ejaculates of Simmental bulls were divided into four equal portions and grouped as T0 (control, non-sexed semen), T1 and T2 were sexed semen using Percoll density gradient centrifugation three and five levels, respectively, and T3 was sexed semen using swim-up. After the sex was sorted, the semen was diluted in a tris-egg yolk extender, packaged in French mini-straws containing 50 million live sperm cells, and frozen. Pre-sexed, post-sexed, and post-thawed spermatozoa were evaluated based on progressive motility, viability, intact plasma membrane, and abnormality. The post-thawed semen of T0 was artificially inseminated to recipient cows at 12 h after onset of estrus (not delayed FTAI). Meanwhile, the delayed FTAI was conducted 18-20 h after onset of estrus using the T0, the best of T1 and T2, and the T3 post-thawed semen.

Results:

The Percoll density gradient centrifugation reduced motility, viability, and intact plasma membrane but increased sperm abnormalities. Meanwhile, the swim-up process increased motility, viability, and intact plasma membrane of sperm cells but decreased sperm abnormalities. Post-thawed semen decreased motility, viability, and intact plasma membrane of sperm cells but increased sperm abnormalities. The sex ratio of the Simmental crossbred offspring was 96.08% and 100% in T1 and T3, respectively, compared to 48.25% and 67.39% in T0 not delayed and delayed FTAI, respectively.

Conclusion:

The Percoll density gradient centrifugation and swim-up methods are prospective for obtaining male offspring.

Sperm bauplan and function and underlying processes of sperm formation and selection

The spermatozoon is a highly differentiated and polarized cell, with two main structures: the head, containing a haploid nucleus and the acrosomal exocytotic granule, and the flagellum, which generates energy and propels the cell; both structures are connected by the neck. The sperm's main aim is to participate in fertilization, thus activating development. Despite this common bauplan and function, there is an enormous diversity in structure and performance of sperm cells. For example, mammalian spermatozoa may exhibit several head patterns and overall sperm lengths ranging from ∼30 to 350 µm. Mechanisms of transport in the female tract, preparation for fertilization, and recognition of and interaction with the oocyte also show considerable variation. There has been much interest in understanding the origin of this diversity, both in evolutionary terms and in relation to mechanisms underlying sperm differentiation in the testis. Here, relationships between sperm bauplan and function are examined at two levels: first, by analyzing the selective forces that drive changes in sperm structure and physiology to understand the adaptive values of this variation and impact on male reproductive success and second, by examining cellular and molecular mechanisms of sperm formation in the testis that may explain how differentiation can give rise to such a wide array of sperm forms and functions.

Sex ratio imbalance following blastocyst transfer is associated with ICSI but not with IVF: an analysis of 14,892 single embryo transfer cycles

PURPOSE

Assisted reproductive technology (ART) has an impact on secondary sex ratio (SSR), which is seemed to be elevated after blastocyst transfer (BT) but decreased following ICSI procedure. We aim to assess whether the higher SSR associated with BT could be influenced by fertilization method used.

METHODS

All consecutive IVF/ICSI cycles (fresh and frozen) involving single embryo transfer (SET) resulting in a live birth between 2015 and 2019 were retrospective analyzed. Logistic regression was used to model the effect on the SSR of maternal and specific ART characteristics.

RESULTS

Six thousand nine hundred twenty-two women were included with the crude SSR of 54.8%. The impact of BT on SSR is influenced by the fertilization method used. After adjustment for potential confounders, the SSR in the ICSI BT group was significantly higher when compared to ICSI cleavage-stage embryo SET (aOR 1.24; 95% CI 1.10-1.40, P < 0.001). However, this effect was not detected among SBT with IVF treatment (aOR 1.04; 95% CI 0.97-1.12, P = 0.260). Assessing blastocyst morphological parameters, high trophectoderm quality was significantly associated with elevated SSR (aOR 1.76, 95% CI 1.34-2.31 [A vs. C], and aOR 1.28, 95% CI 1.14-1.44 [B vs. C]). No significant difference was shown in expansion, inner cell mass, or days of blastocyst formation between male and female blastocysts.

CONCLUSIONS

The impact of BT on SSR could be influenced by the fertilization method used. The higher SSR was observed after BT with ICSI procedures but not with IVF. Interpretation of the findings is limited by the potential for selection and confounding bias.

Cell-Specific Expression Pattern of Toll-Like Receptors and Their Roles in Animal Reproduction

Toll-like receptors (TLRs), a part of the innate immune system, have critical roles in protection against infections and involve in basic pathology and physiology. Secreted molecules from the body or pathogens could be a ligand for induction of the TLR system. There are many immune and non-immune types of cells that express at a least single TLR on their surface or cytoplasm. Those cells may be a player in a defense system or in the physiological regulation mechanisms. Reproductive tract and organs contain different types of cells that have essential functions such as hormone production, providing an environment for embryo/fetus, germ cell production, etc. Although lower parts of reproductive organs are in a relationship with outsider contaminants (bacteria, viruses, etc.), upper parts should be sterile to provide a healthy pregnancy and germ cell production. In those areas, TLRs bear controller or regulator roles. In this chapter, we will provide current information about physiological functions of TLR in the cells of the reproductive organs and tract, and especially about their roles in follicle selection, maturation, follicular atresia, ovulation, corpus luteum (CL) formation and regression, establishment and maintenance of pregnancy, sperm production, maturation, capacitation as well as the relationship between TLR polymorphism and reproduction in domestic animals. We will also discuss pathogen-associated molecular patterns (PAMPs)-induced TLRs that involve in reproductive inflammation/pathology.

TLR7/8 signalling affects X-sperm motility via the GSK3 α/β-hexokinase pathway for the efficient production of sexed dairy goat embryos

Background

Goat milk is very similar to human milk in terms of its abundant nutrients and ease of digestion. To derive greater economic benefit, farmers require more female offspring (does); however, the buck-to-doe offspring sex ratio is approximately 50%. At present, artificial insemination after the separation of X/Y sperm using flow cytometry is the primary means of controlling the sex of livestock offspring. However, flow cytometry has not been successfully utilised for the separation of X/Y sperm aimed at sexing control in dairy goats.

Results

In this study, a novel, simple goat sperm sexing technology that activates the toll-like receptor 7/8 (TLR7/8), thereby inhibiting X-sperm motility, was investigated. Our results showed that the TLR7/8 coding goat X-chromosome was expressed in approximately 50% of round spermatids in the testis and sperm, as measured from cross-sections of the epididymis and ejaculate, respectively. Importantly, TLR7/8 was located at the tail of the X-sperm. Upon TLR7/8 activation, phosphorylated forms of glycogen synthase kinase α/β (GSK3 α/β) and nuclear factor kappa-B (NF-κB) were detected in the X-sperm, causing reduced mitochondrial activity, ATP levels, and sperm motility. High-motility Y-sperm segregated to the upper layer and the low-motility X-sperm, to the lower layer. Following in vitro fertilisation using the TLR7/8-activated sperm from the lower layer, 80.52 ± 6.75% of the embryos were XX females. The TLR7/8-activated sperm were subsequently used for in vivo embryo production via the superovulatory response; nine embryos were collected from the uterus of two does that conceived. Eight of these were XX embryos, and one was an XY embryo.

Conclusions

Our study reveals a novel TLR7/8 signalling mechanism that affects X-sperm motility via the GSK3 α/β-hexokinase pathway; this technique could be used to facilitate the efficient production of sexed dairy goat embryos.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00613-y.

Individual variation of the percentage of Y-chromosome bearing sperm content in human ejaculates

The study aimed to determine the variation of Y-chromosome-bearing sperm content among individual ejaculates. A real-time polymerase chain reaction (qPCR) with unique primers was developed and used to calculate the percentage of Y-chromosome-bearing sperm in individual ejaculates from 50 randomly selected men. There was a significant difference in the overall mean ± SD between the proportion of Y-chromosome-bearing sperm and X-chromosome-bearing sperm (45.36 ± 7.88 vs. 54.42 ± 7.88). Of the 50 ejaculates, 17 had more than, and 14 had less than the 99% confidence interval of the mean of the Y-chromosome-bearing sperm (45.58 ± 2.87). These results suggest that the inconsistency in sperm-based sex-selection outcomes appears to be a function of differences in the ejaculates and highlights the need for further study in environmental and genetic factors contributing to X or Y bearing spermatozoan instability.Abbreviations: qPCR: real-time polymerase chain reaction; ROS: reactive oxygen species; DTT: dithiothreitol; SRY: sex-determining region Y.

Saturated fatty acids accelerate linear motility through mitochondrial ATP production in bull sperm

PURPOSE

The present study was undertaken to clarify whether bovine sperm could take up fatty acids (FAs) and produce ATP to maintain linear motility.

METHODS

Frozen bovine semen was thawed in media containing either lipid mixture (LM) or FAs, and sperm motility was analyzed. The kinetic changes in FA levels in sperm were detected using gas chromatography-mass spectrometry. The mitochondrial activity of sperm thawed in media containing LM or FAs was analyzed based on the fluorescence intensity of JC-1 staining and the oxygen consumption rate. FA transporters were observed using whole-mounted immunofluorescence.

RESULTS

Sperm linear motility was significantly (P < .05) increased after thawing in media with LM and FA. Moreover, saturated fatty acids were predominant in sperm thawed in media with LM. Notably, our study revealed that frozen bovine sperm possessed FA transporters in the midpiece where the fluorescence signals were detected after treatment with fluorescence-tagged FA. Treatment with FA activated electron transport in mitochondria through β-oxidation.

CONCLUSIONS

Sperm linear motility is facilitated by FAs in the thawing media used for frozen bovine sperm. This might provide a new approach for upgrading the artificial insemination technique used in both livestock animals and human infertility care.

Bovine semen sexing: Sperm membrane proteomics as candidates for immunological selection of X- and Y-chromosome-bearing sperm

The use of sexed semen in dairy and beef farms ensures the production of animals of the desired sex, resulting in a reduction of costs and an improvement of environmental sustainability. Several methods have been developed over the years, but most of them were abandoned due to their limited efficacy. Currently, the only commercially available method for the separation of X- and Y-chromosome-bearing sperm is fluorescence-activated cell sorting. However, this technique is expensive and has limited usefulness for the industry, considering that it cannot produce doses of sexed semen with the desired number of sperm for artificial insemination. Immunological methods have emerged as an attractive alternative to flow cytometry and proteomic knowledge of X- and Y-sperm could be useful to the development of a new method. In this review, we identify the main applications of sexed semen, describe the existing methods and highlight future research opportunities in the field. We consider that immunological methods, based on sperm cell's surface proteins differentially expressed between X- and Y-sperm, could be an interesting and promising approach to semen sexing.

Battle of the Sex Chromosomes: Competition between X and Y Chromosome-Encoded Proteins for Partner Interaction and Chromatin Occupancy Drives Multicopy Gene Expression and Evolution in Muroid Rodents

Transmission distorters (TDs) are genetic elements that favor their own transmission to the detriments of others. Slx/Slxl1 (Sycp3-like-X-linked and Slx-like1) and Sly (Sycp3-like-Y-linked) are TDs, which have been coamplified on the X and Y chromosomes of Mus species. They are involved in an intragenomic conflict in which each favors its own transmission, resulting in sex ratio distortion of the progeny when Slx/Slxl1 versus Sly copy number is unbalanced. They are specifically expressed in male postmeiotic gametes (spermatids) and have opposite effects on gene expression: Sly knockdown leads to the upregulation of hundreds of spermatid-expressed genes, whereas Slx/Slxl1-deficiency downregulates them. When both Slx/Slxl1 and Sly are knocked down, sex ratio distortion and gene deregulation are corrected. Slx/Slxl1 and Sly are, therefore, in competition but the molecular mechanism remains unknown. By comparing their chromatin-binding profiles and protein partners, we show that SLX/SLXL1 and SLY proteins compete for interaction with H3K4me3-reader SSTY1 (Spermiogenesis-specific-transcript-on-the-Y1) at the promoter of thousands of genes to drive their expression, and that the opposite effect they have on gene expression is mediated by different abilities to recruit SMRT/N-Cor transcriptional complex. Their target genes are predominantly spermatid-specific multicopy genes encoded by the sex chromosomes and the autosomal Speer/Takusan. Many of them have coamplified with not only Slx/Slxl1/Sly but also Ssty during muroid rodent evolution. Overall, we identify Ssty as a key element of the X versus Y intragenomic conflict, which may have influenced gene content and hybrid sterility beyond Mus lineage since Ssty amplification on the Y predated that of Slx/Slxl1/Sly.

Males can adjust offspring sex ratio in an adaptive fashion through different mechanisms

Sex allocation research has primarily focused on offspring sex-ratio adjustment by mothers. Yet, fathers also benefit from producing more of the sex with greater fitness returns. Here, we review the state-of-the art in the study of male-driven sex allocation and, counter to the current paradigm, we propose that males can adaptively influence offspring sex ratio through a wide variety of mechanisms. This includes differential production and motility of X- versus Y-bearing sperms in mammals, variation in seminal fluid composition in haplo-diploid invertebrates, and epigenetic mechanisms in some fish and lizards exhibiting environmental sex determination. Conflicts of interest between mothers and fathers over offspring sex ratios can emerge, although many more studies are needed in this area. While many studies of sex allocation have focused on adaptive explanations with little attention to mechanisms, and vice versa, the integration of these two topics is essential for understanding male-driven sex allocation.

Mechanisms of meiotic drive in symmetric and asymmetric meiosis

Meiotic drive, the non-Mendelian transmission of chromosomes to the next generation, functions in asymmetric or symmetric meiosis across unicellular and multicellular organisms. In asymmetric meiosis, meiotic drivers act to alter a chromosome's spatial position in a single egg. In symmetric meiosis, meiotic drivers cause phenotypic differences between gametes with and without the driver. Here we discuss existing models of meiotic drive, highlighting the underlying mechanisms and regulation governing systems for which the most is known. We focus on outstanding questions surrounding these examples and speculate on how new meiotic drive systems evolve and how to detect them.

The micro-RNA content of unsorted cryopreserved bovine sperm and its relation to the fertility of sperm after sex-sorting

BACKGROUND

The use of sex-sorted sperm in cattle assisted reproduction is constantly increasing. However, sperm fertility can substantially differ between unsorted (conventional) and sex-sorted semen batches of the same sire. Sperm microRNAs (miRNA) have been suggested as promising biomarkers of bull fertility the last years. In this study, we hypothesized that the miRNA profile of cryopreserved conventional sperm is related to bull fertility after artificial insemination with X-bearing sperm. For this purpose, we analyzed the miRNA profile of 18 conventional sperm samples obtained from nine high- (HF) and nine low-fertility (LF) bulls that were contemporaneously used to produce conventional and sex-sorted semen batches. The annual 56-day non-return rate for each semen type (NRRconv and NRRss, respectively) was recorded for each bull.

RESULTS

In total, 85 miRNAs were detected. MiR-34b-3p and miR-100-5p were the two most highly expressed miRNAs with their relative abundance reaching 30% in total. MiR-10a-5p and miR-9-5p were differentially expressed in LF and HF samples (false discovery rate < 10%). The expression levels of miR-9-5p, miR-34c, miR-423-5p, miR-449a, miR-5193-5p, miR-1246, miR-2483-5p, miR-92a, miR-21-5p were significantly correlated to NRRss but not to NRRconv. Based on robust regression analysis, miR-34c, miR-7859 and miR-342 showed the highest contribution to the prediction of NRRss.

CONCLUSIONS

A set of miRNAs detected in conventionally produced semen batches were linked to the fertilizing potential of bovine sperm after sex-sorting. These miRNAs should be further evaluated as potential biomarkers of a sire's suitability for the production of sex-sorted sperm.

The Theory and Applications of Measuring Broad-Range and Chromosome-Wide Recombination Rate from Allele Frequency Decay around a Selected Locus

Recombination is the exchange of genetic material between homologous chromosomes via physical crossovers. High-throughput sequencing approaches detect crossovers genome wide to produce recombination rate maps but are difficult to scale as they require large numbers of recombinants individually sequenced. We present a simple and scalable pooled-sequencing approach to experimentally infer near chromosome-wide recombination rates by taking advantage of non-Mendelian allele frequency generated from a fitness differential at a locus under selection. As more crossovers decouple the selected locus from distal loci, the distorted allele frequency attenuates distally toward Mendelian and can be used to estimate the genetic distance. Here, we use marker selection to generate distorted allele frequency and theoretically derive the mathematical relationships between allele frequency attenuation, genetic distance, and recombination rate in marker-selected pools. We implemented nonlinear curve-fitting methods that robustly estimate the allele frequency decay from batch sequencing of pooled individuals and derive chromosome-wide genetic distance and recombination rates. Empirically, we show that marker-selected pools closely recapitulate genetic distances inferred from scoring recombinants. Using this method, we generated novel recombination rate maps of three wild-derived strains of Drosophila melanogaster, which strongly correlate with previous measurements. Moreover, we show that this approach can be extended to estimate chromosome-wide crossover interference with reciprocal marker selection and discuss how it can be applied in the absence of visible markers. Altogether, we find that our method is a simple and cost-effective approach to generate chromosome-wide recombination rate maps requiring only one or two libraries.

Suppression of Non-Random Fertilization by MHC Class I Antigens

Hermaphroditic invertebrates and plants have a self-recognition system on the cell surface of sperm and eggs, which prevents their self-fusion and enhances non-self-fusion, thereby contributing to genetic variation. However, the system of sperm-egg recognition in mammals is under debate. To address this issue, we explored the role of major histocompatibility complex class I (MHC class I, also known as histocompatibility 2-Kb or H2-Kb and H2-Db in mice) antigens by analyzing H2-Kb-/-H2-Db-/-β2-microglobulin (β2M)-/- triple-knockout (T-KO) male mice with full fertility. T-KO sperm exhibited an increased sperm number in the perivitelline space of wild-type (WT) eggs in vitro. Moreover, T-KO sperm showed multiple fusion with zona pellucida (ZP)-free WT eggs, implying that the ability of polyspermy block for sperm from T-KO males was weakened in WT eggs. When T-KO male mice were intercrossed with WT female mice, the percentage of females in progeny increased. We speculate that WT eggs prefer fusion with T-KO sperm, more specifically X-chromosome-bearing sperm (X sperm), suggesting the presence of preferential (non-random) fertilization in mammals, including humans.

Itaconate regulates the glycolysis/pentose phosphate pathway transition to maintain boar sperm linear motility by regulating redox homeostasis

Mammalian cells improve redox homeostasis under reactive oxygen species (ROS) stress conditions via the enhancement of the pentose phosphate pathway (PPP). However, it is not clear how the cell reprograms glucose metabolism from glycolysis to the PPP. Hence, in the present study, we used boar sperm as a model to elucidate the mechanism by which the glycolysis/PPP transition occurs under ROS stress. The boar sperm treated with moderate glucose levels for 3 h exhibited increased sperm linear motility patterns, ATP levels and GSH/GSSG ratios and decreased ROS levels compared to the boar sperm treated without glucose. In addition, the hexokinase activity, glucose-6-phosphate dehydrogenase (G6PD) activity, NADPH level, NADPH/NADP⁺ ratio and mitochondrial activity were higher in the sperm treated with moderate glucose than in those not treated with glucose. Interestingly, the enzyme activity of fructose-1,6-bisphosphate aldolase (ALDOA) was not significantly changed during the incubation. The sperm linear motility patterns were decreased by treatment with the G6PD inhibitor 6-aminonicotinamide. Moreover, moderate glucose treatment significantly increased the itaconate levels in sperm. Both endogenous and exogenous itaconate increased the total itaconate modifications and the itaconate-modified ALDOA levels in sperm, suggesting that under moderate-glucose conditions, glycolysis in the sperm was suppressed by an increase in the itaconate levels. Furthermore, the addition of itaconate improved the sperm linear motility patterns by suppressing glycolysis and enhancing oxidative phosphorylation (OXPHOS). Therefore, the itaconate generated from OXPHOS regulates the glycolysis/PPP transition to maintain redox homeostasis. In sperm, this itaconate-dependent mechanism plays an important role in maintaining their high linear motility.

Within-ejaculate sperm competition

Sperm competition was defined by Geoff Parker 50 years ago as the competition between sperm from two or more males over the fertilization of a set of eggs. Since the publication of his seminal paper, sperm competition has developed into a large field of research, and many aspects are still being discovered. One of the relatively poorly understood aspects is the importance of selection and competition among sperm within the ejaculate of a male. The sheer number of sperm present in a male's ejaculate suggests that the competition among sibling sperm produced by the same male may be intense. In this review, we summarize Parker's theoretical models generating predictions about the evolution of sperm traits under the control of the haploid gamete as opposed to the diploid male. We review the existing evidence of within-ejaculate competition from a wide range of fields and taxa. We also discuss the conceptual and practical hurdles we have been facing to study within-ejaculate sperm competition, and how novel technologies may help in addressing some of the currently open questions.

This article is part of the theme issue ‘Fifty years of sperm competition’.

Targeting of the Dosage-Compensated Male X-Chromosome during Early Drosophila Development

Dosage compensation, which corrects for the imbalance in X-linked gene expression between XX females and XY males, represents a model for how genes are targeted for coordinated regulation. However, the mechanism by which dosage compensation complexes identify the X chromosome during early development remains unknown because of the difficulty of sexing embryos before zygotic transcription using X- or Y-linked reporter transgenes. We used meiotic drive to sex Drosophila embryos before zygotic transcription and ChIP-seq to measure the dynamics of dosage compensation factor targeting. The Drosophila male-specific lethal dosage compensation complex (MSLc) requires the ubiquitous zinc-finger protein chromatin-linked adaptor for MSL proteins (CLAMP) to identify the X chromosome. We observe a multi-stage process in which MSLc first identifies CLAMP binding sites throughout the genome, followed by concentration at the strongest X-linked MSLc sites. We provide insight into the dynamics of binding site recognition by a large transcription complex during early development.

Rieder et al. establish a meiotic drive system to study Drosophila X chromosome dosage compensation before the maternal-zygotic transition. This study uncovers another step in the process during which the dosage compensation complex identifies binding sites genome-wide before becoming enriched on the X chromosome.

Toll-Like Receptors Contribute to Sex Differences in Blood Pressure Regulation

Toll-like receptors (TLRs) play an important role in the innate immune system, and recently, they have been shown to be involved in the regulation of blood pressure. The incidence of hypertension is higher in men, and it increases in postmenopausal women. In fact, premenopausal women are protected from cardiovascular disease compared with age-matched men, and it is well established that this protective effect is lost with menopause. However, the molecular mechanisms underlying this protection in women are unknown. Whether or not it could be related to differential activation of the innate immune system remains to be elucidated. This review focuses on (1) the differences between men and women in TLR activation and (2) whether TLR activation may influence the regulation of blood pressure in a sex-dependent manner.

Sex Manipulation Technologies Progress in Livestock: A Review

Sex manipulation technologies allow predetermination of the sex of animal offspring by altering the normal reproductive process. In livestock production, the difference in type and gender can translate into significant economic benefits, including alleviation of severe food shortages. In livestock, however, the commercial application of sex manipulation technologies is currently available for cattle only. In this review, we described the brief history of sex manipulation, and the research progresses of common methods used in sex manipulation thus far. Information presented in this review can inform future studies on expanding the scope and use of sex manipulation technologies in livestock.

Advances and challenges in genetic technologies to produce single-sex litters

There is currently a requirement for single-sex litters for many applications, including agriculture, pest control, and reducing animal culling in line with the 3Rs principles: Reduction, Replacement, and Refinement. The advent of CRISPR/Cas9 genome editing presents a new opportunity with which to potentially generate all-female or all-male litters. We review some of the historical nongenetic strategies employed to generate single-sex litters and investigate how genetic and genome editing techniques are currently being used to produce all-male or all-female progeny. Lastly, we speculate on future technologies for generating single-sex litters and the possible associated challenges.

Sperm sex ratio adjustment in a mammal: perceived male competition leads to elevated proportions of female-producing sperm

Mammal sex allocation research has focused almost exclusively on maternal traits, but it is now apparent that fathers can also influence offspring sex ratios. Parents that produce female offspring under conditions of intense male-male competition can benefit with greater assurance of maximized grand-parentage. Adaptive adjustment in the sperm sex ratio, for example with an increase in the production of X-chromosome bearing sperm (CBS), is one potential paternal mechanism for achieving female-biased sex ratios. Here, we tested this mechanistic hypothesis by varying the risk of male-male competition that male house mice perceived during development, and quantifying sperm sex ratios at sexual maturity. Our analyses revealed that males exposed to a competitive 'risk' produced lower proportions of Y-CBS compared to males that matured under 'no risk' of competition. We also explored whether testosterone production was linked to sperm sex ratio variation, but found no evidence to support this. We discuss our findings in relation to the adaptive value of sperm sex ratio adjustments and the role of steroid hormones in socially induced sex allocation.

Successful selection of mouse sperm with high viability and fertility using microfluidics chip cell sorter

Cell sorting via flow cytometry is a powerful tool to select subpopulations of cells in many biological fields. Selection of fertilisation-prone sperm is a critical step to ensure a stable and high fertilisation rate in in vitro fertilisation (IVF). However, a combination of conventional cell sorting and IVF system has not been established because of severe mechanical damages to the sperm during the sorting process. A cell sorter with microfluidics chip technology that lessens cell damage during cell sorting may address this problem. We evaluated the effects of microfluidics chip cell sorting on the sperm using the parameters, such as motility and fertility, and found this cell sorting method had minimal harmful effect on the sperm. Then, sperm were selected by a marker for acrosome reaction and showed higher fertilisation rate than that of the population of acrosome-intact sperm. Embryo derived from these sperm developed normally. These results indicated that microfluidics chip cell sorting can select fertile sperm to improve IVF technique.

Social Media Sensationalism in the Male Infertility Space: A Mixed Methodology Analysis

Purpose

Infertile couples increasingly turn to the internet for medical guidance. The aims of this study were: (1) to identify popular male infertility content on social media, and (2) to assess the accuracy and quality of this content. We hypothesized that inaccurate/misleading information proliferates online.

Materials and Methods

We used the analytics module BuzzSumo to identify article links that were most shared on Facebook, Pinterest, Reddit, and Twitter related to male infertility during September 2018 to August 2019. We excluded articles with <100 engagements, defined as “likes,” “comments,” and “shares.” Two researchers graded content as accurate, misleading, or inaccurate by comparing content to references cited and contemporary research. Inter-rater reliability was determined with Cohen's κ. Binary logistic regression was performed to compare user engagement with accurate versus inaccurate/misleading articles.

Results

Fifty-two unique article links were identified, with 421,004 total engagements. Thirty-four articles referenced 15 scientific studies; no reference was available for 18 links. Fifty-six percent of articles were accurate and 44% misleading/inaccurate (κ=0.743). No significant difference was found in total engagement between accurate vs. misleading/inaccurate links (p=0.805). Twenty-four percent of engagements referenced studies using non-human models, and 26% of studies had sample sizes <100.

Conclusions

Social media platforms foster engagement with male infertility information. However, sensationalism predominates, as patients are highly likely to encounter misleading/inaccurate information, articles that overstate implications of animal research, and conclusions made based on limited sample sizes. Urologists should consider adding social media to their armamentarium to stave off misinformation and engage proactively with patients.

Sex and suicide: The curious case of Toll-like receptors

During in vitro fertilisation (IVF), pharmacological activation of the murine X chromosome-encoded receptor proteins Toll-like receptor (TLR) 7 and TLR8 reportedly results in male-biased litters by selectively disrupting the motility of X-bearing sperm cells. Thus-in the context of agonist treatment during IVF-these receptors act as 'suicidal' segregation distorters that impair their own transmission to the next generation. Such behaviour would, from an evolutionary perspective, be strongly selected against if present during natural fertilisation. Consequently, TLR7/8 biology in vivo must differ significantly from this in vitro situation to allow these genes to persist in the genome. Here, we use our current understanding of male germ cell biology and TLR function as a starting point to explore the mechanistic and evolutionary aspects of this apparent paradox.

A phenotypic screening platform utilising human spermatozoa identifies compounds with contraceptive activity

There is an urgent need to develop new methods for male contraception, however a major barrier to drug discovery has been the lack of validated targets and the absence of an effective high-throughput phenotypic screening system. To address this deficit, we developed a fully-automated robotic screening platform that provided quantitative evaluation of compound activity against two key attributes of human sperm function: motility and acrosome reaction. In order to accelerate contraceptive development, we screened the comprehensive collection of 12,000 molecules that make up the ReFRAME repurposing library, comprising nearly all the small molecules that have been approved or have undergone clinical development, or have significant preclinical profiling. We identified several compounds that potently inhibit motility representing either novel drug candidates or routes to target identification. This platform will now allow for major drug discovery programmes that address the critical gap in the contraceptive portfolio as well as uncover novel human sperm biology.

New Biological Insights on X and Y Chromosome-Bearing Spermatozoa

A spermatozoon is a male germ cell capable of fertilizing an oocyte and carries genetic information for determining the sex of the offspring. It comprises autosomes and an X (X spermatozoa) or a Y chromosome (Y spermatozoa). The origin and maturation of both X and Y spermatozoa are the same, however, certain differences may exist. Previous studies proposed a substantial difference between X and Y spermatozoa, however, recent studies suggest negligible or no differences between these spermatozoa with respect to ratio, shape and size, motility and swimming pattern, strength, electric charge, pH, stress response, and aneuploidy. The only difference between X and Y spermatozoa lies in their DNA content. Moreover, recent proteomic and genomic studies have identified a set of proteins and genes that are differentially expressed between X and Y spermatozoa. Therefore, the difference in DNA content might be responsible for the differential expression of certain genes and proteins between these cells. In this review, we have compiled our present knowledge to compare X and Y spermatozoa with respect to their structural, functional, and molecular features. In addition, we have highlighted several areas that could be explored in future studies in this field.