Sperm-egg Recognition Research Articles

ROLE OF INTEGRINS IN HUMAN SPERM CELLS ON THE REPRODUCTION PROCESS

Ovum and spermatozoa cells, namely male and female reproductive cells that unite at the time of fertilization, are synchronized molecular events that occur sequentially. Apart from being present in the egg cell, adhesion molecules called integrins are also involved in this molecular process. However, recently, these integrins have also been found in spermatozoa cells, especially in the head and tail areas. Because this problem is intended as an introduction to the laboratory which is part of the thesis research, the method used in this research is a literature review whose publication age is not more than 10 years. Research findings indicate that integrins play a crucial role in egg-sperm recognition, their interaction, and fusion, potentially addressing infertility issues in couples of reproductive age.

Lectin-Based SP3 Technology Enables N-Glycoproteomic Analysis of Mouse Oocytes.

N-glycosylation is one of the most universal and complex protein post-translational modifications (PTMs), and it is involved in many physiological and pathological activities. Owing to the low abundance of N-glycoproteins, enrichment of N-glycopeptides for mass spectrometry analysis usually requires a large amount of peptides. Additionally, oocyte protein N-glycosylation has not been systemically characterized due to the limited sample amount. Here, we developed a glycosylation enrichment method based on lectin and a single-pot, solid-phase-enhanced sample preparation (SP3) technology, termed lectin-based SP3 technology (LectinSP3). LectinSP3 immobilized lectin on the SP3 beads for N-glycopeptide enrichment. It could identify over 1100 N-glycosylation sites and 600 N-glycoproteins from 10 μg of mouse testis peptides. Furthermore, using the LectinSP3 method, we characterized the N-glycoproteome of 1000 mouse oocytes in three replicates and identified a total of 363 N-glycosylation sites from 215 N-glycoproteins. Bioinformatics analysis revealed that these oocyte N-glycoproteins were mainly enriched in cell adhesion, fertilization, and sperm-egg recognition. Overall, the LectinSP3 method has all procedures performed in one tube, using magnetic beads. It is suitable for analysis of a low amount of samples and is expected to be easily adaptable for automation. In addition, our mouse oocyte protein N-glycosylation profiling could help further characterize the regulation of oocyte functions.

Inceptor facilitates acrosomal vesicle formation in spermatids and is required for male fertility.

Spermatogenesis is a crucial biological process that enables the production of functional sperm, allowing for successful reproduction. Proper germ cell differentiation and maturation require tight regulation of hormonal signals, cellular signaling pathways, and cell biological processes. The acrosome is a lysosome-related organelle at the anterior of the sperm head that contains enzymes and receptors essential for egg-sperm recognition and fusion. Even though several factors crucial for acrosome biogenesis have been discovered, the precise molecular mechanism of pro-acrosomal vesicle formation and fusion is not yet known. In this study, we investigated the role of the insulin inhibitory receptor (inceptor) in acrosome formation. Inceptor is a single-pass transmembrane protein with similarities to mannose-6-phosphate receptors (M6PR). Inceptor knockout male mice are infertile due to malformations in the acrosome and defects in the nuclear shape of spermatozoa. We show that inceptor is expressed in early spermatids and mainly localizes to vesicles between the Golgi apparatus and acrosome. Here we show that inceptor is an essential factor in the intracellular transport of trans-Golgi network-derived vesicles which deliver acrosomal cargo in maturing spermatids. The absence of inceptor results in vesicle-fusion defects, acrosomal malformation, and male infertility. These findings support our hypothesis of inceptor as a universal lysosomal or lysosome-related organelle sorting receptor expressed in several secretory tissues.

Establishment of a repertoire of fertility associated sperm proteins and their differential abundance in buffalo bulls (Bubalus bubalis) with contrasting fertility

Sperm harbours a wide range of proteins regulating their functions and fertility. In the present study, we made an effort to characterize and quantify the proteome of buffalo bull spermatozoa, and to identify fertility associated sperm proteins through comparative proteomics. Using high-throughput mass spectrometry platform, we identified 1305 proteins from buffalo spermatozoa and found that these proteins were mostly enriched in glycolytic process, mitochondrial respiratory chain, tricarboxylic acid cycle, protein folding, spermatogenesis, sperm motility and sperm binding to zona pellucida (p < 7.74E−08) besides metabolic (p = 4.42E−31) and reactive oxygen species (p = 1.81E−30) pathways. Differential proteomic analysis revealed that 844 proteins were commonly expressed in spermatozoa from both the groups while 77 and 52 proteins were exclusively expressed in high- and low-fertile bulls, respectively. In low-fertile bulls, 75 proteins were significantly (p < 0.05) upregulated and 176 proteins were significantly (p < 0.05) downregulated; these proteins were highly enriched in mitochondrial respiratory chain complex I assembly (p = 2.63E−07) and flagellated sperm motility (p = 7.02E−05) processes besides oxidative phosphorylation pathway (p = 6.61E−15). The down regulated proteins in low-fertile bulls were involved in sperm motility, metabolism, sperm-egg recognition and fertilization. These variations in the sperm proteome could be used as potential markers for the selection of buffalo bulls for fertility.

Comparative proteomic analysis of seminal plasma exosomes in buffalo with high and low sperm motility

BackgroundExosomes are nanosized membranous vesicles secreted by various types of cells, which facilitate intercellular communication by transporting bioactive compounds. Exosomes are abundant in biological fluids including semen, and their protein composition and the potential of seminal plasma exosomes (SPEs) as fertility biomarkers were elucidated in humans, however, little information is available regarding buffalo (Bubalus bubalis). Here, we examined protein correlation between spermatozoa, seminal plasma (SP), and SPEs, and we compared and analyzed protein differences between high-motility (H-motility) and low-motility (L-motility) SPEs in buffalo.ResultsSPEs were concentrated and purified by ultracentrifugation combined with sucrose density gradient centrifugation, followed by verification using western blotting, nanoparticle tracking analysis, and transmission electron microscopy. Protein composition in spermatozoa, SP and SPEs, and protein difference in H- and L-motility SPEs were identified by LC-MS/MS proteomic analysis and were functionally analyzed through comprehensive bioinformatics. Many SPEs proteins originated from spermatozoa and SP, and nearly one third were also present in spermatozoa and SP. A series of proteins associated with reproductive processes including sperm capacitation, spermatid differentiation, fertilization, sperm-egg recognition, membrane fusion, and acrosome reaction were integrated in a functional network. Comparative proteomic analyses showed 119 down-regulated and 41 up-regulated proteins in L-motility SPEs, compared with H-motility SPEs. Gene Ontology (GO) enrichment of differentially expressed proteins (DEPs) showed that most differential proteins were located in sperm and vesicles, with activities of hydrolase and metalloproteinase, and were involved in sperm-egg recognition, fertilization, single fertilization, and sperm-zona pellucida binding processes, etc. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that differential proteins were mainly involved in the PPRP signaling pathway, calcium signaling pathway, and cAMP signaling pathway, among others. Furthermore, 6 proteins associated with reproduction were validated by parallel reaction monitoring analysis.ConclusionThis study provides a comprehensive description of the seminal plasma exosome proteome and may be of use for further screening of biomarkers associated with male infertility.

Triploidization of rainbow trout affects proteins related to ovary development and reproductive activity

Rainbow trout are characterized by high amenability to chromosome manipulations during early development to produce androgens, gynogens, or sterile triploids, which are relevant in aquaculture. An understanding of the mechanisms affecting oogenesis and those resulting in diminished gonadal development in triploids is an important area of scientific study. Therefore, the aim of this study was to compare the ovary proteome from triploid (3 N) and diploid (2 N) rainbow trout females using tandem mass tag (TMT) peptide labelling coupled with liquid chromatography–mass spectrometry (LC–MS/MS) to identify differentially expressed proteins (DEPs) between 2 N and 3 N. The potential biological role of DEPs was also explored using comparative functional gene set enrichment to designate the potential protein markers of 3 N sterility. We identified a total of 3899 DEPs (q < 0.05), including 956 downregulated and 2943 upregulated proteins in 3 N ovaries compared to 2 N ovaries. The identified clusters for downregulated proteins in 3 N included lipid metabolic process, hormone biosynthesis, transport and exocytosis, cell junction organization and sperm-egg recognition, which can result in (i) the disruption of lipid, steroid hormone and vitellogenesis processes, (ii) impaired amino acid uptake, (iii) defects in cell–cell junctions reflecting tissue abnormalities and aberrant gonadal morphology, and (iv) impaired functions related to maintaining the proper structure of the vitelline envelope, oocyte formation and fertilization competence. With respect to upregulated proteins in 3 N ovaries, RNA processing, cell cycle, cytoskeleton organization and regulation of metabolic process were the primary clusters, which may reflect (i) the disturbance to RNA processing responsible for impairment of ovary development in triploid rainbow trout, (ii) disruption of spindle formation, incorrect chromosome alignment and segregation during meiotic division, (iii) increase in regulatory mechanism of apoptosis, which in consequence can provoke abnormal gonadal development and sterility, and (iv) enhanced ubiquitin–proteasome system governing aberrant gonadal morphology in 3 N females and oocyte maturation. The obtained results provide an accurate portrait of molecular changes in rainbow trout ovaries in response to triploidization and may contribute to a better understanding of the mechanisms responsible for impaired oogenesis in rainbow trout triploid females, which in turn leads to their sterility. Data are available via ProteomeXchange with identifier PXD034492.

Comparison of Fecundity Traits between Mauremys reevesii and Trachemys scripta based on Gene Family Analysis

Background: Chinese pond turtle (CPT, Mauremys reevesii) is a typical species with temperature-dependent sex determination (TSD). Pond slider turtle (PST, Trachemys scripta) is considered one of the worst invasive species in the world. In order to analyze the adaptive evolution of fecundity traits in CPT and TSD, the rapidly evolving gene families were obtained and functional enrichment analysis was performed. At the same time, CPT and PST species-specific genes were also enriched for their fecundity traits. Methods: Orthofinder software was employed to search homologous genes based on protein sequence. CAFÉ software was used to obtain the expansion and contraction gene families of CPT and PST. Then, GO terms and pathway enrichment analyses were performed using TBtools software and Swissprot database. Result: In CPT, 159 rapid expansion gene families GO enrichment results showed that the reproductive activities related pathways were mainly three significant enrichment process, spermatogenesis, steroid hormone mediated signaling pathway and male gamete generation. 2 rapidly contraction gene families showed that there was no significant enrichment pathway related to reproduction. The pathway of significant enrichment were RNA biosynthetic process, regulation of RNA metabolic process and regulation of cellular metabolic process. The gene families unique to the species were significantly enriched in pathways DNA replication-dependent nucleosome organization, DNA replication-dependent nucleosome assembly and negative regulation of megakaryocyte differentiation. In PST, 15 rapid expansion gene families GO enrichment results showed that the most significant GO terms mainly consisted of biological processes which were involved in endocrine process, regulation of endocrine process and cellular response to steroid hormone stimulus, but spermatogenesis and male gamete generation gene families also expanded. 58 rapidly contraction gene families showed that the pathways of significant enrichment were endocrine process, cellular response to steroid hormone stimulus and regulation of endocrine process. At the same time, estrogen secretion, binding of sperm to zona pellucida and sperm-egg recognition gene family also rapidly contraction. The gene families unique to the species were significantly enriched in pathways adenylate cyclase-activating G protein-coupled receptor signaling pathway, double-strand break repair and regulation of potassium ion transport.

Implications of sperm heat shock protein 70-2 in bull fertility

Heat shock protein 70 (HSP70) is one of the most abundant chaperone proteins. Their function is well documented in facilitating the protein synthesis, translocation, de novo folding, and ordering of multiprotein complexes. HSP70 in bovine consists of four genes: HSP70-1, HSP70-2, HSP70-3, and HSP70-4. HSP70-2 was found to be involved in fertility. Current knowledge implicates HSP70-2 in sperm quality, sperm capacitation, sperm–egg recognition, and fertilization essential for bull reproduction. HSP70-2 is also involved in the biological processes of spermatogenesis, as it protects cells from the effects of apoptosis and oxidative stress. Fertilization success is not only determined by the amount of sperm found in the female reproductive tract but also by the functional ability of the sperm. However, subfertility is more likely to be associated with changes in sperm molecular dynamics not detectable using conventional methods. As such, molecular analyses and omics methods have been developed to monitor crucial aspects of sperm molecular morphology that are important for sperm functions, which are the objectives of this review.

PRSS37 deficiency leads to impaired energy metabolism in testis and sperm revealed by DIA-based quantitative proteomic analysis.

Our previous studies have reported that a putative trypsin-like serine protease, PRSS37, is exclusively expressed in testicular germ cells during late spermatogenesis and essential for sperm migration from the uterus into the oviduct and sperm-egg recognition via mediating the interaction between PDILT and ADAM3. In the present study, the global proteome profiles of wild-type (wt) and Prss37-/- mice in testis and sperm were compared employing data independent acquisition (DIA) technology. Overall, 2506 and 459 differentially expressed proteins (DEPs) were identified in Prss37-null testis and sperm, respectively, when compared to control groups. Bioinformatic analyses revealed that most of DEPs were related to energy metabolism. Of note, the DEPs associated with pathways for the catabolism such as glucose via glycolysis, fatty acids via β-oxidation, and amino acids via oxidative deamination were significantly down-regulated. Meanwhile, the DEPs involved in the tricarboxylic acid cycle (TCA cycle) and oxidative phosphorylation (OXPHOS) were remarkably decreased. The DIA data were further confirmed by a markedly reduction of intermediate metabolites (citrate and fumarate) in TCA cycle and terminal metabolite (ATP) in OXPHOS system after disruption of PRSS37. These outcomes not only provide a more comprehensive understanding of the male fertility of energy metabolism modulated by PRSS37 but also furnish a dynamic proteomic resource for further reproductive biology studies.

Cysteine is highly enriched in the canonical N-linked glycosylation motif of bovine spermatozoa N-Glycoproteome

Glycosylation, one of the most important post-translational modifications of proteins, plays an irreplaceable role in the whole process of spermatogenesis, sperm-egg recognition, and fertilization. Herein, we mapped the first bovine sperm N-linked glycoproteome and a total of 1188 N-glycosylated sites on 626 proteins were identified. Bioinformatics analysis revealed that bovine sperm N-glycosylated proteins were classified into “extracellular region” and “lysosome” groups based on cellular component annotation and enrichment of glycoproteins with proteolytic and reproductive functions. Notably, cysteines were highly enriched in the canonical N-glycosylation motifs N-!P-[S/T/C] and the conservative motifs N–C-[S/T] were also significantly enriched, indicating these modifications play extraordinary roles in bovine spermatogenesis and maturation. The percentage of cysteine at the second position relative to modified asparagine was 7.5%, much higher than that of the previously reported N-linked glycoproteome. A total of 120 cysteine enriched N-glycoproteins were identified, which had significantly upregulated metalloendopeptidase activity and metal ion binding compared with the whole bovine sperm glycoproteome. Strikingly, 15 of 58 N–C-[S/T] motif-containing glycoproteins had a disintegrin and metalloproteinase (ADAM) protein domain. Thus, we hypothesized that ADAM-containing conserved free cysteine residues in N-linked glycoprotein motifs may be key cysteine-switches and may have extraordinary roles in bovine spermatozoa. In conclusion, almost all bovine sperm glycoproteins have enzyme activity, participate in proteolysis, and play indispensable roles in spermatogenesis, sperm-egg recognition, and eventual fertilization. The mapping of N-glycosylation on bovine sperm may provide a new means to explore potential biomarkers for improving sperm quality and fertility.

Precision Glycoproteomics Reveals Distinctive N-Glycosylation in Human Spermatozoa

Spermatozoon represents a very special cell type in human body, and glycosylation plays essential roles in its whole life including spermatogenesis, maturation, capacitation, sperm–egg recognition, and fertilization. In this study, by mapping the most comprehensive N-glycoproteome of human spermatozoa using our recently developed site-specific glycoproteomic approaches, we show that spermatozoa contain a number of distinctive glycoproteins, which are mainly involved in spermatogenesis, acrosome reaction and sperm:oocyte membrane binding, and fertilization. Heavy fucosylation is observed on 14 glycoproteins mostly located at extracellular and cell surface regions in spermatozoa but not in other tissues. Sialylation and Lewis epitopes are enriched in the biological process of immune response in spermatozoa, while bisected core structures and LacdiNAc structures are highly expressed in acrosome. These data deepen our knowledge about glycosylation in spermatozoa and lay the foundation for functional study of glycosylation and glycan structures in male infertility.

Polarized epithelium-sperm co-culture system reveals stimulatory factors for the secretion of mouse epididymal quiescin sulfhydryl oxidase 1.

Spermatozoa acquire fertilization ability through post-translational modifications. These membrane surface alterations occur in various segments of the epididymis. Quiescin sulfhydryl oxidases, which catalyze thiol-oxidation reactions, are involved in disulfide bond formation, which is essential for sperm maturation, upon transition and migration in the epididymis. Using castration and azoospermia transgenic mouse models, in the present study, we showed that quiescin sulfhydryl oxidase 1 (QSOX1) protein expression and secretion are positively correlated with the presence of testosterone and sperm cells. A two-dimensional in vitro epithelium-sperm co-culture system provided further evidence in support of the notion that both testosterone and its dominant metabolite, 5α-dihydrotestosterone, promote epididymal QSOX1 secretion. We also demonstrated that immature caput spermatozoa, but not mature cauda sperm cells, exhibited great potential to stimulate QSOX1 secretion in vitro, suggesting that sperm maturation is a key regulatory factor for mouse epididymal QSOX1 secretion. Proteomic analysis identified 582 secretory proteins from the co-culture supernatant, of which 258 were sperm-specific and 154 were of epididymal epithelium-origin. Gene Ontology analysis indicated that these secreted proteins exhibit functions known to facilitate sperm membrane organization, cellular activity, and sperm-egg recognition. Taken together, our data demonstrated that testosterone and sperm maturation status are key regulators of mouse epididymal QSOX1 protein expression and secretion.

Surgical face masks as a source of emergent pollutants in aquatic systems: Analysis of their degradation product effects in Danio rerio through RNA-Seq.

Surgical face masks are the most popularised and effective personal equipment for protecting public health during the COVID-19 pandemic. They are composed of plastic polymer fibres with a large amount of inorganic and organic compounds that can be released into aquatic environments through degradation processes. This source of microplastics and inorganic and organic substances could potentially impact aquatic organisms. In this study, the toxicogenomic effects of face masks at different stages of degradation in water were analysed in zebrafish larvae (Danio rerio) through RNA-Seq. Larvae were exposed for 10 days to three treatments: 1) face mask fragments in an initial stage of degradation (poorly degraded masks -PDM- products) with the corresponding water; 2) face mask fragments in an advanced stage of degradation (highly degraded masks -HDM- products) with the corresponding water; and 3) water derived from HDM (W-HDM). Transcriptome analyses revealed that the three treatments provoked the down-regulation of genes related to reproduction, especially the HDM products, suggesting that degradation products derived from face masks could act as endocrine disruptors. The affected genes are involved in different steps of reproduction, including gametogenesis, sperm-egg recognition and binding or fertilisation. Immune-related genes and metabolic processes were also differentially affected by the treatments.

The interaction between Tu-Izumo1 and Tu-JUNO is involved in turtles hybridization.

The specificity of sperm-egg recognition is crucial to species independence, and two proteins (Izumo1 and JUNO) are essential for gamete adhesion/fusion in mammals. However, hybridization, which is very common in turtles, also requires specific recognition of sperm-egg binding proteins. In this study, we discovered that natural selection plays an important role in the codon usage bias of Tu-Izumo1 and Tu-JUNO. Positively selected sites and co-evolutionary analyses between Tu-Izumo1 and Tu-JUNO have been previously reported, and we confirm these results in a larger analysis containing 25 turtle species. We also showed that Tu-JUNO is expressed on the oocyte surface and that Tu-Izumo1 and Tu-JUNO interact with each other directly in different species hybridization combinations. Co-immunization assays revealed that this interaction is evolutionarily conserved in turtles. The results of avidity-based extracellular interaction screening between Tu-Izumo1 and Tu-JUNO for sperm-oocyte binding pairs (both within and across species) likely suggest that the interaction force between Izumo1 and JUNO has a certain correlation in whether the turtles can hybridize. Our results lay a theoretical foundation for the subsequent development of techniques to detect whether different turtle species can interbreed, which would provide the molecular basis for breeding management and species protection of turtles.

Aquaculture potential of two Kumamoto oyster (Crassostrea sikamea) populations and their reciprocal hybrids in southern China

The Kumamoto oyster, Crassostrea sikamea, is a potential aquaculture species with a unique shape and delicious taste. It is naturally distributed along the coasts of East Asia, but it was inadvertently introduced into America from Japan, and has formed several geographic populations. In order to evaluate the aquaculture potential of C. sikamea hybrids, a complete diallel cross between two geographical populations (China and America) was conducted by using mixing gametes at an experimental station in Zhanjiang, Guangdong Province in southern China. Two intra-population mating groups (CC and AA) and two reciprocal inter-population crosses (CA and AC) were produced in triplicates. High fertilization rate and hatching rate were observed in all experimental groups, suggesting that there was no sperm-egg recognition barrier between these two geographic populations. Throughout the life cycle, the survival rate of reciprocal hybrids was higher than that of pure breeds. The heterosis in growth of whole weight of reciprocal hybrids in adulthood was significant, which was mainly influenced by mating strategy. In view of the performance difference between the progenies of the two pure populations, the aquaculture potential of the progenies of the American C. sikamea population was higher than that of the progenies of the Chinese indigenous population. The results demonstrated that the crossbreeding between Chinese and American C. sikamea populations can produce considerable heterosis, which can improve the C. sikamea aquaculture industry in southern China.

Comparative Proteomics and Phosphoproteomics Analysis Reveal the Possible Breed Difference in Yorkshire and Duroc Boar Spermatozoa.

Sperm cells are of unique elongated structure and function, the development of which is tightly regulated by the existing proteins and the posttranslational modifications (PTM) of these proteins. Based on the phylogenetic relationships of various swine breeds, Yorkshire boar is believed to be distinctly different from Duroc boar. The comprehensive differential proteomics and phosphoproteomics profilings were performed on spermatozoa from both Yorkshire and Duroc boars. By both peptide and PTM peptide quantification followed by statistical analyses, 167 differentially expressed proteins were identified from 1,745 proteins, and 283 differentially expressed phosphopeptides corresponding to 102 unique differentially phosphorylated proteins were measured from 1,140 identified phosphopeptides derived from 363 phosphorylated proteins. The representative results were validated by Western blots. Pathway enrichment analyses revealed that majority of differential expression proteins and differential phosphorylation proteins were primarily concerned with spermatogenesis, male gamete generation, sperm motility, energy metabolism, cilium morphogenesis, axonemal dynein complex assembly, sperm–egg recognition, and capacitation. Remarkably, axonemal dynein complex assembly related proteins, such as SMCP, SUN5, ODF1, AKAP3, and AKAP4 that play a key regulatory role in the sperm physiological functions, were significantly higher in Duroc spermatozoa than that of Yorkshire. Furthermore, phosphorylation of sperm-specific proteins, such as CABYR, ROPN1, CALM1, PRKAR2A, and PRKAR1A, participates in regulation of the boar sperm motility mainly through the cAMP/PKA signal pathway in different breeds, demonstrating that protein phosphorylation may be an important mechanism underlying the sperm diversity. Protein–protein interaction analysis revealed that the 14 overlapped proteins between differential expression proteins and differential phosphorylation proteins potentially played a key role in sperm development and motility of the flagellum, including the proteins ODF1, SMCP, AKAP4, FSIP2, and SUN5. Taken together, these physiologically and functionally differentially expressed proteins (DEPs) and differentially expressed phosphorylated proteins (DPPs) may constitute the proteomic backgrounds between the two different boar breeds. The validation will be performed to delineate the roles of these PTM proteins as modulators of Yorkshire and Duroc boar spermatozoa.

Genetic Recombination of the Mantle Color Pattern of Two Boring Giant Clam (Tridacna crocea) Strains

According to the RGB law display, the polymorphism of the giant clam mantle color pattern is through four iridocytes. The boring giant clam (Tridacna crocea) exhibits diverse mantle colors, including blue, green, purple, gold, and orange. In order to evaluate the genetic laws driving these mantle color patterns, a complete diallel cross between two color strains [blue strain (only blue iridocyte) and the yellow-green strain (yellow and green iridocytes)] was performed. Using a single-to-single mating system, two intra-strain crosses (BB and YY) and two reciprocal inter-strain crosses (BY and YB) were produced in triplicates. Higher fertilization rate and hatching rate were observed in all experimental groups, suggesting that there was no sperm–egg recognition barrier between the two strains. In the grow-out stage, the size of the reciprocal hybrids was larger than that of the two pure strains with a degree of heterosis. In addition, compared with the two pure strains, the hybrids have higher larval metamorphosis rate and higher survival rate. At 1 year of age, the mantle color pattern of pure strains showed 100% stable inheritance, while the reciprocal hybrids exhibited colorful patterns (a combination of blue, yellow, and green), suggesting that there was a genetic recombination of the mantle colors during the stable expression period. These results provide a theoretical basis for the formation of the mantle color of giant clam and its genetic segregation law, as well as provide guidance for genetic breeding of giant clams.

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.

Find and fuse: Unsolved mysteries in sperm-egg recognition.

Sexual reproduction is such a successful way of creating progeny with subtle genetic variations that the vast majority of eukaryotic species use it. In mammals, it involves the formation of highly specialised cells: the sperm in males and the egg in females, each carrying the genetic inheritance of an individual. The interaction of sperm and egg culminates with the fusion of their cell membranes, triggering the molecular events that result in the formation of a new genetically distinct organism. Although we have a good cellular description of fertilisation in mammals, many of the molecules involved remain unknown, and especially the identity and role of cell surface proteins that are responsible for sperm–egg recognition, binding, and fusion. Here, we will highlight and discuss these gaps in our knowledge and how the role of some recently discovered sperm cell surface and secreted proteins contribute to our understanding of this fundamental process.

Human sperm chaperone HSPA2 distribution during in vitro capacitation

Human fertilization success depends on the ability of the spermatozoa to undergo capacitation. Even though this process can be conducted in vitro, the optimal time for a sperm cell to complete capacitation in vitro is still under discussion due to the lack of proper capacitation biomarkers. Here, we evaluated the influence of in vitro capacitation time on HSPA2 distribution over human sperm head testing this chaperone as a potential capacitation biomarker. The chaperone was assessed in human spermatozoa from 16 normozoospermic donors using indirect immunofluorescence in uncapacitated, one and four-hour capacitated spermatozoa. The percentage of HSPA2 immunofluorescent cells before and after one hour of capacitation did not differ significantly. However, after four hours of capacitation, we observed a significantly higher percentage of HSPA2 labelled cells. In fluorescent cells analysed before capacitation, we could not identify a predominant distribution pattern. Meanwhile, after capacitation, most sperm showed a highly labelled equatorial band accompanied by a homogeneous fluorescence throughout the acrosomal region. Our findings suggest that HSPA2 needs more than one hour of in vitro capacitation for being correctly distributed in the anterior region of the sperm head. In conclusion, the present study provides solid evidences for the utility of HSPA2 as a biomarker of human sperm in vitro capacitation. Due to its importance during egg-sperm recognition, the use of HSPA2 as a biomarker before an artificial reproduction technique may be suggested, in addition to a longer capacitation time during sperm preparation.