Sperm-oocyte signaling: the role of IZUMO1R and CD9 in PTK2B activation and actin remodeling at the sperm binding site†

Noncanonical phagocytosis-like SEAL establishes mammalian fertilization

In many forms of sexual reproduction, only the most robust spermatozoa, which overcome multiple physiological challenges, reach the oocyte. However, the exact mechanisms of gamete recognition and fusion are unknown. In the present study, we demonstrated that with the onset of gamete recognition, oocyte microvilli form lamellipodium-like structures, activate actin polymerization, and subsequently engulf spermatozoa to initiate gamete fusion. Gamete fusion occurred via a phagocytosis-like process we termed "sperm engulfment activated by IZUMO1-JUNO linkage and gamete fusion-related factors" (SEAL). Gamete adhesion was strictly regulated by binding of sperm IZUMO1 to oocyte JUNO, while SEAL was primarily mediated by sperm DCST1/2, SPACA6, TMEM95, FIMP, and TMEM81, the essential factors for gamete fusion. Interestingly, JUNO was almost depleted from oocyte surfaces in the region where SEAL enveloped spermatozoa by microvilli without actin polymerization. SEAL formation was recapitulated using JUNO-expressing K562 lymphocytic cells rather than oocytes. Together, these findings suggest that dynamic rearrangement of membrane components facilitates SEAL prior to successful fertilization.

Updating the Role of JUNO and Factors Involved in Its Function during Fertilization

INTRODUCTION

The final step of the fertilization process involves gametes adhesion and fusion. JUNO is an essential folate receptor 4 protein present in the ooplasm of oocytes, which binds to IZUMO1, its receptor on the sperm surface. Both proteins are indispensable for the sperm-oocyte interaction, and their absence results in infertility. Despite the importance of JUNO in reproduction, there is still controversy about how different factors affect the functionality of JUNO. Therefore, the goal of this study was to provide a comprehensive overview of what we know so far about the presence and functionality of JUNO.

METHODS

In order to accomplish this, a total of 198 articles were identified. Based on both inclusion and exclusion criteria, 40 articles were finally included in this study.

RESULTS

The results showed that during oocyte maturation, the expression levels of JUNO undergo alterations and, in some instances, cross-species gamete fusion is possible. Additionally, it has been observed that exposure of oocytes to factors such as bisphenol A, 17α-ethynylestradiol, diazinon, benzo(a)pyrene, butylparaben, bis(2-ethylhexyl) phthalate, hydroxyurea, dichlorophenol, isoniazid, and para-phenylenediamine disrupt JUNO and decrease the fertilization process rates. Moreover, exposure to ionic radiation, vitrification, and synthetic materials as microplastics has the same effect. Nonetheless, other compounds such as melatonin, mogroside V, cholesterol-loaded methyl-β-cyclodextrin, methyl-β-cyclodextrin, protocatechuic acid, coenzyme Q10, resveratrol, and Shoutai pills have been shown to enhance female fertility in terms of JUNO functionality.

CONCLUSION

In summary, this update highlights the crucial role of JUNO during fertilization and reveals how different factors and experimental procedures affect its activity.

Paternal contributions to mammalian zygote - Beyond sperm-oocyte fusion

Contrary to a common misconception that the fertilizing spermatozoon acts solely as a vehicle for paternal genome delivery to the zygote, this chapter aims to illustrate how the male gamete makes other essential contributions , including the sperm borne-oocyte activation factors, centrosome components, and components of the sperm proteome and transcriptome that help to lay the foundation for pregnancy establishment and maintenance to term, and the newborn and adult health. Our inquiry starts immediately after sperm plasma membrane fusion with its oocyte counterpart, the oolemma. Parallel to and following sperm incorporation in the egg cytoplasm, some of the sperm structures (perinuclear theca) are dissolved and spent to induce development, others (nucleus, centriole) are transformed into zygotic structures enabling it, and yet others (mitochondrial and fibrous sheath, axonemal microtubules and outer dense fibers) are recycled as to not stand in its way. Noteworthy advances in this research include the identification of several sperm-borne oocyte activating factor candidates, the role of autophagy in the post-fertilization sperm mitochondrion degradation, new insight into zygotic centrosome origins and function, and the contributions of sperm-delivered RNA cargos to early embryo development. In concluding remarks, the unresolved issues, and clinical and biotechnological implications of sperm-vectored paternal inheritance are discussed.

Identified Candidate Genes of Semen Trait in Three Pig Breeds Through Weighted GWAS and Multi-Tissue Transcriptome Analysis

High-quality semen is an essential factor for the success of artificial insemination, and revealing the genetic structure of pig semen traits helps improve semen quality. This study aimed to identify candidate genes associated with semen traits in three pig breeds (Duroc, Landrace, and Yorkshire) through weighted GWAS and multi-tissue transcriptome analysis. In this study, to identify candidate genes associated with semen traits in Duroc, Landrace, and Yorkshire, we performed weighted GWAS in four traits (sperm motility, sperm progressive motility, sperm abnormality rate, and total sperm count) using 936 pigs and multi-tissue transcriptome analysis using 34 tissues RNA-seq data of 5457 pigs from FarmGTEx. It was found that 16, 9, and 12 significant SNPs associated with semen traits were identified in Duroc, Landrace, and Yorkshire, with corresponding 7, 5, and 7 candidate genes in these three breeds, respectively, which may be involved in mammal spermatogenesis, testicular function, and male fertility. Moreover, we not only found the same candidate gene DNAI2 as in previous studies but also found two new candidate genes PNLDC1 and RSPH3, which were identified simultaneously in both Landrace and Yorkshire. By integrating the GWAS and multi-tissue transcriptome analysis results, we found that candidate genes associated with semen traits of three pig breeds were highly expressed in the testis tissue. The three genotypes of rs320928244 had significant effects on the expression of the DYNLT1 gene in the testis tissue of Landrace. These results together showed that these candidate genes were mainly related to sperm motility defects. This study helps deepen the understanding of the genetic basis of semen traits and provides a theoretical foundation for improving the semen quality of Duroc, Landrace, and Yorkshire breeds.

Systemic low-dose anti-fibrotic treatment attenuates ovarian aging in the mouse

The female reproductive system is one of the first to age in humans, resulting in infertility and endocrine disruptions. The aging ovary assumes a fibro-inflammatory milieu which negatively impacts gamete quantity and quality as well as ovulation. Here, we tested whether the systemic delivery of anti-inflammatory (Etanercept) or anti-fibrotic (Pirfenidone) drugs attenuates ovarian aging in mice. We first evaluated the ability of these drugs to decrease the expression of fibro-inflammatory genes in primary ovarian stromal cells treated with a pro-fibrotic or a pro-inflammatory stimulus. Whereas Etanercept did not block Tnf expression in ovarian stromal cells, Pirfenidone significantly reduced Col1a1 expression. We then tested Pirfenidone in vivo where the drug was delivered systemically via mini-osmotic pumps for 6 weeks. Pirfenidone mitigated the age-dependent increase in ovarian fibrosis without impacting overall health parameters. Ovarian function was improved in Pirfenidone-treated mice as evidenced by increased follicle and corpora lutea number, AMH levels, and improved estrous cyclicity. Transcriptomic analysis revealed that Pirfenidone treatment resulted in an upregulation of reproductive function-related genes at 8.5 months and a downregulation of inflammatory genes at 12 months of age. These findings demonstrate that reducing the fibroinflammatory ovarian microenvironment improves ovarian function, thereby supporting modulating the ovarian environment as a therapeutic avenue to extend reproductive longevity.

Systemic low-dose anti-fibrotic treatment attenuates ovarian aging in the mouse

The female reproductive system is one of the first to age in humans, resulting in infertility and endocrine disruptions. The aging ovary assumes a fibro-inflammatory milieu which negatively impacts gamete quantity and quality as well as ovulation. Here we tested whether the systemic delivery of anti-inflammatory (Etanercept) or anti-fibrotic (Pirfenidone) drugs attenuates ovarian aging in mice. We first evaluated the ability of these drugs to decrease the expression of fibro-inflammatory genes in primary ovarian stromal cells. Whereas Etanercept did not block Tnf expression in ovarian stromal cells, Pirfenidone significantly reduced Col1a1 expression. We then tested Pirfenidone in vivo where the drug was delivered systemically via mini-osmotic pumps for 6-weeks. Pirfenidone mitigated the age-dependent increase in ovarian fibrosis without impacting overall health parameters. Ovarian function was improved in Pirfenidone-treated mice as evidenced by increased follicle and corpora lutea number, AMH levels, and improved estrous cyclicity. Transcriptomic analysis revealed that Pirfenidone treatment resulted in an upregulation of reproductive function-related genes at 8.5 months and a downregulation of inflammatory genes at 12 months of age. These findings demonstrate that reducing the fibroinflammatory ovarian microenvironment improves ovarian function, thereby supporting modulating the ovarian environment as a therapeutic avenue to extend reproductive longevity.

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.

Study on the expression patterns and function of JUNO and CD9 in bovine oocytes during in vitro maturation

Fertilization proteins JUNO and CD9 play vital roles in sperm-egg fusion, but little is known about their expression patterns during in vitro maturation (IVM) and their function during in vitro fertilization (IVF) of bovine oocytes. In this study, qRT-PCR and immunofluorescence staining were used to detect the mRNA and protein expression levels of JUNO and CD9 genes in bovine oocytes and cumulus cells. Then, fertilization rate of MII oocytes treated with (i) JUNO antibody (1, 5 and 25 μg/ml) or (ii) CD9 antibody (1, 5 and 25 μg/ml) or (iii) CD9 antibody (5 μg/ml) + JUNO antibody (5 μg/ml) were recorded. Our results showed that the mRNA and protein expression levels of JUNO and CD9 genes significantly increased from bovine GV oocytes to MII oocytes, and similar mRNA expression patterns of JUNO and CD9 were also detected in cumulus cells. All groups of oocytes treated with CD9 antibody or JUNO antibody showed significantly decreased fertilization rates (p < .05). Particularly, the fertilization ability of oocytes treated with CD9 antibody (5 μg/ml) + JUNO antibody (5 μg/ml) sharply decreased to 3.48 ± 0.11%. In conclusion, our study revealed the expression levels of JUNO and CD9 genes in oocytes and cumulus cells increased during IVM of bovine oocytes, with JUNO protein playing a major role in the fertilization of bovine oocytes.

Transcriptional Specificity Analysis of Testis and Epididymis Tissues in Donkey

Donkeys, with high economic value for meat, skin and milk production, are important livestock. However, the current insights into reproduction of donkeys are far from enough. To obtain a deeper understanding, the differential expression analysis and weighted gene co-expression network analysis (WGCNA) of transcriptomic data of testicular and epididymis tissues in donkeys were performed. In the result, there were 4313 differentially expressed genes (DEGs) in the two tissues, including 2047 enriched in testicular tissue and 2266 in epididymis tissue. WGCNA identified 1081 hub genes associated with testis development and 6110 genes with epididymal development. Next, the tissue-specific genes were identified with the above two methods, and the gene ontology (GO) analysis revealed that the epididymal-specific genes were associated with gonad development. On the other hand, the testis-specific genes were involved in the formation of sperm flagella, meiosis period, ciliary assembly, ciliary movement, etc. In addition, we found that eca-Mir-711 and eca-Mir-143 likely participated in regulating the development of epididymal tissue. Meanwhile, eca-Mir-429, eca-Mir-761, eca-Mir-200a, eca-Mir-191 and eca-Mir-200b potentially played an important role in regulating the development of testicular tissue. In short, these results will contribute to functional studies of the male reproductive trait in donkeys.

Changes in cortical endoplasmic reticulum clusters in the fertilized mouse oocyte†

Oocytes from many invertebrate and vertebrate species exhibit unique endoplasmic reticulum (ER) specializations (cortical ER clusters), which are thought to be essential for egg activation. In examination of cortical ER clusters, we observed that they were tethered to previously unreported fenestrae within the cortical actin layer. Furthermore, studies demonstrated that sperm preferentially bind to the plasma membrane overlying the fenestrae, establishing close proximity to underlying ER clusters. Moreover, following sperm-oocyte fusion, cortical ER clusters undergo a previously unrecognized global change in volume and shape that persists through sperm incorporation, before dispersing at the pronuclear stage. These changes did not occur in oocytes from females mated with Izumo1 -/- males. In addition to these global changes, highly localized ER modifications were noted at the sperm binding site as cortical ER clusters surround the sperm head during incorporation, then form a diffuse cloud surrounding the decondensing sperm nucleus. This study provides the first evidence that cortical ER clusters interact with the fertilizing sperm, indirectly through a previous unknown lattice work of actin fenestrae, and then directly during sperm incorporation. These observations raise the possibility that oocyte ER cluster-sperm interactions provide a competitive advantage to the oocyte, which may not occur during assisted reproductive technologies such as intracytoplasmic sperm injection.

Signaling Proteins Recruited to the Sperm Binding Site: Role of β-Catenin and Rho A

Sperm interaction with the oocyte plasma membrane triggers a localized response in the mouse oocyte that leads to remodeling of oocyte surface as well as the underlying cortical actin layer. The recent demonstration that PTK2B is recruited and activated at the sperm binding site raised the possibility that multiple signaling events may be activated during this stage of fertilization. The present study demonstrated that β-catenin and Rho A were recruited to the cortex underlying bound/fused sperm. To determine whether sperm-oocyte contact was sufficient to initiate β-catenin recruitment, Cd9-null, and PTK2b-null oocytes were tested for the ability to recruit β-catenin to sperm binding sites. Both Cd9 and Ptk2b ablation reduced β-catenin recruitment raising the possibility that PTK2B may act downstream of CD9 in the response to sperm binding/fusion. Further immunofluorescence study revealed that β-catenin co-localized with f-actin in the interstitial regions between actin layer fenestrae. Rho A, in contrast, was arranged underneath the actin layer in both the fenestra and the interstitial regions suggesting that they may play different roles in the oocyte.

Microbially Catalyzed Biomaterials for Bone Regeneration

Bone is a complex mineralized tissue composed of various organic (proteins, cells) and inorganic (hydroxyapatite, calcium carbonate) substances with micro/nanoscale structures. To improve interfacial bioactivity of bone-implanted biomaterials, extensive efforts are being made to fabricate favorable biointerface via surface modification. Inspired by microbially catalyzed mineralization, a novel concept to biologically synthesize the micro/nanostructures on bioceramics, microbial-assisted catalysis, is presented. It involves three processes: bacterial adhesion on biomaterials, production of CO₃ ^2- assisted by bacteria, and nucleation and growth of CaCO₃ nanocrystals on the surface of bioceramics. The microbially catalyzed biominerals exhibit relatively uniform micro/nanostructures on the surface of both 2D and 3D α-CaSiO₃ bioceramics. The topographic and chemical cues of the grown micro/nanostructures present excellent in vitro and in vivo bone-forming bioactivity. The underlying mechanism is closely related to the activation of multiple biological processes associated with bone regeneration. The study offers a microbially catalytic concept and strategy of fabricating micro/nanostructured biomaterials for tissue regeneration.

The Fertilization Enigma: How Sperm and Egg Fuse

Fertilization is a multistep process that culminates in the fusion of sperm and egg, thus marking the beginning of a new organism in sexually reproducing species. Despite its importance for reproduction, the molecular mechanisms that regulate this singular event, particularly sperm-egg fusion, have remained mysterious for many decades. Here, we summarize our current molecular understanding of sperm-egg interaction, focusing mainly on mammalian fertilization. Given the fundamental importance of sperm-egg fusion yet the lack of knowledge of this process in vertebrates, we discuss hallmarks and emerging themes of cell fusion by drawing from well-studied examples such as viral entry, placenta formation, and muscle development. We conclude by identifying open questions and exciting avenues for future studies in gamete fusion. Expected final online publication date for the Annual Review of Cell and Developmental Biology, Volume 37 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.