Location and expression of Juno in mice oocytes during maturation

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.

Sperm induction of somatic cell-cell fusion as a novel functional test

The fusion of mammalian gametes requires the interaction between IZUMO1 on the sperm and JUNO on the oocyte. We have recently shown that ectopic expression of mouse IZUMO1 induces cell-cell fusion and that sperm can fuse to fibroblasts expressing JUNO. Here, we found that the incubation of mouse sperm with hamster fibroblasts or human epithelial cells in culture induces the fusion between these somatic cells and the formation of syncytia, a pattern previously observed with some animal viruses. This sperm-induced cell-cell fusion requires a species-matching JUNO on both fusing cells, can be blocked by an antibody against IZUMO1, and does not rely on the synthesis of new proteins. The fusion is dependent on the sperm's fusogenic capacity, making this a reliable, fast, and simple method for predicting sperm function during the diagnosis of male infertility.

Selective reprogramming of regulatory T cells in solid tumors can strongly enhance or inhibit tumor growth

Folate receptor delta (FRδ) has been used as a biomarker for regulatory T cells (Tregs), because its expression is limited to Tregs and ovum. Although FRδ is unable to bind folate, we have used molecular docking software to identify a folate congener that binds FRδ with high affinity and have exploited this FRδ-specific ligand to target attached drugs (imaging agents, immune activators, and immune suppressors) specifically to Tregs in murine tumor xenografts. Analysis of treated tumors demonstrates that targeting of a Toll-like receptor 7 agonist inhibits Treg expression of FOXP3, PD-1, CTLA4, and HELIOS, resulting in 40-80% reduction in tumor growth and repolarization of other tumor-infiltrating immune cells to more inflammatory phenotypes. Targeting of the immunosuppressive drug dexamethasone, in contrast, promotes enhanced tumor growth and shifts the tumor-infiltrating immune cells to more anti-inflammatory phenotypes. Since Tregs comprise <1% of cells in the tumor masses examined, and since the targeted drugs are not internalized by cancer cells, these data demonstrate that Tregs exert a disproportionately large effect on tumor growth. Because the targeted drug did not bind to Tregs or other immune cells in healthy tissues, the data demonstrate that the immunosuppressive properties of Tregs in tumors can be manipulated without causing systemic toxicities associated with global reprogramming of the immune system.

Oolemma Receptors in Mammalian Molecular Fertilization: Function and New Methods of Study

Fertilization is a key process in biology to the extent that a new individual will be born from the fusion of two cells, one of which leaves the organism in which it was produced to exert its function within a different organism. The structure and function of gametes, and main aspects of fertilization are well known. However, we have limited knowledge about the specific molecules participating in each of the steps of the fertilization process due to the transient nature of gamete interaction. Moreover, if we specifically focus in the fusion of both gametes’ membrane, we might say our molecular knowledge is practically null, despite that molecular mechanisms of cell-to-cell adhesion are well studied in somatic cells. Moreover, between both gametes, the molecular knowledge in the egg is even scarcer than in the spermatozoon for different reasons addressed in this review. Sperm-specific protein IZUMO1 and its oocyte partner, JUNO, are the first cell surface receptor pair essential for sperm–egg plasma membrane binding. Recently, thanks to gene editing tools and the development and validation of in vitro models, new oocyte molecules are being suggested in gamete fusion such as phosphatidylserine recognition receptors. Undoubtedly, we are in a new era for widening our comprehension on molecular fertilization. In this work, we comprehensively address the proposed molecules involved in gamete binding and fusion, from the oocyte perspective, and the new methods that are providing a better understanding of these crucial molecules.

Perfect date-the review of current research into molecular bases of mammalian fertilization

Fertilization is a multistep process during which two terminally differentiated haploid cells, an egg and a sperm, combine to produce a totipotent diploid zygote. In the early 1950s, it became possible to fertilize mammalian eggs in vitro and study the sequence of cellular and molecular events leading to embryo development. Despite all the achievements of assisted reproduction in the last four decades, remarkably little is known about the molecular aspects of human conception. Current fertility research in animal models is casting more light on the complexity of the process all our lives start with. This review article provides an update on the investigation of mammalian fertilization and highlights the practical implications of scientific discoveries in the context of human reproduction and reproductive medicine.