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

María Jiménez-Movilla,Raquel Romar,Julieta G Hamze

doi:10.3389/fcell.2021.662032

Abstract

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.

Highlights

To generate a new, unique, and diploid individual with the totipotent capacity to develop a speciesspecific organism, two highly differentiated haploid cells from each progenitor, the egg, and the sperm, must recognize themselves and bind and fuse
A series of distinct membrane events must occur for two cells to fuse and merge their cytoplasmic content. All these phenomena entail the involvement of specific molecules and the activation of molecular cascades that appropriately coordinate all the cellular events that gamete recognition, binding, and fusion involve
CD81-deficient female mice (CD81−/−) presented a 40% reduction in fertility, and in vitro fertilization (IVF) assays suggested that this phenotype is due to a failure in sperm–egg fusion

Summary

INTRODUCTION

Unique, and diploid individual with the totipotent capacity to develop a speciesspecific organism, two highly differentiated haploid cells from each progenitor, the egg, and the sperm, must recognize themselves and bind and fuse This event, termed fertilization, results into the generation of a zygote and involves several stages in which different molecular processes must trigger the cellular activity of the gametes. A series of distinct membrane events must occur for two cells to fuse and merge their cytoplasmic content All these phenomena entail the involvement of specific molecules and the activation of molecular cascades that appropriately coordinate all the cellular events that gamete recognition, binding, and fusion involve. The presence of CD9 and CD81 has been recently described in the sperm head, over the acrosome and in the plasma membrane, respectively, suggesting once

New Methods to Study Mammalian Molecular Fertilization

Findings

CONCLUSION