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

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.

Cell–Cell Mating Interactions: Overview and Potential of Single-Cell Force Spectroscopy

“…Nevertheless, in all organisms, the process requires two characteristics: specificity of the interaction and a long enough contact time to ensure cellular fusion and/or gene transfer. Because mating systems are both complex and fastevolving [9][10][11][12][13][14], there are a wide variety of strategies to achieve these characteristics.…”

“…In mammalian fertilization, the zona pellucida proteins and the Izumo1/Juno pairs are known to be essential for binding and fertilization [13]. The egg protein ZP2 is a zona pellucida protein required for species-specific sperm recognition, and sperm binding triggers polyspermy blocking activities.…”