Molecular interplay between sperm and oocyte: a narrative review.

BACKGROUND: Fertilization ensures the transmission of genetic material across generations through a series of precisely coordinated physiological and molecular events. To fertilize an oocyte, a spermatozoon must pass through the cumulus cell layer, penetrate the zona pellucida (ZP), and ultimately adhere to and fuse with the oolemma (the oocyte plasma membrane). Upon fusion, the oocyte initiates mechanisms to block additional sperm entry at both the ZP and oolemma. These processes are highly dynamic in space and time, posing substantial technical barriers to their mechanistic dissection. Nonetheless, recent in silico, in vitro, and in vivo studies have begun to elucidate how intricate networks of intracellular signaling cascades and extracellular protein-protein interactions orchestrate successful fertilization in vertebrates. However, the extent to which these findings accurately reflect the biology of human sperm-oocyte interactions remains obscure, owing to ethical constraints on human gamete experimentation and the limited availability of patients harboring pathogenic variants in fertilization-related genes.

OBJECTIVE AND RATIONALE: This narrative review synthesizes current knowledge of the molecular determinants governing mammalian sperm-oocyte interactions, summarizes relevant genetic anomalies identified in infertile patients, and discusses emerging experimental approaches for the direct investigation of human fertilization. We also explore how recent mechanistic insights and technological innovations may inform the diagnosis and treatment of fertilization disorders and guide the development of novel contraceptive strategies.

SEARCH METHODS: We searched PubMed, Google Scholar, and Scopus to identify research and review articles published in English. Studies limited to non-mammalian species and non-peer-reviewed preprints were excluded. Searches used terms related to fertilization, sperm-oocyte interactions, ZP, cumulus cells, polyspermy block, and human infertility, alone or in combination. Additional searches targeted key proteins and emerging technologies relevant to mammalian fertilization, clinical diagnostics, and contraceptive development.

OUTCOMES: Our mechanistic understanding of mammalian gamete interactions has predominantly stemmed from in vitro and in vivo animal studies, which have revealed key molecular processes, such as sperm hyaluronidase-mediated cumulus matrix dispersal, translocation of sperm acrosomal membrane proteins to enable oolemma interaction, and ZP glycoprotein cleavage underlying the polyspermy block. While studies in model species remain indispensable, translating this knowledge to human biology requires meticulous validation. The integration of interdisciplinary approaches, such as humanized mouse models, artificial human oocytes, xenospecies fertilization assays, antibody inhibition studies, and high-throughput interactome screening, offers promising avenues to clarify interspecies discrepancies and generate insights more directly relevant to human gamete interactions.

WIDER IMPLICATIONS: Advances in the mechanistic dissection of sperm-oocyte interactions are anticipated to support the development of diagnostic tools and therapeutic interventions for infertility caused by defective fertilization. In parallel, these discoveries may enable the rational design of safe, reversible contraceptives that selectively block gamete interactions without compromising other physiological processes.

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