{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n CRISP2 (also known as TPX‐1) is a testis‐enriched, cysteine‐rich secretory protein expressed specifically in haploid germ cells and incorporated into developing sperm, where it localizes primarily to the acrosome and flagellum. Functional studies in both mouse and human systems demonstrate that CRISP2 remains associated with sperm even after capacitation and the acrosome reaction, suggesting an active role during the later stages of fertilization. In vitro and in vivo investigations indicate that CRISP2 facilitates gamete fusion by binding directly to complementary sites on the egg surface and may help modulate calcium ion flux through interactions with ryanodine receptors and ion channels such as CATSPER1—processes critical for triggering the acrosome reaction and establishing proper flagellar motility."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n In support of its role in sperm–egg interaction, antibody blocking and recombinant protein competition assays in both rodents and humans lead to significant reductions in sperm penetration of the egg, without affecting sperm motility or acrosome reaction per se. Moreover, studies using yeast two‐hybrid screening have identified novel CRISP2‐binding partners that may further modulate its function during sperm maturation."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Clinically, reduced CRISP2 protein levels—frequently occurring without corresponding decreases in mRNA—and aberrant posttranscriptional regulation by microRNAs (such as miR‐27a and miR‐27b) have been correlated with impaired sperm motility and abnormal morphology, conditions observed in asthenozoospermic or asthenoteratozoospermic patients."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "5", "end_ref": "8"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Together, these findings support a model in which CRISP2 acts as a key modulator of fertilization by ensuring proper acrosome function, mediating the fusion process, and contributing to the regulation of sperm motility. Its dysfunction—whether by genetic ablation or by posttranscriptional down‐regulation—leads to compromised fertilizing ability, underscoring its importance in male fertility."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}, {"type": "fg_f", "ref": "9"}]}, {"type": "t", "text": "\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Dolores Busso, Nadia M Goldweic, Masaru Hayashi, et al. 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