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IZUMO1 is an acrosome transmembrane protein implicated in the adhesion and fusion of gametes. This study aims to describe the distribution of IZUMO1 in human sperm under different physiological conditions: before capacitation (NCS), at one-hour capacitation (CS1), after a hyaluronic acid (HA) selection test (mature, MS1 and immature, IS1), and induced acrosome reaction from one-hour-capacitated sperm (ARS1). The data obtained in NCS, CS1, and MS1 significantly highlight dotted fluorescence in the acrosomal region (P1) as the major staining pattern (~70%). Moreover, we describe a new distribution pattern (P2) with a dotted acrosomal region and a labelled equatorial region that significantly increases in HA-bound spermatozoa, suggesting the onset of the migration of IZUMO1. In contrast, unbound spermatozoa presented an increase in P3 (equatorial region labelled) and P4 (not labelled). Finally, costaining to observe IZUMO1 distribution and acrosome status was performed in ARS1. Interestingly, we reported a variety of combinations between the IZUMO1 staining patterns and the acrosomal stages. In conclusion, these data show as a novelty the diffusion of the IZUMO1 protein during different physiological conditions that could contribute to the improvement in sperm selection techniques.

The failures of binding to the oocyte zona pellucida are commonly attributed to defects in the sperm recognition, adhesion, and fusion molecules. SPAM1 (sperm adhesion molecule 1) is a hyaluronidase implicated in the dispersion of the cumulus-oocyte matrix. Therefore, the aim of this study was to characterize the SPAM1 distribution in the different physiological conditions of human sperm. Specifically, we evaluated the location of the SPAM1 protein in human sperm before capacitation, at one and four hours of capacitation and after hyaluronic acid (HA) selection test by fluorescence microscopy. Sperm bound to HA were considered mature and those that crossed it immature. Our results detected three SPAM1 fluorescent patterns: label throughout the head (P1), equatorial segment with acrosomal faith label (P2), and postacrosomal label (P3). The data obtained after recovering the mature sperm by the HA selection significantly (p < 0.05) highlighted the P1 in both capacitation times, being 79.74 and 81.48% after one hour and four hours, respectively. Thus, the HA test identified that human sperm require the presence of SPAM1 throughout the sperm head (P1) to properly contact the cumulus-oocyte matrix. Overall, our results provide novel insights into the physiological basis of sperm capacitation and could contribute to the improvement of selection techniques.