Binder of SPerm (BSP) proteins are ubiquitous amongst mammals and are exclusively expressed in male genital tract. The main function associated with BSP proteins is their ability to promote sperm capacitation. Two genes (Bsph1 and Bsph2) coding for BSP proteins have been identified in murine epididymis. Recent studies performed in our laboratory demonstrated using recombinant proteins that rec-BSPH1 and rec-BSPH2 could bind to epididymal sperm membranes, but only rec-BSPH1 had the ability to promote sperm capacitation in vitro. The goal of the present study was to evaluate the role of native murine BSP proteins in in vitro sperm capacitation, using conditions closer to those observed in vivo. Follicular and oviductal fluids contain High-Density Lipoproteins (HDL). HDL is known to extract cholesterol from sperm membranes, increase levels of tyrosine phosphorylation of signaling proteins and induce sperm capacitation in vitro. Therefore, we tested the effect of antibodies and antigen-binding fragments (Fabs) specific to murine BSP proteins on capacitation induced by HDL. Results obtained show that antibodies and Fabs could block capacitation induced by HDL and could inhibit the HDL-induced increase in tyrosine phosphorylation. These results suggest that a specific interaction between HDL and BSP proteins in mice could be necessary for sperm capacitation. To this day, only one other family of proteins (cholesterol transporters) has been shown to be important for HDL-induced capacitation. Based on the results obtained, it is possible that BSP proteins in mice could be a new important piece of the puzzle to understand sperm capacitation and the processes leading to fertilization. A BSP protein, orthologous to murine BSPH1, has also been identified in human (BSPH1). This study of BSP proteins using a mouse model could also give new insights on the functions and the importance of the human protein in male fertility.  (Supported by CIHR and FRQS)