Stromal cell-derived factor 1 regulates in vitro sperm migration towards the cumulus-oocyte complex in cattle

Abstract

Sperm migration towards an oocyte in the female reproductive tract is an important step for successful fertilization. Although several sperm-chemotactic factors have been identified in mammals, it is unclear whether these chemoattractants contribute to sperm migration towards an oocyte that is the final destination for sperm. Furthermore, chemoattractants for bovine sperm are still undiscovered even though the follicular fluid attracts sperm in cattle. Here, we demonstrated that a single bovine cumulus-oocyte complex (COC) had the ability to attract sperm, suggesting that the COC secreted sperm chemoattractants. We identified stromal cell-derived factor 1 (SDF1), which was expressed in COCs, and its receptor CXCR4 in sperm, as a candidate. Our results showed that bovine sperm preferentially migrated to the area with a high SDF1 concentration and occasionally showed turn movements by asymmetric flagellar bends during the migration. We also demonstrated that increasing the intracellular Ca 2+ concentration via Ca 2+ channels was related to SDF1induced sperm chemotaxis. Finally, a CXCR4 inhibitor significantly suppressed the in vitro bovine sperm migration towards a COC. Taken together, we propose that SDF1 is a chemotactic factor for bovine sperm to regulate their migration towards an oocyte via the CXCR4 receptor.

In Vitro Maturation of Cumulus–Oocyte Complexes and In Vitro Sperm Capacitation Significantly Increase the Expression and Enhance the Location of the CXCL12 and CXCR4 Anchoring Attractant Complex in Pigs

“…Both the follicular fluid and the cumulus cells are known to secrete a variety of chemokines that promote sperm hyperactivity and increase sperm motility following receptor binding [ 35 , 36 ]. One of the reported cytokines, CXCL12, is able, moreover, to build a complex with CXCR4 (the CXCL12–CXCR4 complex), which has been described as one of the main mechanisms to promote sperm chemotaxis towards the COC [ 22 ], although its location in the participating cell types might also represent a specific anchoring mechanism during fertilization, perhaps even selecting/favoring only the capacitated spermatozoa to engage in ZP-binding and further fertilization.…”

“…Our results show that CXCL12 is produced in the cumulus cells cytoplasm, from where it may act as a sperm chemoattractant prior to fertilization. Previous studies reported that CXCL12 is locally produced by cumulus cells from human [ 21 ], cattle [ 22 ], and sheep oocytes [ 23 ]. Furthermore, besides its role in oocyte maturation, a recent study in cattle [ 22 ] suggested that a single COC has the ability to attract spermatozoa towards the oocyte, pointing to CXCL12 as the main sperm chemoattractant candidate, which would interact with its receptor (CXCR4) if localized in the spermatozoa.…”

“…CXCL12 was previously reported to be produced by cumulus cells from human [ 21 ], cattle [ 22 ], and sheep oocytes [ 23 ], with its receptor (CXCR4) being localized in the head or tail of human [ 24 ] and bovine [ 22 ] spermatozoa.…”

Characteristics and Possible Role of Bovine Sperm Head-to-Head Agglutination

“…To compare the quality of mitochondrial function between agglutinated and unagglutinated sperm, the mitochondrial membrane potential (MMP) of sperm was evaluated by 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolylcarbocyanine iodide (JC-1) staining using a commercially available kit as reported previously (MitoProbe TM JC-1 Assay Kit, Thermo Fisher Scientific) [ 20 ]. Briefly, sperm suspension was incubated in non-capacitation medium for 0, 5 or 24 h at 38.5 °C with 5% CO 2 .…”

Expanding the Limits of Computer-Assisted Sperm Analysis through the Development of Open Software

“…Thus, the study of sperm behavior and its ability to react to external stimuli could be used as an indicator of sperm quality, and could help to predict the fertility of a given seminal sample, assisted by computer automation. One of the most studied mechanisms involved in sperm guidance is chemotaxis, or the directed movement of sperm in response to a chemical gradient [ 23 , 24 ]. Due to the lack of a specific tool in both commercial and open source systems, the first version of OpenCASA included a module for sperm guided movement analysis [ 10 ].…”