Progesterone from the Cumulus Cells Is the Sperm Chemoattractant Secreted by the Rabbit Oocyte Cumulus Complex

Abstract

Sperm chemotaxis in mammals have been identified towards several female sources as follicular fluid (FF), oviduct fluid, and conditioned medium from the cumulus oophorus (CU) and the oocyte (O). Though several substances were confirmed as sperm chemoattractant, Progesterone (P) seems to be the best chemoattractant candidate, because: 1) spermatozoa express a cell surface P receptor, 2) capacitated spermatozoa are chemotactically attracted in vitro by gradients of low quantities of P; 3) the CU cells produce and secrete P after ovulation; 4) a gradient of P may be kept stable along the CU; and 5) the most probable site for sperm chemotaxis in vivo could be near and/or inside the CU. The aim of this study was to verify whether P is the sperm chemoattractant secreted by the rabbit oocyte-cumulus complex (OCC) in the rabbit, as a mammalian animal model. By means of videomicroscopy and computer image analysis we observed that only the CU are a stable source of sperm attractants. The CU produce and secrete P since the hormone was localized inside these cells by immunocytochemistry and in the conditioned medium by enzyme immunoassay. In addition, rabbit spermatozoa express a cell surface P receptor detected by western blot and localized over the acrosomal region by immunocytochemistry. To confirm that P is the sperm chemoattractant secreted by the CU, the sperm chemotactic response towards the OCC conditioned medium was inhibited by three different approaches: P from the OCC conditioned medium was removed with an anti-P antibody, the attractant gradient of the OCC conditioned medium was disrupted by a P counter gradient, and the sperm P receptor was blocked with a specific antibody. We concluded that only the CU but not the oocyte secretes P, and the latter chemoattract spermatozoa by means of a cell surface receptor. Our findings may be of interest in assisted reproduction procedures in humans, animals of economic importance and endangered species.

Sperm Chemotaxis: The First Authentication Events Between Conspecific Gametes Before Fertilization

“…Mammalian spermatozoa also show chemotactic behavior, and many candidate chemoattractants for spermatozoa have been proposed (Eisenbach and Giojalas 2006 ). Recently, progesterone released from the cumulus oophorus was considered as a candidate of sperm attractant for human sperm (Guidobaldi et al 2008 ). On the other hand, odorants such as bourgeonal (Spehr et al 2003 ) and lyral (Fukuda et al 2004 ), which are aromatic aldehydes used in perfumes, could also act as chemoattractants in human and mouse sperm, respectively.…”

“…However, no chemotactic cross-reactivity exists in siphonophore species examined, and contact with seawater without attractants is enough to activate sperm motility, although the presence of Ca 2+ ions in seawater is involved in the chemoattraction process (Cosson 1990 ). Mammalian species also seem to share a common sperm attractant molecule (Sun et al 2003 ;Guidobaldi et al 2008 ;Teves et al 2006 ), suggesting the lack of species specifi city. In Mollusca, even though the abalone species seem to show species specifi city in sperm chemotaxis (Riffell et al 2004 ), there is a lack of species specifi city of sperm chemotaxis among chitons (Miller 1977 ).…”

Human sperm pattern of movement during chemotactic re-orientation towards a progesterone source

“…[2][3][4] Follicular fluid, oviductal fluid and the conditioned medium of the egg-cumulus complex are biological sources of chemoattractants. [3][4][5][6][7][8][9][10][11] Follicular fluid that has been obtained from one species may attract spermatozoa of other species, suggesting that chemotaxis may not be a species-specific phenomenon. 12 A small quantity of progesterone, which is secreted by the cells surrounding the egg, is able to attract spermatozoa.…”

“…12 A small quantity of progesterone, which is secreted by the cells surrounding the egg, is able to attract spermatozoa. 7,[13][14][15] The transmembrane adenylyl cyclase-cyclic adenosine mono phosphate-protein kinase A pathway and soluble guanylate cyclase-cyclic guanosine monophosphateprotein kinase G pathway, calcium mobilisation and protein Tyrphosphorylation appear to be involved in the chemotactic response mediated by progesterone. 14 These physiological characteristics of sperm chemotaxis described above, have been primarily observed in human spermatozoa; however, the chemotactic pattern of movement has not been easy to describe.…”

“…Although several molecules have been reported to chemoattract human spermatozoa, 1 progesterone also seems to be of physiological importance. 7,18 This study characterizes human spermatozoa movement pattern during chemotactic re-orientation towards a progesterone source. Such a pattern would facilitate the recognition of the few chemotactic-capacitated spermatozoa, which are cells that have the potential to fertilize the egg.…”