Modulation of spermatozoa and zona pellucida properties by the soluble acrosome reaction-inducing factor of the ovulated egg-cumulus complex

Egg-cumulus-oviduct interactions and fertilization

In this communication we approach the events leading to fertilization in mammals by examining the triangle of egg, sperm and oviductal cell taking account of the local physiology and focussing on auto/paracrine interactions. The expression of growth factors and extra-cellular matrix (ECM)-components in bovine ovarian granulosa- and theca-cells, the oocyte-cumulus complex (OOC) and oviductal epithelium, as well as some of the corresponding secreted proteins can be detected through the estrous cycle. Components of the insulin-like (IGF), fibroblast (FGF) and transforming (TGF) growth factor systems, and also metalloproteinase 1 (MMP1) and urokinase (uPA) are found to be modulated in these cells prior to fertilization. Different expression levels between the cell types are found, each representative of a specific reaction window within that particular stage of the cycle. Our findings support the concept that most of the observed tissue in the reproductive tract is dependent upon on the effects of gonadotropins or steroids, but that the fine-regulation is conveyed by, for example, growth factors and ECM-components. We suggest a sophisticated, auto/paracrine and species-specific crosstalk of growth factors and ECM components between the different cell types involved, enabling fertilization and development of the embryo at the right time and in the right location.

Kinetics of sperm penetration and fertilization in vitro in hamster follicular and oviductal ova

This study compared kinetics of in vitro sperm penetration and fertilization of in vivo matured follicular vs. oviductal hamster ova. Monospermic fertilization in cumulus-intact (C+) and cumulus-free (C-) follicular ova was highest at sperm concentrations of approximately 50 and 1.0 x 10(4) sperm/ml, respectively. The cumulus layer was a barrier to sperm penetration, but penetration of C-follicular ova was still lower than with C-oviductal ova. At 1 h of sperm:egg coincubation, 21% of C- follicular ova was penetrated vs. 77% of C- oviductal ova, while by 4 h these values were 71% and 98%, respectively. In contrast, activation of zona-free follicular and oviductal ova was not different (83-99%). However, at 2 h male pronuclear formation was lower in follicular ova (9%) than in oviductal ova (26%, P < 0.05). To test the hypothesis that lower and slower penetration with follicular ova compared with oviductal ova is due to lack of oviductal exposure, effects of hamster periovulatory oviductal fluid on penetration and fertilization kinetics of C- follicular ova were examined. Adding oviductal fluid did not improve penetration of follicular ova to levels equivalent to oviductal ova, but 3 h preincubation of follicular ova with oviductal fluid improved both zona penetration and male pronucleus formation to levels equivalent to those in oviductal ova. We conclude that kinetics of sperm penetration and fertilization in follicular ova are retarded, that these deficiencies derive from lack of ovum modulation by oviductal secretions, and that prolonged oviductal exposure of ova is essential for achieving full competence.

Messenger RNA encoding an estrogen-dependent oviduct secretory protein in the sheep is localized in the apical tips and basal compartments of fimbria and ampulla epithelial cells implying translation at unique cytoplasmic foci

Data from our laboratory have shown that an estrogen (E2)-dependent M(r) 90,000-92,000 protein and its mRNA are synthesized and expressed in abundant amounts at estrus from the fimbria and ampulla, not isthmus, oviduct of the sheep. Immunocytochemical studies have shown that the M(r) 90,000-92,000 protein is contained in apical secretory granules of oviduct epithelial cells. The objective of this study was to determine whether the mRNA for the E2-dependent oviduct protein was localized and compartmentalized in similar manner. Fimbria, ampulla, and isthmus oviducts obtained from estrous ewes were flash frozen in liquid nitrogen, cryosectioned, fixed in 4% paraformaldehyde, hybridized with digoxigenin (DIG)-labeled oviduct-specific riboprobes, incubated in anti-DIG antibodies conjugated with alkaline phosphatase, and developed in color substrate. Oviduct protein-specific transcripts were localized to basal perinuclear compartments and, surprisingly, at sites distant from the nucleus in the apical cytoplasm of epithelial cells in the fimbria and ampulla. No specific reaction product was observed in the underlying mucosa or smooth muscle layers. Oviduct protein mRNA was contained predominantly in the apical cytoplasm of epithelial cells at the free margins of mucosal folds and in the basal regions of cells located at the crypts of longitudinal folds. No reaction product was present when sections of the fimbria and ampulla oviduct of estrous ewes were incubated in sense riboprobe to the oviduct protein. In addition, when sections of the isthmus oviduct obtained from estrous ewes or fimbira and ampulla oviducts from long-term ovariectomized ewes were hybridized with antisense riboprobes no specific reaction product was detected. Electron microscopy of oviduct protein mRNA containing areas revealed the presence of secretory granules, rough endoplasmic reticulum (RER) and Golgi in the apical cytoplasm, and RER in the basal regions of epithelial cells. These data show that the mRNA encoding an E2-dependent oviduct-specific protein is distributed in epithelial cells at perinuclear foci and at sites distant from the nucleus, which are also the sites of protein localization and protein synthesizing organelles, implying translation at unique cytoplasmic foci.

Oviductins possess chitinase- and mucin-like domains: a lead in the search for the biological function of these oviduct-specific ZP-associating glycoproteins

Over the last 10 years considerable progress has been made in the immunological and biochemical characterization of oviduct-specific glycoproteins. It is now well established that a subclass of these secretory products, designated as oviductins, associate with the zona pellucida of the ovulated oocyte and with the early embryo. Recent reports on the cloning of cDNAs of oviductins from various species, including that of golden hamster (Mesocricetus auratus) oviductin by our laboratory, allowed us to compare their deduced amino acid sequences with those of other proteins. Optimal alignment analysis showed that oviductins contain regions of significant similarity with catalytically inactive mammalian members of the bacterial and microfilarial chitinase protein family. Most importantly, a close examination of the hamster and human deduced amino acid sequences revealed that both glycoproteins possess contiguous Ser/Thr rich repeated units, clustered in their carboxy-terminal portions. These mucin-type motifs are similar in the hamster and human glycoprotein, although hamster oviductin contains more of these complete units. This striking feature might indicate that these molecules play a similar role to mucin-type glycoproteins, e.g., in protecting the oocyte and early embryo against attacks from their environment. We propose a model whereby oviductins are targeted to the oocyte via the interaction of their chitinase-like domains with specific oligosaccharide moieties of the zona pellucida. Once localized to this structure, oviductin molecules would act as a protective shield around the oocyte and early embryo by virtue of their densely glycosylated mucin-type domains.

Epidermal growth factor stimulates hydrolysis of phosphatidylinositol 4,5-bisphosphate, generation of diacylglycerol and exocytosis in mouse spermatozoa

Mouse spermatozoa stimulated with epidermal growth factor (EGF) or zona pellucida (ZP) experienced phosphatidylinositol 4,5-bisphosphate hydrolysis, diacylglycerol (DAG) generation and acrosomal exocytosis. The agonists showed additive effects but the action of EGF is likely to be mediated by a distinct receptor because maximal stimulation achieved with EGF was enhanced further by ZP. Generation of DAG and exocytosis stimulated by EGF were inhibited by tyrphostin A48, indicating that tyrosine kinase activity mediates EGF action. On the other hand, pertussis toxin did not affect the EGF-induced formation of DAG or exocytosis, ruling out the involvement of sperm Gi-like proteins. These results indicate that EGF could be an important co-factor in the initiation of exocytosis in spermatozoa.