In vitro and in vivo association of an oviduct estrus-associated protein with bovine zona pellucida.

The interaction between the bovine egg zona pellucida and a 97 kDa estrus-associated protein produced by the oviduct was examined in vitro and in vivo. In vitro matured bovine eggs were incubated with oviduct fluid recovered throughout the estrous cycle from separate indwelling cannulae placed in the ampulla and isthmus of the same oviduct. Immunofluorescence techniques and a polyclonal antiserum against the 97 kDa protein were used to localize this protein on washed eggs previously incubated with oviduct fluid. Intensity and distribution of immunofluorescence varied with stage of cycle and to a lesser degree with region of oviduct from which the oviduct fluid was obtained. The most intense fluorescence was observed on the zonae pellucidae of eggs incubated with oviduct fluid pooled from days near estrus and ovulation compared to fluid pooled from luteal stage days. The immunofluorescence of isthmus-derived oviduct fluid was more intense than was ampulla-derived oviduct fluid collected near estrus. The zonae pellucidae of 7-day-old embryos flushed from the uterus displayed immunofluorescence comparable to that observed on the zonae pellucidae of eggs incubated in vitro with peri-estrus oviduct fluid. No immunofluorescence was observed associated with the perivitelline space, egg cytoplasm, or blastomeres. The apparent uptake of a 97 kDa estrus-associated protein by the zonae pellucidae of eggs in vitro and embryos in vivo may indicate that this protein functions in fertilization and/or early embryo development.