IDENTIFICATION OF A SPERM PENETRATION FACTOR IN THE OVIDUCT OF THE GOLDEN-HAMSTER

Previously, we found oviductal eggs to be significantly more penetrable and fertilizable in vitro than ovulated eggs collected from the ovarian bursa, while bursal eggs were comparable to mature (unovulated) follicular eggs. Incubation of follicular eggs with a soluble eluate of oviductal egg cumulus complexes (COF) increased sperm penetration: the activity was macromolecular, was destroyed at 56 degrees C, and was produced in the oviduct. We now report purification of this oviductal factor that enhances penetration of follicular eggs and have identified it as oviductin (OVN). Oviducts, 1-1.5 h post-LH from eCG-primed females, were homogenized and the cytosolic fraction was chromatographed on a Helix pomatia lectin affinity column; specific proteins were eluted with 0.2 M N-acetyl-D-gatactosamine. Fractions were monitored by dot-blot assay using as the primary antibody monoclonal antibody (mAb) 1C4 against OVN. Proteins were resolved by one-dimensional SDS-gel electrophoresis, followed by electrotransfer and immunostaining of Western blots. OVN fractions were indexed to COF by quantitative dot-blot assay, and activity was bioassayed by penetration of follicular eggs within 1 h of coincubation with precapacitated sperm +/- factors: COF and BSA (high and low controls, respectively) and fractions from the lectin-isolated peak. The mean penetration rates for three isolations were 17 +/- 4.0(a), 51.7 +/- 5.0(b), and 43 +/- 2.7(b)% for BSA, COF, and column fractions, respectively (p less than or equal to 0.05). Purified OVN bound to follicular zonae during culture. Acrosome-intact sperm heads bound OVN during 30 min of incubation both before (t = 0 h) and after capacitation (t = 5.5 h) (visualized by indirect immunofluorescence). We conclude that OVN enhances penetration and fertilization by altering both sperm and eggs.