Reproduction Abstracts

Introduction: A high concentration of polyvinylpyrrolidone (PVP, average molecular weight 360 000) supplementation in culture medium exerts a positive influence on the growth and morphological organization of bovine oocyte–cumulus/granulosa cell complexes in a long-term culture. The objective of the present study was to determine the effect of PVP supplementation on the number of transzonal projections (TZPs) traversing the zona pellucida from cumulus cells to the oocyte.

Materials and methods: Bovine oocyte–granulosa cell complexes with a mean oocyte diameter of ~ 100 μm were cultured on membrane inserts for 14 days, with culture medium that was supplemented with or without 4% PVP (w/v). After the 14-day culture period, the oocytes enclosed with cumulus cells were collected and fixed for immunofluorescence microscopy. F-actin of these cells was labelled with Alexa Fluor 488 phalloidin and visualized using a confocal laser-scanning microscope.

Results and discussion: Although numerous TZPs were observed irrespective of the presence or absence of PVP, there were significantly more TZPs after growth in medium with PVP than in control medium, as indicated by image analysis using ImageJ. This observation suggests that promoting effects of PVP supplementation on oocyte growth may involve modulation of connectivity between oocytes and their companion granulosa cells.