Effects of laminin-treated membrane culture inserts on the growth of bovine oocyte–granulosa cell complexes collected from early antral follicles

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Growing bovine oocytes represent a potential source of embryos, but this has not been adopted in practice. Although several offspring were produced following a two-week culture period, further optimization of the culture system is required. In vivo, the outermost granulosa cell layer is in direct contact with the basement membrane (BM); however, this interaction is absent in cultured oocyte–granulosa cell complexes (OGCs). Since the BM is known to have regulatory roles, this study examined the effects of BM components on oocyte growth by treating membrane inserts with laminin, a major BM constituent, or with the laminin-containing protein mixture Matrigel^®. OGCs containing growing oocytes (90–106 μm in diameter) were cultured from Day 0 to Day 14 on plain membranes or on membranes with spots of Matrigel or laminin. A modified minimum essential medium α supplemented with 5% fetal bovine serum, 4% polyvinylpyrrolidone (average molecular weight, 360,000), steroid hormones, and 3 mM hypoxanthine was used. Granulosa cell migration was more pronounced in the treated spots, particularly in the Matrigel-treated group where migration extended across the entire treated area. Oocyte volume increased to 147% in the control group, 158% in the Matrigel group, and 160% in the laminin group, with Day 1 values normalized to 100%. Oocytes cultured on laminin-treated membranes were significantly larger than those in the control group (P < 0.05). Following in vitro fertilization, approximately 5% of the oocytes in each group developed to the blastocyst stage. Overall, the interaction between granulosa cells and laminin-treated membranes positively influenced the growth of bovine oocytes in vitro.