Differential expression of focimatrix and steroidogenic enzymes before size deviation during waves of follicular development in bovine ovarian follicles

Abstract

During the growth of bovine follicles, one emerges from a wave as the largest and dominant follicle. What regulates dominance is not known but candidates include oestradiol, transforming growth factor beta β1 (TGFB1), and recently CYP11AI (cholesterol side-chain cleavage) and focal intra-epithelial matrix (focimatrix). To examine this, pairs of bovine ovaries with 2 or more follicles of equal size (>5 mm) and hence in a wave before deviation, were collected at an abattoir (6.7 ± SEM 0.1 mm diameter; n = 14 animals, 35 follicles in total). These follicles were dissected and follicular fluid collected to measure progesterone and oestradiol concentrations. A portion of the follicle wall was processed for histological classification of health or atresia and granulosa cells were harvested for quantitative RT-PCR of focimatrix components [COL4A1 (collagen type IV α1), LAMB2 (laminin β2) and HSPG2 (perlecan)], steroidogenic enzymes [CYP11A1 and CYP19A1] and TGFB1. For statistical analyses follicles within each animal were grouped into either the highest (oestradiol, CYP11A1) or lowest (TGFB1) expression (n = 14) for comparison with the remaining follicles (n = 21). When grouped on oestradiol no other parameters differed significantly, and when grouped on TGFB1 some parameters were different however the levels were also lower, and not higher as expected. When grouped on CYP11A1 other parameters were significantly elevated in the high CYP11A1 group (COL4A1P < 0.05; LAMB2P < 0.01; HSPG2P < 0.01 and CYP19A1P < 0.001). This suggests that steroidogenesis and focimatrix might be important in a follicle attaining dominance.