534. CO-ORDINATED GENE EXPRESSION IN BOVINE GRANULOSA CELLS PRECEDES FOLLICULAR DOMINANCE

Abstract

During growth of bovine follicles, one emerges as the largest and dominant follicle. What regulates dominance remains unknown, but candidates include oestradiol, TGFB1, and recently CYP11A1 and focal intra-epithelial matrix (focimatrix). The two to four largest follicles were dissected from pairs of bovine ovaries and follicular fluid collected. A portion of the follicle wall was histologically classified for follicle health or atretia, and granulosa cells harvested for quantitative RT-PCR. Messenger RNA levels of focimatrix (COL4A1, LAMB2, HSPG2), steroidogenic enzymes (CYP11A1, CYP19A1) and TGFB1 genes were measured. Follicular fluid progesterone and oestradiol concentrations were measured by RIA. Follicles were identified as pre-deviated (before size-deviation) if the largest two or more healthy follicles were of equal size (6.7±0.1 mm, n = 14 animals, 35 follicles), and as post-deviated (after size-deviation) if they differed in size by 0.5–1.0 mm (7.2±0.2 mm; n = 11 animals, 26 follicles). For analyses, pre-deviated follicles were grouped into either the highest (oestradiol, CYP11A1) or lowest (TGFB1) expression (n = 14) and compared to the remaining follicles (n = 21). Deviated follicles were classified into dominant (n = 12) and subordinate (n = 14) based on diameter. Dominant follicles did not differ from subordinate follicles in any parameters measured, but were significantly larger than subordinate or pre-deviated follicles (P<0.01). For pre-deviated follicles grouped on oestradiol no parameters differed significantly, and when grouped on TGFB1, LAMB2 (P<0.05), HSPG (P<0.05), CYP19A1 (P<0.05) and TGFB1 (P<0.01) differed but levels were lower, not higher as expected. When grouped on CYP11A1, COL4A1 (P<0.05), LAMB2 (P<0.01), HSPG2 (P<0.01) and CYP19A1 (P<0.001) were significantly elevated in the high CYP11A1 group. This suggests that CYP11A1 and focimatrix might be important in follicle dominance.