Focimatrix Gene Expression in Bovine Pre- and Post-Deviated Follicles.

Abstract

The growth of bovine antral follicle >5 mm occurs in 2 or 3 waves within a cycle. From each follicular wave one follicle emerges as the largest and hence dominant follicle. As follicles increase in size, concentrations of oestradiol in follicular fluid and expression of steroidogenic enzymes and focal intra-epithelial matrix (focimatrix) increase. Furthermore, studies have suggested that transforming growth factor beta 1 (TGFB1) is reduced in the future dominant follicle during selection. We hypothesised that focimatrix may also be involved in the selection process. To examine this, bovine ovaries were collected at an abattoir and two to four of the largest follicles were individually dissected and follicular fluid was collected. A 1 x 3 mm section of the follicle wall was processed for histological classification of health or atretia, and granulosa cells harvested for quantitative RT-PCR. Follicles were classified as pre-deviated if the largest two or more healthy follicles were of equal size [6.7 ± 0.1 mm (mean + SEM); n = 14 animals, 35 follicles in total] and deviated if they differed in size by 0.5-1.0 mm (7.2 ± 0.2 mm; n = 11 animals, 26 follicles in total). Messenger RNA levels of genes for focimatrix components [COL4A1 (collagen type IV alpha1), LAMB2 (laminin beta2) and HSPG2 (perlecan)], steroidogenic enzymes (CYP11A1 and CYP19A1) and TGFB1 were determined. For analyses, pre-deviated follicles were respectively grouped into high (n = 14) and low COL4A1 levels of expression (n = 21), while deviated follicles were classified into dominant (n = 12) and subordinate (n = 14) based on diameter. High COL4A1 follicles expressed significantly higher COL4A1 as expected as well as higher HSPG2 compared to low COL4A1 follicles (P < 0.05, independent samples t-test). Dominant follicles did not differ from subordinate follicles in terms of gene expression. Dominant follicles were significantly larger than subordinate or pre-deviated follicles (P < 0.01, ANOVA, SNK-post hoc test). COL4A1 and HSPG2 were significantly higher in high COL4A1 pre-deviated follicles than deviated follicles (P < 0.05, ANOVA, SNK-post hoc test). LAMB2 was significantly higher in high COL4A1 than dominant follicles (P < 0.05), but was not significantly different from low COL4A1 pre-deviated follicles or subordinate follicles. CYP11A1, CYP19A1 and TGFB1 were not differentially expressed before or after deviation. Thus focimatrix is expressed during follicle selection and may play a role in follicular dominance. (poster)