Gene expression in bovine ovarian follicle granulosa. Bos taurus

Granulosa cells mature and die as ovarian follicles enlarge and die (undergo atresia) under the influence of hormones and intrafollicular factors. Later in follicular development, a fluid-filled antrum is formed, a process which is accompanied by a high rate of atresia. These small antral follicles (5 mm or less in diameter in the cow) contain granulosa of 2 different phenotypes, rounded or columnar, whereas follicles larger than 5 mm have the rounded phenotype only. Prior to ovulation, in larger follicles greater than 10 mm in size, the granulosa begin to migrate and differentiate in preparation for oocyte release and formation of the corpus luteum. These two key phases of follicular development were studied by gene expression microarray analysis using a bovine model to dissect the molecular mechanisms underlying these processes. Overall design: Four groups of bovine ovarian follicles were selected for analysis. Follicle size, type and array number for each group are as follows: small (3-5 mm) healthy rounded (n=5), small healthy columnar (n=5), atretic (n=5) and large healthy (>10 mm; n=4). For each group, the RNA from a single follicle was used to hybridise an array, except for 3 small healthy samples which were pooled from 2 follicles each due to low RNA.