Genome-Wide Gene Expression Profiling of Bovine Follicles: Identification of Genes Involved in the Growth of Dominant Follicles by Microarray Analysis.

In monovular species including cattle, usually one follicle is selected and continues growing to become dominant during the follicular wave. Although the dominant follicle acquires ovulatory capacity, if it fails to ovulate, the follicle undergoes atresia and new follicular wave emerges. It is well documented that hormonal milieu plays critical role in the fate of the dominant follicle. In addition, it seems that the growth and atresia of dominant follicle is regulated by specific changes of numerous genes expressed in follicular cells. In this study, we tried to identify genes differentially expressed during growth and atresia of dominant follicle using microarray analysis. Paired ovaries were obtained from five Japanese-black cows and five follicles (≥8 mm in diameter) were dissected. Total RNA was extracted from individual follicles and used for microarray analysis. Sixty-mer nucleotides probes for customized microarray were synthesized on the glass slide. Array fabrication was carried out by the Agilent Technologies. The annotated bovine oligonucleotide array represented 10263 sequences. Of which, 4466 genes were known bovine genes, 5697 unknown sequences were possible candidates for novel bovine genes, and 100 internal references. The expression levels of 78 genes were found to be enhanced exceeding twenty-fold among the follicles. Follicles were classified into two groups (Group 1 and Group 2) by hierarchical cluster analysis. Group 1 follicles were characterized by higher expression of 46 genes including FSHR, CYP19 and inhibin α subunit. Whereas other 32 genes including IGFBP5, TIMP1 and uPA, were predominately expressed in Group 2 follicles. Therefore, follicles in Group 1 and 2 were considered to be growing and atretic follicles, respectively. Expression profiles of representative 19 genes (9 genes highly expressed in Group 1 and 10 genes highly expressed in Group 2) were confirmed by using quantitative RT-PCR. In summary, we analyzed genome-wide transcriptome profiles of dominant follicles in cows by using customized oligonucleotide array. Results in the present study suggested that gene expression profiles of dominant follicles were classified into 2 groups representing the status of follicular development. Expression of stage-specific genes in dominant follicles may be closely associated with its growth or atresia. Several genes identified in this study will provide intriguing candidates for the determinant of follicular growth. This study was supported by JSPS Research Fellowships for Young Scientists.