RNA-seq profiling of theca and granulosa tissue of dominant follicle at 3 stages of follicular development in cows and heifers.

Cellular mechanisms that contribute to low estradiol concentrations produced by the preovulatory ovarian follicle in cattle with a compromised metabolic status (such as lactatino) are largely unknown. To gain insight into the main metabolic mechanisms affecting preovulatory follicle function RNAseq profiling was conducted on non-lactating Holstein-Friesian heifers (n=16) and lactating Holstein-Friesian cows (n=17) at three stages of preovulatory follicle development: A) newly selected dominant follicle in the luteal phase (Selection); B) follicular phase before the LH surge (Differentiation) and C) pre-ovulatory phase after the LH surge (Luteinization). Based on a combination of RNA sequencing, ingenuity pathway analysis and Q-RT-PCR validation several important molecular markers involved in steroid biosynthesis, such as the expression of steroidogenic acute regulatory protein (STAR) within developing dominant follicles, were identified to be affected (downregulated) by the catabolic state. We propose that the adverse metabolic environment caused by lactation decreases preovulatory follicle function by affecting cholesterol transport into the mitochondria to initiate steroidogenesis. Overall design: Granulosa and Theca samples from the dominant follicle were taken from cows and heifers at stages: selection, differentiation and luteinization.