Physiology and Endocrinology Symposium: Regulation of the Growing Follicle Pool – Basic and Applied Aspects
By: Lauren Soranno
The Physiology and Endocrinology Symposium held on Wednesday, July 11th at the ASAS-CSAS Annual Meeting focused on the regulation of the growing follicle pool. Follicular development was analyzed in sheep, dairy cows, and pigs. While a few of the speakers discussed more about the process of follicular development, a majority gave a simple background on the process and went more in depth suggesting factors that regulate follicular growth. Dr. Danielle Monniaux, a researcher at the University of Tours, began the presentations by discussing possible regulations of early follicular development in sheep. She explained how a balance between stimulating (KITLG/PI3K, JNK) and inhibiting pathways (AMH/SMAD) determines the primordial to primary follicle transition. Dr. Monniaux analyzed a FecB mutation concluding that the mutation slows down the activation processes and the initiation of granulosa cell proliferation after activation. Molecular oocyte-granulosa cell dialog involving gap junctions, cytokines, and growth factors helps to drive follicular development and abnormal expression levels of these factors can disrupt the development causing female sterility or advance follicular maturation causing increased female fertility. Dr. Monniaux stressed the importance of developing a better knowledge of cell interactions during follicular development to potentially improve biotechnology methods of fertility preservation. Dr. James J. Ireland, a professor at Michigan State University, analyzed the relationship between the size of ovarian reserves, ovarian function, fertility, and anti-mullerian hormone (AMH) in dairy cows. He believed that AMH is predicative of reproductive performance, milk production, and longevity in cattle and that the number of healthy follicles is positively correlated with ovarian function and fertility. Ireland showed data that suggested as AMH increased, the size of the ovary as well as the follicles increased and cattle with lower AMH concentrations were culled more compared with cattle that had high AMH concentrations due to poor reproductive function. He concluded that genetic/environmental manipulations of AMH can increase the size of ovarian reserves and ovarian function, which can lead to improved fertility and longevity.
Next, Dr. Holly A. LaVoie, a professor at the University of South Carolina School of Medicine, explained the physiological regulation of ovarian follicle growth in depth, but stressed that more work still needs to be done to get more information on the regulation and development of follicles in pigs. Dr. LaVoie went into detail about the roles of follicle stimulating hormone (FSH) and luteinizing hormone (LH) during follicular development specifically in relation to granulosa cells, antral follicles, and induction of final maturation and ovulation. Overall, follicular development during the pig estrous cycle requires primordial follicle activation, changes in FSH/LH receptors and concentrations, and steroidogenic proteins. Dr. Robert V. Knox, an associate professor at the University of Illinois, ended the symposium by discussing factors that influence follicular development in gilts and sows. He explained that boar exposure, increased dietary energy, and transportation are all factors that can induce follicle development, while poor body condition, parity, heat stress, and negative energy balance can inhibit follicle growth. By better understanding the activators and inhibitors of follicular development, fertility and longevity can potentially be increased. Overall, ovarian follicles of various species have different, yet similar development processes. All of the processes are regulated by internal and external factors such as AMH, signaling pathways, heat stress, and inadequate feed/growth, that can impact the size of the follicles as well as ovulation, which will in turn impact fertility and longevity. Learning more about the activators and inhibitors present in the development of follicular development will be important to increase fertility and health.