Ovulation, which is induced by the ovulatory luteinizing hormone (LH) surge in vertebrates, is a dynamic process that results in a discharge of one or more fertilizable oocytes from the ovarian follicle into the ovarian cavity or into the abdominal cavity. Follicle rupture is a core event of the ovulatory process and has been the subject of intensive investigation. Prostaglandins are well known to be central regulators of vertebrate ovulation. Studies addressing the role of prostaglandins in mammalian ovulation have established that they are involved in the processes of oocyte maturation and cumulus oocyte complex expansion. In contrast, despite the first indication of the role of prostaglandins in teleost ovulation appearing 40 years ago, the mechanistic background of their role has long been unknown. However, studies conducted on the teleost medaka over the past decade have provided valuable information. Emerging evidence indicates a critical role of prostaglandin E2 and its receptor subtype Ptger4b in the process of follicle rupture. In addition, our studies have revealed that activation of the melatonin/melatonin receptor system in the ovulating follicle is required for the prostaglandin E2-mediated follicle rupture process. In this talk, we summarize studies addressing the role of prostaglandins in teleost ovulation and describe recent advances. To help understand differences from and similarities to ovulation in mammalian species, the findings on the roles of prostaglandins in mammalian ovulation are discussed in parallel.

*Takayuki Takahashi, Ph.D., Emeritus Professor of Hokkaido University, Japan
1979 Ph.D. in Zoology (Hokkaido University)
1980-1986 Research Associate, Protein Studies Lab at Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, USA
1987-1993 Assistant Professor, Faculty of Science, University of Tokyo, Japan
1993-2016 Professor, Faculty of Science, Hokkaido University, Japan
2016-2019 Research Professor, Hokkaido University, Japan
Research interests
My research activities are in the field of reproductive biology of vertebrates including fish. In particular, my laboratory has been closely associated with ovulation studies using a teleost medaka by cellular and molecular biological approaches. Our final goal is to get insights into the evolutional aspect of ovulation in the animal kingdom.
We were the first to report that, using the teleost medaka, (i) MMPs and plasminogen activator/plasmin are involved in follicle rupture during ovulation (PNAS, 2005; Biol. Reprod., 2012, 2015). In addition, our studies showed that (ii) many ovulation-related-genes are induced by the surge of LH at ovulation (PLoS ONE, 2013; Biol. Reprod., 2014; MCE, 2017), (iii) activation of the prostaglandin E2 and the receptor system is required for follicle rupture (MCE, 2011, 2012, 2017; Biol. Reprod., 2016), and (iv) follicle rupture during ovulation is the process which proceeds under precise endocrine control (MCE, 2017; Reproduction, 2019; cells, 2019).
In 2010, Prize from the Zoological Society of Japan
“Discovery of ovulatory proteases and elucidation of follicle rupture mechanism in teleost medaka”