Increased expression of kisspeptin and GnRH forms in the brain of scombroid fish during final ovarian maturation and ovulation

• Main Authors: Selvaraj Sethu, Kitano Hajime, Amano Masafumi, Ohga Hirofumi, Yoneda Michio, Yamaguchi Akihiko, Shimizu Akio, Matsuyama Michiya
• Format: Article
• Language: English
• Published: BMC 2012-08-01
• Series: Reproductive Biology and Endocrinology
• Subjects: Kisspeptins; Kiss; GnRH; Mackerel; Brain; Pituitary; Spawning cycle
• Online Access: http://www.rbej.com/content/10/1/64

<p>Abstract</p> <p>Background</p> <p>Kisspeptins (Kiss) are prime players in the control of reproductive function through their regulation of gonadotropin-releasing hormone (GnRH) expression in the brain. The experimental scombroid fish, chub mackerel (<it>Scomber japonicus</it>) expresses two <it>kiss</it> (<it>kiss1</it> and <it>kiss2</it>) and three <it>gnrh</it> (<it>gnrh1</it>, <it>gnrh2</it>, and <it>gnrh3</it>) forms in the brain. In the present study, we analyzed expression changes of <it>kiss</it> and <it>gnrh</it> mRNAs in the brain and corresponding GnRH peptides in the brain and pituitary during final ovarian maturation (FOM) and ovulation.</p> <p>Methods</p> <p>Female fish possessing late vitellogenic oocytes were injected with GnRH analogue to induce FOM and ovulation. Fish were observed for daily spawning activities and sampled one week post-injection at germinal vesicle migration (GVM), oocyte hydration, ovulation, and post-ovulatory time periods. Changes in relative mRNA levels of <it>kiss</it> and <it>gnrh</it> forms in the brain were determined using quantitative real-time PCR. Changes in GnRH peptides in the brain and pituitary were analyzed using time-resolved fluoroimmunoassay.</p> <p>Results</p> <p>Both <it>kiss1</it> and <it>kiss2</it> mRNA levels in the brain were low at late vitellogenic stage and increased significantly during the GVM period. However, <it>kiss1</it> mRNA levels decreased during oocyte hydration before increasing again at ovulatory and post-ovulatory periods. In contrast, <it>kiss2</it> mRNA levels decreased at ovulatory and post-ovulatory periods. Levels of <it>gnrh1</it> mRNA in the brain increased only during post-ovulatory period. However, levels of <it>gnrh2</it> and <it>gnrh3</it> mRNAs were elevated during GVM and then, decreased during oocyte hydration before increasing again at ovulatory period. During post-ovulatory period, both <it>gnrh2</it> and <it>gnrh3</it> mRNA levels declined. Peptide levels of all three GnRH forms in the brain were elevated during GVM and oocyte hydration; their levels were significantly lower during late vitellogenic, ovulatory, and post-ovulatory periods. In contrast, pituitary GnRH peptide levels did not show any significant fluctuations, with the GnRH1 peptide levels being many-fold higher than the GnRH2 and GnRH3 forms.</p> <p>Conclusion</p> <p>The results indicate increased expression of multiple Kiss and GnRH forms in the brain and suggest their possible involvement in the regulation of FOM and ovulation in captive female chub mackerel.</p>