Evol Ecol Res 20: 317-329 (2019)     Full PDF if your library subscribes.

Changes in kisspeptin, GnRH, and gonadotropin mRNA levels in male Threespine stickleback (Gasterosteus aculeatus) during photoperiod-induced sexual maturation

Yi Ta Shao1,2, Chrysoula Roufidou3, Pei Chi Chung1 and Bertil Borg3

1Institute of Marine Biology, National Taiwan Ocean University, Keelung, Taiwan, 2Center of Excellence for the Oceans, National Taiwan Ocean University, Keelung, Taiwan and 3Department of Zoology, Stockholm University, Stockholm, Sweden

Correspondence: Y.T. Shao, Institute of Marine Biology, National Taiwan Ocean University, Keelung 20224, Taiwan. email: itshao@mail.ntou.edu.tw


Background: Both gonadotropin-releasing hormone (GnRH) and kisspeptin have a critical role in the photoperiodic control of sexual maturation in mammals.

Question: What are the roles of GnRH and kisspeptin in the photoperiodic control of sexual maturation in the Threespine stickleback, Gasterosteus aculeatus?

Method: If kisspeptin and GnRH trigger the photoperiodic induction of maturation in fishes, they would be expected to be activated prior to, or at least no later than, the gonadotropins. The mRNA levels of brain gnrh2, gnrh3, kiss2 and its receptor, gpr54, as well as of pituitary lh-β and fsh-β, were measured in males under standard laboratory conditions [16 hours light/8 hours dark (L16/D8) or 8 hours light/16 hours dark (L8/D16)] after 3, 10, 19, and 29 days at 20°C.

Results: From day 19, males in the long-day photoperiod (L16/D8) condition were visibly mature with bright breeding coloration. Compared with short-day photoperiod (L8/D16) fish, L16/D8 fish had higher lh-β mRNA levels at days 10, 19, and 29, and higher fsh-β mRNA levels at day 10 only. Furthermore, L16/D8 fish had higher gnrh3 mRNA levels at days 10 and 29, and higher gnrh2 mRNA levels at day 29, than L8/D16 fish. Finally, kiss2 and gpr54 mRNA levels of L16/D8 fish were significantly higher than those of L8/D16 fish at days 19 and 29, respectively.

Conclusions: At the onset of sexual maturation, the levels of lh-β, fsh-β, and gnrh3 rose earlier than those of kiss2 and gpr54. These results are consistent with GnRH3 having a role in the early phases of maturation, but do not support a role for kisspeptin in photoperiodic initiation of maturation in male stickleback.

Keywords: fsh-β, lh-β, gnrh2, gnrh3, gpr54, kiss2, reproduction, stickleback, teleosts.

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