AUTHOR=Zhao Chunyan , Wang Bin , Liu Yifan , Feng Chengcheng , Xu Shihong , Wang Wenqi , Liu Qinghua , Li Jun 

TITLE=New Evidence for the Existence of Two Kiss/Kissr Systems in a Flatfish Species, the Turbot (Scophthalmus maximus), and Stimulatory Effects on Gonadotropin Gene Expression

JOURNAL=Frontiers in Endocrinology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2022.883608

DOI=10.3389/fendo.2022.883608

ISSN=1664-2392

ABSTRACT=<p>Seasonal reproduction is generally controlled by the hypothalamus-pituitary-gonadal (HPG) axis in fish. Previous studies have demonstrated that the kisspeptin (Kiss)/kisspeptin receptor (Kissr) system, a positive regulator of the HPG axis, mediates the responses to environmental cues. Turbot (<italic>Scophthalmus maximus</italic>), a representative species of Pleuronectiformes, is one of the most commercially important fish species cultured in Europe and North China. However, the mechanisms by which the Kiss/Kissr system regulates the reproductive axis of turbot according to seasonal changes, especially photoperiod, have not been clearly characterized. In the current study, the cDNA sequences of <italic>kiss2</italic>/<italic>kissr2</italic>, along with <italic>kiss1</italic>/<italic>kissr3</italic> which was thought to be lost in flatfish species, were cloned and functionally characterized. The <italic>kiss1</italic>, <italic>kiss2</italic>, and <italic>kissr3</italic> transcripts were highly detected in the brain and gonad, while <italic>kissr2</italic> mRNA was only abundantly expressed in the brain. Moreover, <italic>kiss</italic>/<italic>kissr</italic> mRNAs were further examined in various brain areas of both sexes. The <italic>kiss1</italic>, <italic>kissr2</italic>, <italic>kissr3</italic> mRNAs were highly expressed in the mesencephalon, while a substantial degree of <italic>kiss2</italic> transcripts were observed in the hypothalamus. During annual reproductive cycle, both <italic>kiss</italic> and <italic>kissr</italic> transcript levels declined significantly from the immature to mature stages and increased at the degeneration stage in the brains of both sexes, especially in the mesencephalon and hypothalamus. The ovarian <italic>kiss1</italic>, <italic>kiss2</italic>, and <italic>kissr2</italic> mRNA levels were highest at the vitellogenic stage (mature stage), while expression of <italic>kissr3</italic> was highest at the immature stage. The testicular <italic>kiss</italic> and <italic>kissr</italic> transcripts were highest in the immature and degeneration stages, and lowest at the mature stage. In addition, intraperitoneal injection of Kiss1-10 and Kiss2-10 significantly stimulated mRNA levels of pituitary <italic>lhβ</italic>, <italic>fhsβ</italic>, and <italic>gthα</italic>. In summary, two Kiss/Kissr systems were firstly proven in a flatfish species of turbot, and it has a positive involvement in controlling the reproduction of the Kiss/Kissr system in turbot. The results will provide preliminary information regarding how the Kiss/Kissr system controls seasonal reproduction in turbot broodstock.</p>