Kisspeptin is an endogenous ligand that modulates gonadotropin-releasing hormone (GnRH) secretion and plays an essential role in the reproduction of mammals. In fish, two subtypes of kiss genes (kiss1 and kiss2), which encode kisspeptins, have been reported. Our previous study showed that kisspeptin 2 receptor (KissR2) is highly expressed in the vicinity of GnRH1 neurons, and that centrally administered Kiss2, but not Kiss1, significantly increased gonadotropin synthesis in chub mackerel Scomber japonicus. The results of this latter study suggested that the kisspeptin system plays an important role in chub mackerel reproduction, and that Kiss2 in particular plays a dominant role in the regulation of the central reproductive axis. In the present study, we identified the functional form of Kiss2 peptide in 16 species of Scombridae. All the species possessed kiss2, and the deduced mature peptide had 12 amino acids, all of which were very highly conserved, except for the second amino acid from the N-terminal end that was found to vary across species. However, species specificity of the second residue did not affect signal transduction in chub mackerel KissR2, bluefin tuna Thunnus orientalis KissR2, or Japanese Spanish mackerel Scomberomorus niphonius KissR2. Therefore, the importance of the Kiss2 system, shown in studies of chub mackerel reproduction, may be relevant across all species of Scombridae.

中文翻译：

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16 种鲭科中kisspeptin 2 十二肽的分子特征

Kisspeptin 是一种内源性配体，可调节促性腺激素释放激素 (GnRH) 的分泌，并在哺乳动物的繁殖中发挥重要作用。在鱼中，已经报道了编码kisspeptins 的两种kiss 基因亚型（kiss1 和kiss2）。我们之前的研究表明，kisspeptin 2 受体 (KissR2) 在 GnRH1 神经元附近高度表达，并且中枢给药的 Kiss2 而不是 Kiss1，显着增加了鲭鱼 Scomber japonicus 的促性腺激素合成。后一项研究的结果表明，kisspeptin 系统在鲭鱼繁殖中起着重要作用，尤其是 Kiss2 在中央繁殖轴的调节中起主导作用。在本研究中，我们确定了 16 种鲭科中 Kiss2 肽的功能形式。所有物种都拥有kiss2，推导出的成熟肽有12个氨基酸，除了N末端的第二个氨基酸因物种而异外，所有氨基酸都非常保守。然而，第二个残基的物种特异性不影响鲭鱼 KissR2、蓝鳍金枪鱼 Thunnus orientalis KissR2 或日本鲭鱼 Scomberomorus niphonius KissR2 的信号转导。因此，鲭鱼繁殖研究中显示的 Kiss2 系统的重要性可能与鲭科的所有物种有关。第二个残基的物种特异性不影响鲭鱼 KissR2、蓝鳍金枪鱼 Thunnus orientalis KissR2 或日本鲭鱼 Scomberomorus niphonius KissR2 中的信号转导。因此，鲭鱼繁殖研究中显示的 Kiss2 系统的重要性可能与鲭科的所有物种有关。第二个残基的物种特异性不影响鲭鱼 KissR2、蓝鳍金枪鱼 Thunnus orientalis KissR2 或日本鲭鱼 Scomberomorus niphonius KissR2 中的信号转导。因此，鲭鱼繁殖研究中显示的 Kiss2 系统的重要性可能与鲭科的所有物种有关。