Despite its functional significance in mammals and birds, the biological role of gonadotropin-inhibitory hormone (GnIH) in reproduction is still far from being fully understood in teleosts. In the current study, we have identified LPXRFa, the piscine ortholog of GnIH, and its cognate receptor (LPXRFa-R) in yellowtail kingfish (YTK), which is considered as a promising species for aquaculture industry worldwide. The YTK cDNA sequence of lpxrfa was 534 base pair (bp) in length and encoded a 178-amino acids (aa) preprohormone. The LPXRFa precursor comprised three putative peptide sequences that included –MPMRF, –MPQRF, or -LPERL motifs at the C-termini, respectively. The YTK lpxrfa-r cDNA sequence was composed of 1265 bp that gave rise to a LPXRFa-R of 420 aa, encompassing the characteristic seven hydrophobic transmembrane domains. In males, both lpxrfa and lpxrfa-r transcripts could be detected at high levels in the brain and testis. In females, a noteworthy expression of lpxrfa was observed in the brain and ovary, while the expression of lpxrfa-r was especially evident only in the brain. To study the ontogeny of LPXRFa system, transcript levels were also investigated during early life stages. Variable expression of the LPXRFa system was observed during all stages of YTK embryogenesis. The highest expression of lpxrfa and lpxrfa-r were noticed at 7 dph and 15 dph, respectively. Furthermore, LPXRFa peptides stimulated growth hormone (gh), luteinizing hormone (lhβ) and follicle-stimulating hormone (fshβ) gene expression from the pituitary. Taken together, our results provide initial evidence for the existence of the LPXRFa system in yellowtail kingfish and suggest its possible involvement at early development and reproductive functions.

尽管在哺乳动物和鸟类中具有重要的功能，但促性腺激素抑制激素 (GnIH) 在繁殖中的生物学作用仍远未在硬骨鱼中得到充分了解。在目前的研究中，我们在黄尾王鱼 (YTK) 中鉴定了 GnIH 的鱼直系同源物 LPXRFa 及其同源受体 (LPXRFa-R)，被认为是全球水产养殖业的一个有前途的物种。lpxrfa的YTK cDNA序列长度为534个碱基对（bp），编码一个178个氨基酸（aa）的前激素原。LPXRFa 前体包含三个推定的肽序列，分别包括 C 端的 -MPMRF、-MPQRF 或 -LPERL 基序。YTK lpxrfa-rcDNA 序列由 1265 bp 组成，产生 420 aa 的 LPXRFa-R，包括特征性的七个疏水跨膜结构域。在男性中，可以在大脑和睾丸中检测到高水平的lpxrfa和lpxrfa-r转录物。在女性中，lpxrfa的显着表达在大脑和卵巢中观察到，而lpxrfa-r的表达仅在大脑中特别明显。为了研究 LPXRFa 系统的个体发育，还研究了早期生命阶段的转录水平。在 YTK 胚胎发生的所有阶段都观察到 LPXRFa 系统的可变表达。lpxrfa和lpxrfa-r的最高表达分别在 7 dph 和 15 dph 时注意到。此外，LPXRFa 肽刺激垂体的生长激素 ( gh )、黄体生成素 ( lhβ ) 和卵泡刺激素 ( fshβ ) 基因表达。总之，我们的研究结果为黄尾王鱼中 LPXRFa 系统的存在提供了初步证据，并表明它可能参与早期发育和生殖功能。