Roles of the LH–LHR1/2 System in Ovarian Maturation of Spotted Scat (Scatophagus argus)

Luteinizing hormone receptors (LHRs) play important roles in teleost ovarian development and oocyte maturation. In this study, two LHR paralogues, lhr1 and lhr2, were cloned and characterized in spotted scat (Scatophagus argus). Their open reading frames were 2169 and 2022 bp in length and encoded proteins of 722 and 673 amino acids, respectively. Both genes showed relatively high expression along the hypothalamic–pituitary–gonadal axis and increased markedly during late ovarian development, reaching their highest expression levels at stage IV. In cultured ovarian tissue, hCG rapidly induced the expression of steroidogenesis- and maturation-associated genes. Blockade of either LHR1 or LHR2 attenuated hCG-induced expression of hsd3b7, p450c17a, cdc2, and 20β-hsd. Both receptor antibodies suppressed hCG-induced expression of PKA pathway-associated genes, whereas inhibition of PKC pathway-associated genes was predominantly observed following LHR2 blockade. Consistently, the PKA inhibitor H89 and PKC inhibitor GO-6983 reduced hCG-induced expression of steroidogenesis-related genes. Transcriptomic analysis further revealed extensive transcriptional changes and enrichment of pathways associated with ovarian steroidogenesis, ECM–receptor interaction, JAK-STAT, Hippo, and cGMP-PKG signaling. Collectively, these findings support the involvement of both LHR paralogues in late ovarian maturation, with LHR1 predominantly associated with PKA signaling and LHR2 exhibiting a broader signaling profile involving both PKA- and PKC-associated pathways.