Molecular cloning of Nicol1 and expression analysis of reproduction-related genes in the spotted scat (Scatophagus argus)

Peptides are essential bioactive molecules that regulate diverse physiological functions in organisms. Although the Nicol1 has been mainly studied in mammals, its function in teleosts remains poorly characterized. Here, nicol1 was cloned and characterized in Scatophagus argus to determine its structure, expression, and neuroendocrine role. The full-length cDNA is 405 bp, containing a 273 bp ORF encoding a 90 amino acid peptide with a 26-residue signal peptide and a 17-residue mature peptide. Phylogenetic and structural analyses showed that Nicol1 is highly conserved among teleosts, especially Perciformes. qRT-PCR revealed high expression in the brain, pituitary, and gonads of both sexes, indicating involvement in the HPG axis. Immunohistochemistry localized Nicol1 in neuronal cells and spermatogenic and oocytic cells, supporting roles in neuroendocrine regulation and gametogenesis. In vitro incubation of hypothalamic and pituitary tissues with synthetic Nicol1 peptide significantly upregulated multiple gonadotropin-releasing hormone (GnRH) isoforms and downstream gonadotropins (fsh and lh), with pronounced effects observed after 6 h, indicating a time-dependent activation of the reproductive endocrine axis. 17β-estradiol (E2) significantly increased nicol1 expression in the hypothalamus and pituitary, while ER antagonists induced tissue-specific effects, suggesting regulation via nuclear and membrane-associated estrogen signaling. Overall, these results demonstrate that Nicol1 is an estrogen-sensitive peptide that remains functionally unexplored in teleost integrating steroidal and neuroendocrine regulation within the HPG axis of S. argus , with potential relevance for aquaculture breeding strategies. • Nicol1 was cloned and characterized in Scatophagus argus , showing high structural conservation among teleosts. • Nicol1 was highly expressed in the brain, pituitary, and gonads and localized in neuroendocrine and germ cells. • Nicol1 activated GnRH variants and gonadotropins ( fsh and lh ) and was positively regulated by 17β-estradiol, indicating an estrogen-sensitive role in the HPG axis.