Regulation of the two kiss promoters in goldfish (Carassius auratus) by estrogen via different ERalpha pathways

Kisspeptin stimulates the synthesis and release of gonadotropin via controlling the secretion of gonadotropin releasing hormone in vertebrates. It also mediates the positive or negative feedback regulation of sex steroids on the hypothalamus-gonadotropic axis. In contrast to mammals, two paralogous genes of kisspeptin (kiss1 and kiss2) have been identified in several teleosts, implying the multiplicity of their physiological functions. In the present study, we cloned the promoters of kiss1 and kiss2 genes in goldfish (Carassius auratus), and identified the presence of putative binding sites for estrogen receptors, glucocorticoid receptors, Sp1, AP1, C/EBP and Oct-1. We further demonstrated that the goldfish Kiss neurons co-express the estrogen receptors, with era1 and erb1 in the habenula Kiss1 neurons and era1, era2 and erb1 in the preoptic and hypothalamic Kiss2 neurons. Using transient transfection in HEK293T cells of the two goldfish kiss gene promoters cloned upstream of a luciferase reporter, estrogen (E2, 17b-estradiol) treatment was shown to enhance the promoter activities of the two goldfish kiss genes in the presence of ERa. Deletion analysis of kiss1 promoter indicated that the E2-induced promoter activity was located between position 633 and 317 where no half ERE motifs were found. Point mutation studies on the kiss2 promoter indicated that the E2-stimulated promoter activity was mediated by a half ERE site located at position 57. Results of the present study provide evidence that E2 is capable of exerting positive feedback regulation on the expression of kiss1 and kiss2 in goldfish via ERE-independent or ERE-dependent ERa pathway, respectively.