Isolation of prolactin gene and its differential expression during metamorphosis involving eye migration of Japanese flounder Paralichthys olivaceus.

Abstract Eye migration during flatfish metamorphosis is driven by asymmetrical cell proliferation. To Fig. out Prolactin (PRL) function in this process, the full-length cDNA of prl was cloned from Japanese flounder (Paralichthys olivaceus) in our study. The deduced PRL protein shares highly conserved sequence with other teleosts, but has several amino acids loss compared with higher vertebrates, including amphibians, reptiles, avian and mammals. Spatio-temporal expression of prl gene displayed its extensive expression in the early development stages, while the limited expression of prl was observed in the pituitary, brain, and intestine of adult fish. In situ hybridization showed the asymmetrical distribution patterns of prl gene around the eyes during metamorphosis, which was coincident with the cell proliferation signals. Colchicine inhibits cell proliferation and reduces the prl gene expression, which indicates that PRL is involved in cell proliferation in the suborbital area of the migrating eye. The treatment of methimazole and 9-cis-retinoic acid respectively led to a reduction in the number of proliferating cells and the downregulation of prl expression, suggesting PRL is regulated by thyroid hormone signaling pathway and retinoic acid related signaling pathways. The results gave us a basic understanding of PRL function during flatfish metamorphosis.