Development and validation of enzyme-linked immunosorbent assays specific for follicle-stimulating hormone and luteinizing hormone in Japanese eel

Abstract

Two types of gonadotropins (Gths), follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh), are primary regulators of reproduction in vertebrates, including teleost fish. In this study, recombinant Japanese eel Gths (reGth; reFsh and reLh), and recombinant chimeric Gths (rcGth; rcFsh and rcLh), consisting of an eel β-subunit with rabbit glycoprotein hormone α-subunit, were produced as single-chain proteins, using a mammalian expression system and subsequently highly purified. Antibodies raised against rcGths were affinity purified with the corresponding reGth, and specific enzyme-linked immunosorbent assays (ELISAs) for Japanese eel Fsh and Lh were developed using these antibodies for the first time. The ELISAs were sensitive and parallelism was seen between the standard curve and serial dilutions of Japanese eel serum and pituitary extract (PE). Contents of Fsh and Lh protein in the pituitaries of the female Japanese eel at the pre-vitellogenic stage were comparable and the Lh contents at the migratory nucleus stage were highly induced during artificial induction of maturation by injections of salmon PE. Furthermore, the accumulated Lh was released at a high level by administration of a Lh-releasing hormone analogue and pimozide. Recombinant Gths and homologous ELISAs established for Japanese eel may be useful tools for studying reproductive eel biology.