Production of recombinant Japanese eel gonadotropins by baculovirus in silkworm larvae

Recombinant follicle-stimulating hormone (reFSH) and luteinizing hormone (reLH) of the Japanese eel Anguilla japonica were produced by baculovirus in silkworm Bombyx mori larvae. cDNAs encoding Japanese eel gonadotropin subunits (i.e., FSHβ, LHβ, and common α) were introduced into the baculovirus, which was infected into silkworm larvae after propagation of the recombinant virus in B. mori culture cells. A 100 ml solution of pooled hemolymph from silkworm larvae containing reFSH or reLH were obtained from approximately 250 infected larvae. Ten milliliters of hemolymph were applied to Ni-affinity choromatography, and 5.6 and 3.5 mg of partially purified reFSH and reLH were obtained, respectively. Using Western blot analysis concentrations of reFSH and reLH in the original hemolymph was estimated to be 2.2 and 1.1 mg/ml, respectively. Biological activities of reFSH and reLH were assessed in vitro and in vivo. Purified reFSH and reLH induced eel oocyte maturation in vitro, and administration of hemolymph containing reFSH or reLH induced spermatogenesis in vivo in sexually immature Japanese eel. The present study indicates that a baculovirus–silkworm system could produce large amounts of biologically active recombinant fish gonadotropins for use in investigations in reproductive endocrinology and/or aquaculture of fish.