Molecular cloning and localization of the luteinizing hormone beta subunit and glycoprotein hormone alpha subunit from Japanese anchovy Engraulis japonicus.

Although Clupeiformes contain many economically important species, there is limited information on their reproductive physiology. To obtain more insight into reproductive mechanisms in clupeiform fishes, molecular cloning of the Japanese anchovy Engraulis japonicus luteinizing hormone beta (LHbeta) and glycoprotein hormone alpha (GPHalpha) subunits, and immunocytochemistry of gonadotrophs in the pituitary using antisera raised against the synthetic peptides for both subunits were carried out. The cDNAs for LHbeta and GPHalpha subunits consisted of 963 and 535 nucleotides encoding 141 and 122 amino acids, respectively. The deduced amino acid sequences of the E. japonicus LHbeta subunit showed a 60% similarity to the Pacific herring Clupea pallasii LHbeta subunit and 24-31% similarities to FSHbeta subunits of other fish species. The E. japonicus GPHalpha subunit showed 52-57% similarities to anguilliform and cypriniform GPHalpha subunits. Both the subunits have typical structural characteristics of each subunit such as N-linked glycosylation sites, conserved cysteine residues and highly conserved short amino acid sequences. These results indicate that cDNAs cloned in this study encode the E. japonicus LHbeta and GPHalpha subunits. Reverse-transcription polymerase chain reaction (RT-PCR) revealed that both the LHbeta and GPHalpha subunit genes were abundantly expressed in the pituitary, and the GPHalpha subunit was observed to be weakly expressed in the extrapituitary tissues. Immunocytochemistry of the E. japonicus pituitary showed that cells that immunoreacted with antiserum against the LHbeta subunit were distributed in the peripheral regions of proximal pars distalis, and these cells were also immunoreactive to antiserum against the GPHalpha subunit. An abundant number of both LHbeta and GPHalpha cells in the pituitary of matured fish were observed, in comparison with immature fish. These results indicate that the E. japonicus LH is involved in the final reproductive maturation as well as those of other teleosts.