MOLECULAR MECHANISMS OF VITELLOGENESIS IN JAPANESE EEL

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Estrogen receptors were idenified in cytosolic nuclear extracts of livers of female Japanese eel. The changes in cytosolic estrogen receptor (ER) levels represent increased hepatic responsiveness to estrogenic stimuli during maturation. In contrast, nuclear ER levels did not change singnificantly. In addition, cDNA encoding ER was isolated and sequenced. This cDNA contains a comlete open reading frame encoding 573 amino acid residues. The amino acid sequence of the eel ER showed high homology of the DNA binding (80 %) and ligand binding (55 %) domains with those of other species. cDNA fragment encoding vitellogenin (VTG) was also isolated. Using these cDNA as the probe, changes in the ER and VTG gene expression were examined in the liver during maturation. Changes in the levels of both ER and VTG mRNA were well corrclated with canges in that of blood estrogen. Furthermore, Establishment of hepatic cell cuture system and development of sensitive assay system for VTG revealed that the capacity to produce VTG in hepatic cell from female liver was far higher than that from male.