MOLECULAR ENDOCRINOLOGICAL STUDY ON MECHANISMS OF ARTIFICIAL MATURATION IN FEMALE JAPANESE EEL

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1) Mechanism of pituitary GTH productionChanges in mRNA levels of GTH Iβ and IIβ subunits in pituitary of Japanese eel were examined during artificial maturation. The level of Iβ dramatically decreased immediately after the start of the treatment of artificial maturation, while the level of IIβdramatically increased. Experiment of pituitary organ culture revealed that estrogen and androgen strongly supressed the expression of Iβ, while they stimulated the expression of IIβ.2) Mechanism of ovarian sterod productioncDNAs of P450scc, P450c17, P450arom, 3β-HSD and 17β-HSD were cloned from Japanese eel ovary. The mRNA levels of ovarian P450scc, P450c17 , P450arom and 17β-HSD gradually increased during artificial maturation although the level of P450arom decreased in final maturation phase, while the level of 3β-HSD did not change.3) Mechanism of liver vitellogenin(VTG) productionThe mRNA levels of VTG1 in liver increased after mid-vitellogenic stage, while the level of VTG2 increased immediately after the start of the treatment of artificial maturation.4) Mechanism of sexual maturation in natural eelThe mRNA levels of GTH Iβ and IIβ in pituitary and various steroidogenic enzymes in ovary were compared between the artificially maturing Japanese eel (JP) and naturally maturing New Zealand longfinned eel (LF). The level of Iβ in LF was higher than that in JP. However, the levels of others were higher in JP than those in LF.