Molecular Cell Biological Study on The Estimation of Egg Quality in Fish

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In this study, the stage of meiotic division and the oocyte maturation related protein ; maturation-promoting factor (MPF ; complex of cdc2 and cyclin B) in ovulated eggs from artificially matured eels and from goldfish were examined to assess whether these parameters are related to the egg quality.Female Japanese eels had been induced to mature by repeated injections of salmon pituitary homogenate, followed by injection of 17α,20β-dihydroxy-4-pregnen-3-one to induce ovulation. Grabid female goldfish were injected of HCG to induce ovulation. Ovulated eggs were analyzed by histological observation to determine the stage of meiotic division, and by Western blotting to investigate MPF.In Japanese eel, eggs at high fertilization rate were mainly composed of eggs at metaphase II stage. In contrast, eggs at low fertilization rate had many abnormal stages of the meiotic division. The anti-cdc2 antibody recognized two bands (35, 37 kDa) in ovulated eggs. And anti-cyclin B antibodies recognized 50 kDa (cyclin B1) and 52 kDa (cyclin B2) bands in ovulated eggs. Especially, the intensity of the bands for cyclin B1, cyclin B2 and 35kDa cdc2 were correlated with fertilization rate. In goldfish, the fertilization rate was decreased as time passed. However, there was no relationship between the fertilization rate and stages of the meiotic division in the ovulated eggs. These results suggest that one of the cause of deterioration in egg quality in Japanese eel is abnormality of oocyte maturation such as meiotic division process. However, deterioration of egg quality in goldfish is considered that the cytoplasm has some cause.