Involvement of mitogen-activated protein kinase in 2-hydroxyestradiol-17beta-induced oocyte maturation in the catfish Heteropneustes fossilis and a note on possible interaction with protein phosphatases.
Mitogen-activated protein kinase (MAPK) was demonstrated in the postvitellogenic follicles (theca-granulosa and oocyte) of catfish by Western blotting using a polyclonal anti-rabbit serum, which recognized both ERK1 and ERK2. Two distinct protein bands resolved in the 46-48 kDa range of 12% SDS-PAGE were immunoblotted. Incubation of the follicles with 5 microM 2-OHE2 elicited GVBD significantly in a duration-dependent manner with a concomitant increase in the expression of MAPK (ERK1 and ERK2). Densitometric analysis of the immunoblots showed significant variations in the intensity of staining. The ERK1 expression increased significantly from 6 h onwards but the changes were less pronounced. On the other hand, ERK2 registered a sharp significant increase after 3h, which paralleled the GVBD response. The MEK inhibitor PD098059 alone did not induce GVBD. Co-incubation of the follicles with 2-OHE2 and PD098059 significantly inhibited the steroid-induced GVBD at all concentrations. Immunoblot analysis showed that PD098059 inhibited MAPK activity significantly compared to the 2-OHE2 group. The addition of okadaic acid (OA) in the incubation medium containing both 2-OHE2 and PD098059 reversed the inhibitory effect of the latter and GVBD was elevated significantly over that of the 2-OHE2 group but significantly lower than that of the 2-OHE2 + OA group. The results suggest an involvement of MAPK in meiotic maturation but the site(s) of action: oocyte, follicular envelope or both needs further investigation.
Department of Zoology, Banaras Hindu University, Varanasi 221005, India.
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Mishra
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D019326:17-alpha-Hydroxyprogesterone / Q000378:metabolism; D000818:Animals; D002397:Catfishes / Q000502:physiology*; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D006908:Hydroxyprogesterones / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism / Q000502:physiology*; D019319:Okadaic Acid / Q000037:antagonists & inhibitors; D009865:Oocytes / Q000187:drug effects* / Q000254:growth & development*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D011374:Progesterone / Q000378:metabolism; D012741:Sexual Maturation / Q000187:drug effects
D005419:Flavonoids; D006908:Hydroxyprogesterones; C007433:17,20-dihydroxy-4-pregnen-3-one; D019319:Okadaic Acid; D011374:Progesterone; D004958:Estradiol; D019326:17-alpha-Hydroxyprogesterone; C001390:2-hydroxyestradiol; D020928:Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one