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First published online June 15, 2006
Journal of Experimental Biology 209, 2567-2575 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02270

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2-hydroxyestradiol-17ß-induced oocyte maturation: involvement of cAMP–protein kinase A and okadaic acid-sensitive protein phosphatases, and their interplay in oocyte maturation in the catfish Heteropneustes fossilis

A. Mishra and K. P. Joy^*

Department of Zoology, Banaras Hindu University, Varanasi-221005, India

^* Author for correspondence (e-mail: kpjoy{at}bhu.ac.in)

Accepted 13 April 2006

In Heteropneustes fossilis, in vitro incubation of postvitellogenic follicles with 2-hydroxyestradiol-17ß (2-OHE₂, 5 µmol l^–1) decreased significantly the total cAMP level, concomitant with germinal vesicle breakdown (GVBD). The incubation of the follicles with cAMP or cAMP-elevating drugs [phosphodiesterase (PDE) inhibitors], such as IBMX (3-isobutyl-1-methyl-xanthine), theophylline and caffeine, inhibited the 2-OHE₂-induced GVBD in a concentration-dependent manner. The magnitude of the response varied: both cAMP and IBMX were effective at all concentrations (0.1–2.0 mmol l^–1), followed by theophylline (0.5–2.0 mmol l^–1) and caffeine (1–2.0 mmol l^–1). The protein kinase A (PKA) inhibitor H89 stimulated oocyte maturation in a concentration-dependent manner. However, when co-incubated with 2-OHE₂ for 24 h it produced a biphasic effect: low concentrations (0.1 and 1.0 µmol l^–1) did not alter the 2-OHE₂-induced GVBD, but high concentrations (5 and 10 µmol l^–1) inhibited it. The incubation of the follicles with H89 lowered the inhibitory effect of IBMX on the 2-OHE₂-induced GVBD. The incubation of the follicles with okadaic acid (OA), a protein phosphatase 1 and 2A inhibitor did not affect GVBD but when co-incubated with 2-OHE₂, it enhanced the GVBD response. OA reversed the inhibitory effect of IBMX. The results suggest that OA may overcome the inhibition of 2-OHE₂-induced GVBD by IBMX at a step distal to the cAMP–PKA pathway.

Key words: catfish, 2-hydroxyestradiol, GVBD, cAMP, protein kinase A, protein phosphatases, okadaic acid