Gonadotropin triggers the generation of proteinaceous factor in vitellogenic perch (Anabas testudineus) oocyte which stimulates ovarian aromatase activity.

ABSTRACT

Oocytes of vitellogenic stage were collected from A. testudineus and incubated in vitro for 4 hr in the absence (control) or presence of 500 ng of piscine gonadotropic hormone (GtH). After the termination of incubation, oocytes were repeatedly washed and then homogenized and ultracentrifuged at 100,000 g to obtain the supernatant fraction (100K sup). Addition of 100K sup from GtH treated oocytes to the oocyte incubation caused a 3-fold increase in ovarian aromatase activity as compared to the control, whereas 100K sup from control oocytes had no such stimulatory activity. Addition of cycloheximide (50 micrograms/ml) along with GtH blocked the stimulatory effect of 100K sup. Treatment of 100K sup from GtH incubate with pepsin or heat also destroyed its stimulatory effect. All these indicate proteinaceous nature of the factor. This factor was purified to 161-fold by utilizing Sephadex G-75 and DEAE Sephacel chromatography. Addition of increasing concentrations of partially purified GtH induced protein (GIP) to oocyte incubation caused a dose dependent increase in ovarian aromatase activity. Both dbcAMP and forskolin mimicked GIP activity. Results indicate that GtH induces the synthesis of a protein factor in perch oocytes which stimulates aromatase activity via the mediation of cAMP.