Identification and partial characterization of Olyra longicaudata(McClelland, 1842) vitellogenins: Seasonal variation in plasma,relative to estradiol-17 and ovarian growth

Abstract

tThis study aims at immunochemical characterization of plasma vitellogenin (VTG), development of anheterlogous VTG ELISA and to relate seasonal variation in plasma VTG and estradiol-17 (E2) levels withovarian growth (gonadosomatic index, GSI) in Olyra longicaudata (McClelland, 1842), a rare hill-streamcatfish endemic to North East India. On native PAGE, plasma from E2-injected male, vitellogenic as well asgravid females, but not untreated male, resolved into two major protein bands. These two proteins stainedpositive for carbohydrate, lipid and phosphorous, albeit with differential intensity and cross-reacted wellwith catfish VTG antiserum (a-VTG) suggesting them as putative VTGs in circulation. Ammonium sul-phate (50%) fractionation followed by SDS-PAGE analysis of E2-treated male plasma resolved into fourprotein bands (150–15 kDa), of which two, with molecular mass of 150 and 130 kDa cross-reacted witha-VTG indicating them as VTG monomers. Immunoprecipitation of E2-induced plasma and immunoblotanalysis of crude yolk proteins with a-VTG revealed two proteins in each case indicating two forms ofVTG, present in circulation, possibly act as yolk precursors. Competitive antigen-capture ELISA developedearlier for catfish, Clarias batrachus VTG (CF-VTG1), revealed parallel binding slopes between dilutioncurves of plasma from vitellogenic female, E2-treated male and CF-VTG1 standard. Congruent with grad-ual increase in plasma E2, ovarian weight and appearance of vitellogenic and yolky oocytes, VTG levelin circulation increased sharply in May–June, reaching the peak value in July, dropped sharply duringAugust–September and was undetected or negligible in amount during December allowing identificationof the ripening, the pre-spawning, the spawning and the quiescent phases respectively.