Schistosoma mansoni: Characterization of Excretory-Secretory Polypeptides Synthesized in Vitro by Daughter Sporocysts

Abstract

Excretory-secretory (ES) products of daughter sporocysts have been implicated in the modulation of snail host reproductive physiology. Because of the potentially important role of ES products in snail reproduction, newly synthesized ES polypeptides of in vitro-cultured Schistosoma mansoni daughter sporocysts were examined in pulse-chase studies using [35S]methionine followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), fluorography, and scanning densitometry. Fluorograms of SDS-PAGE-separated ES proteins revealed that sporocysts released a wide variety of polypeptides ranging in molecular weight from 17 to 200 kDa into supernatants during 6 days of in vitro culture at 26°C. Moreover, the general pattern of synthesis and release of daughter sporocyst polypeptides into culture supernatants differed from those ES components previously described from primary or mother sporocysts. Although quantitative densitometry revealed that total labeled ES protein released into culture supernatants was consistent for an three pulse-chase periods, there were significant differences in the quantities of individual polypeptide peaks. The dynamics of the synthesis and release of eight polypeptides chosen for further analysis varied over time. Several ES polypeptides (110, 95, and 25 kDa) were released in relatively constant amounts, while some (69 and 44 kDa) increased and others (38 and 35 kDa) decreased in quantity over the same period of culture. It is hypothesized that the 38- and 35-kDa polypeptides may be important candidate inhibitory molecules because of the correlation between their early release into culture supernatants and the inhibitory effect of Day 1-2 daughter sporocyst ES products on polysaccharide synthesis in the albumen gland of the snail host. This study firmly establishes that schistosome daughter sporocysts are able to regulate the synthesis and release of certain polypeptides into culture supernatants. The possible roles of secondary sporocyst ES products in altering various aspects of host-parasite physiological interactions are discussed.