Identification of a cDNA encoding a retinoid X receptor homologue from Schistosoma mansoni - Evidence for a role in female-specific gene expression

Schistosoma mansoni, a multicelluar eukaryotic blood fluke, is a major caus e of morbidity worldwide in humans. The study of female parasite growth, de velopment, and gene regulation is important because the eggs produced are r esponsible for the pathogenesis observed in schistosomiasis, p14, an eggshe ll precursor gene expressed only in sexually mature females in response to a male stimulus, is a model for female-specific gene regulation. The upstre am region of the p14 gene shares sequences present in insect genes known to be regulated in a sex-, temporal-, and tissue-specific manner by members o f the steroid receptor superfamily, Herein, we report the identification an d characterization of a cDNA that encodes the S, mansoni (Sm) RXR homologue , Sequence analysis predicts and Western blot analysis confirms the synthes is of a 74-kDa protein, the largest member of the RXR family reported to da te. We show by electrophoretic mobility shift assay analysis that SmRXR bin ds to cis-elements of the p14 gene including a direct repeat that follows t he "3-4-5" rule of binding elements recognized by members of the steroid re ceptor superfamily, Furthermore, we demonstrate that SmRXR can act as a tra nscription activator in the yeast one-hybrid system. Through quantitative r everse transcriptase-polymerase chain reaction, we show that the SmRXR gene is constitutively expressed and thus must play multiple roles throughout t he schistosome life cycle.