A unique nuclear receptor direct repeat 17 (DR17) is present within the upstream region of Schistosoma mansoni female-specific p14 gene

The eggs produced by sexually mature female Schistosma mansoni are responsible for the pathogenesis of the disease. The eggshell precursor gene p14 is expressed only in the vitelline cells of sexually mature female worms in response to a yet unidentified male stimulus. Herein, we report the identification of a novel nuclear receptor response element in the upstream region of the p14 gene. This element contains the canonical hexameric DNA core motif, 5'-PuGGTCA, composed of an atypically spaced direct repeat (DR17). Schistosome nuclear receptors SmRXR1 and SmNR1 specifically bound to the p14-DR17 element as a heterodimer. SmRXR1, but not SmNR1, bound to the motif as a monomer. Introduction of mutations in the TCA core sequence completely abolished the binding by SmRXR1/SmNR1 heterodimer. This finding supports our hypothesis that the expression of Schistosoma mansonip14 gene is regulated through the nuclear receptor signaling pathway.