Identification and characterization of a novel fushi tarazu factor 1 (FTZ-F1) nuclear receptor in Schistosoma mansoni.

Fushi-tarazu factor-1 (FTZ-F1) is an orphan nuclear receptor involved in gene regulation of various developmental processes and physiological activities. We identified a new member of ftz-f1 gene in Schistosoma mansoni, termed Smftz-f1alpha. The Smftz-f1alpha gene has a complex structure with 15 exons interrupted by 14 introns. It encodes an unusually long SmFTZ-F1alpha protein of 1892 amino acids containing all the modular domains found in nuclear receptors. The DNA-binding domain (DBD) of SmFTZ-F1alpha is conserved and most similar to those of human and mouse FTZ-F1 orthologues, exhibiting a 76% identity. The ligand-binding domain (LBD) is less conserved than the DBD; it shares more diverse identity scores in different regions ranging from 23% to 42% in region II and 28% to 72% in region III. A conserved activation function-2 (AF-2) sequence is present in the SmFTZ-F1alpha LBD. This protein also contains a long hinge region (1027 aa) and an F region (220 aa) at the carboxyl end. Phylogenetic analysis suggests that SmFTZ-F1alpha is the orthologue of Drosophila FTZ-F1alpha and vertebrate NR5 members. Western blot analysis of a schistosome extract identified two proteins, one with a size (206 kDa) predicted by the SmFTZ-F1alpha cDNA sequence and a smaller component of 120 kDa. Smftz-f1alpha is expressed throughout the schistosome life cycle with the highest expression in the egg stage. SmFTZ-F1alpha mRNA is widely distributed in adult worms but does not appear in vitelline cells of female worms. SmFTZ-F1alpha localizes to a variety of tissues but is most abundant in the testis of the male and the ovary of female worms. Our results suggest that SmFTZ-F1alpha plays a role in regulating schistosome development and sexual differentiation similar to other FTZ-F1 family members.