A functionally conserved member of the FTZ‐F1 nuclear receptor family from Schistosoma mansoni

Abstract

The fushi tarazu factor 1 (FTZ-F1) nuclear receptor subfamily comprises orphan receptors with crucial roles in development and sexual differentiation in vertebrates and invertebrates. We describe the structure and functional properties of an FTZ-F1 from the platyhelminth parasite of humans, Schistosoma mansoni, the first receptor from this family to be characterized in a Lophotrochozoan. It contains a well conserved DNA-binding domain (55-63% identity to other family members) and a poorly conserved ligandbinding domain (20% identity to that of zebrafish FF1a). However, both the ligand domain signature sequence and the activation function 2-activation domain (AF2-AD) are perfectly conserved. Phylogenetic analysis confirmed that SmFTZ-F1 is a member of nuclear receptor subfamily 5, but that it clustered with the Drosophila receptor DHR39 and has consequently been named NR5B1. The gene showed a complex structure with 10 exons and an overall size of 18.4 kb. Two major transcripts were detected, involving alternative promoter usage and splicing of the two 5¢ exons, but which encoded identical proteins. SmFTZ-F1 mRNA is expressed at all life-cycle stages with the highest amounts in the larval forms (miracidia, sporocysts and cercariae). However, expression of the protein showed a different pattern; low in miracidia and higher in adult male worms. The protein bound the same monomeric response element as mammalian SF-1 (SF-1 response element, SFRE) and competition experiments with mutant SFREs showed that its specificity was identical. Moreover, SmFTZ-F1 transactivated reporter gene transcription from SFRE similarly to SF-1. This functional conservation argues for a conserved biological role of the FTZ-F1 nuclear receptor family throughout the metazoa.Keywords: platyhelminth; development; orphan receptor; phylogeny; DNA-binding.The FTZ-F1 gene subfamily encodes orphan nuclear receptors and appears to be present in all metazoan phyla [1]. The first member of the subfamily, FTZ-F1a, was isolated from Drosophila melanogaster [2,3] and was identified both as a transcriptional regulator and cofactor [4,5] of the homeodomain protein fushi tarazu (FTZ), a segmentation gene of the pair-rule class responsible for the formation of alternative segmental units in the D. melanogaster embryo [6]. FTZ-F1a is expressed in early embryos, concomitant with FTZ expression. A second isoform, FTZ-F1b, encoded by the same gene [7], is detectable in late-stage embryos through to adults, when FTZ expression is absent, and regulates genes associated with ecdysis and metamorphosis [8]. In the nematode Caenorhabditis elegans, nhr-25, the homologue of FTZ-F1, is required for epidermal and somatic gonad development and also participates in the regulation of moulting [9,10]. In vertebrates, an FTZ-F1 orthologue was first identified as a steroidogenic factor (Ad4BP/SF-1) present in the adrenal gland and able to bind to proximal promoter regions of cytochrome P450 steroid hydroxylase genes (reviewed in [11]). Further studies performed to identify the t...

Schistosoma mansoni (Platyhelminthes, Trematoda) nuclear receptors: Sixteen new members and a novel subfamily

“…By obtaining the entire DBD sequence, we demonstrate that these genes are the partial coding sequence of Sm2DBDα or Sm2DBDβ, thus ERR, E75 and Kirps are not found in S. mansoni (Supplementary Material 9). Our results added to the five previously identified NRs (de Mendonca et al, 2002;de Mendonca et al, 2000b;Freebern et al, 1999a,b) brings the total to 21 NRs for S. mansoni (Fig. 3).…”

“…Of the 22-25 NRs in Urbilateria, five genes (E78, DSF, FAX1, DHR39 and Knirps/KNRL/Eagle) were lost during the evolution of chordates . Three of them, SmE78, SmDSF and a HR39 homologue SmFTZ-F1 (AF158103 (de Mendonca et al, 2002)) were retained in S. mansoni. In Drosophila, E75 and E78 are both directly related to the ecdysone signal (Segraves and Hogness, 1990;Woodard et al, 1994).…”

“…From studies of the origin and diversification of NRs, Escriva et al (1997) identified the partial coding sequence of conserved DBD of 5 S. mansoni NRs (SmRXR, SmFTZ-F1, two COUP-TF and SmTR4). More recently, three full length S. mansoni NRs, SmRXR1, SmRXR2 and SmFTZ-F1, were characterized (de Mendonca et al, 2002(de Mendonca et al, , 2000bFreebern et al, 1999a,b). We initiated our studies on S. mansoni NRs by identifying and characterizing SmRXR1 and SmRXR2 (Freebern et al, 1999a,b).…”

Functions of Nuclear Receptors in Insect Development

“…HR39 is the result of the duplication of the ftz-f1 gene that occurred early during protostomian evolution [94], and hence is most related to SF-1 and LRH-1. In D. melanogaster, DHR39 is induced by 20E and its expression is always inversely related to that of βFTZ-F1 (Figure 3.2), suggesting crossregulatory interactions between both factors [57,95,18].…”

The Schistosoma mansoni transcriptome: An update

“…Differentially spliced genes, linked to development or sex, for example, are increasingly being observed in schistosomes (Shoemaker et al, 1992;Hamdan and Ribeiro, 1998;De Mendonca et al, 2002;Ram et al, 2004;DeMarco et al, 2006;Bahia et al, 2006). Alternative transcription initiation and polyadenylation sites could also be explored with the use of EST data (Kan et al, 2001;Zavolan et al, 2003;Le, V et al, 2006;Seoighe et al, 2006;Tian et al, 2007).…”