title: Molecular and expression analysis of the farnesoid X receptor in the urochordate Halocynthia roretzi.
abstract: The farnesoid X receptors (FXRs) are the major transcriptional regulators of bile salt synthesis in vertebrates. However, the structural conservation of invertebrate FXRs has only been studied for the major model organisms and studies on additional invertebrate FXRs are clearly required to obtain better resolution of FXR phylogeny and comparative developmental insights in chordates. In the present study, the cDNA encoding the farnesoid X receptor, HrFXR, was cloned from a marine invertebrate Halocynthia roretzi. The open reading frame of HrFXR encoded 688 amino acids including a longer N-terminal region and showed overall sequence identities of 28-41% to vertebrate and Ciona intestinalis FXRs. The N-terminal activation function 1 (AF-1) and hinge domains of HrFXR displayed relatively low identities (<20%), whereas the DNA-binding and ligand-binding domains showed relatively high (>73%) and intermediate (21-50%) identities, respectively. Based on a phylogenetic analysis, HrFXR belonged to a urochordate group, which was placed differently from vertebrate FXRα and FXRβ subgroups. Real-time quantitative PCR analysis revealed that the HrFXR mRNA originated maternally and was highly expressed in adult gonads. Additionally, HrFXR mRNA levels in the gills and hepatopancreas showed significantly higher values in animals with soft tunic syndrome compared to those of normal individuals. Furthermore, direct injection of cholic acid significantly increased HrFXR transcript levels in vivo, although an expression vector containing HrFXR cDNA did not show a significant transactivation function in response to a well-known ligand for vertebrate FXR, GW4064, in HepG2 cells. These results suggest that the tunicate FXR has different structural and expressional characteristics compared to those of vertebrate FXRs.
authors: Department of Marine Molecular Biotechnology, Gangneung-Wonju National University, Gangneung 210-702, Republic of Korea.
authors: Sejung
authors: S
authors: Maeng
authors: Jung Hwan
authors: JH
authors: Lee
authors: Gil Jung
authors: GJ
authors: Kim
authors: Sung Hun
authors: SH
authors: Kim
authors: Hak Cheol
authors: HC
authors: Kwon
authors: Yun Kyung
authors: YK
authors: Shin
authors: Young Chang
authors: YC
authors: Sohn
mesh_terms: D000818:Animals; D018076:DNA, Complementary / Q000235:genetics; D003840:Deoxycholic Acid / Q000494:pharmacology; D004625:Embryo, Nonmammalian / Q000187:drug effects / Q000378:metabolism; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D017930:Genes, Reporter / Q000235:genetics; D056945:Hep G2 Cells; D006801:Humans; D008024:Ligands; D010802:Phylogeny; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics* / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic / Q000187:drug effects; D014561:Urochordata / Q000187:drug effects / Q000196:embryology / Q000235:genetics*; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D018076:DNA, Complementary; D003840:Deoxycholic Acid; D008024:Ligands; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D000099150:Receptor, Farnesoid X-Activated