Liver X receptors, LXRs, are ligand-activated transcription factors that belong 
to the group H nuclear receptor (NR) superfamily. In this study, an LXR (HrLXR) 
cDNA was cloned from the ascidian Halocynthia roretzi hepatopancreas and 
characterized to examine the functional conservation of ancestral LXRs in 
chordates. A phylogenetic analysis of HrLXR showed that it belongs to the 
tunicate (urochordate) LXR subgroup, which is distinct from vertebrate LXRs. 
Quantitative real-time PCR analysis revealed that HrLXR mRNA was expressed 
predominantly in the gills, and highly expressed in unfertilized eggs followed 
by decrease at later embryonic and larval stages. Unexpectedly, HrLXR was not 
activated by GW3965, whereas a synthetic ligand for a farnesoid X receptor, 
GW4064, activated HrLXR. This activation was abolished by the deletion of 51 
amino acids from the N-terminus. In a mammalian two-hybrid system, HrLXR 
interacted with HrRXR in the presence of GW4064 or 9-cis retinoic acid. The 
injection of GW3965 and GW4064 in vivo increased the ATPbinding cassette 
sub-family G member 4 and HrLXR mRNA levels in the hepatopancreas and gills. 
These results suggest that the mRNA expression and transcriptional properties of 
HrLXR are different from those of vertebrate LXRs, although HrLXR is likely 
responsive to the related NR ligand, GW4064.