Photoreceptor-specific nuclear receptor (PNR/NR2E3) and Tailless homolog (TLX/NR2E1) are human orthologs of the NR2E group,
a subgroup of phylogenetically related members of the nuclear receptor (NR) superfamily of transcription factors. We assessed the
ability of these NRs to form heterodimers with other members of the human NRs representing all major subgroups. The TLX
ligand-binding domain (LBD) did not appear to form homodimers or interact directly with any other NR tested. The PNR LBD was
able to form homodimers, but also exhibited robust interactions with the LBDs of peroxisome proliferator-activated receptor-γ
(PPARγ)/NR1C3 and thyroid hormone receptor b (TRb) TRβ/NR1A2. The binding of PNR to PPARγ was specific for this paralog, as
no interaction was observed with the LBDs of PPARα/NR1C1 or PPARδ/NR1C2. In support of these findings, PPARγ and PNR were
found to be co-expressed in human retinal tissue extracts and could be co-immunoprecipitated as a native complex. Selected
sequence variants in the PNR LBD associated with human retinopathies, or a mutation in the dimerization region of PPARγ LBD
associated with familial partial lipodystrophy type 3, were found to disrupt PNR/PPARγ complex formation. Wild-type PNR, but not
a PNR309G mutant, was able to repress PPARγ-mediated transcription in reporter assays. In summary, our results reveal novel
heterodimer interactions in the NR superfamily, suggesting previously unknown functional interactions of PNR with PPARγ and
TRβ that have potential importance in retinal development and disease.