A NOVEL NUCLEAR RECEPTOR HETERODIMERIZATION PATHWAY MEDIATED BY ORPHAN RECEPTORS TR2 AND TR4

A unique heterodimerization pathway involving orphan receptors TR2 and TR4 is demonstrated. TR2 and TR4 preferentially form heterodimers in solution as well as on DNA elements containing a direct repeat-5 (DR5) , The in vitro interaction between TR2 and TR4 is demonstrated by the yeast and the mammalian two-hybrid interaction assays, the pull-down a ssay, and the gel mobility shift assay, The in vivo interaction is dem onstrated by following the intracellular localization of fusion recept ors tagged with a green fluorescent protein, The dimerization is media ted by the ligand binding domains, and the three leucine residues on h elix 10 of TR2 are critical for this interaction. In addition, coexpre ssion of these two receptors exerts a much stronger repressive activit y on a DR5-containing reporter than expressing either receptor alone. In the developing testis, TR2 and TR4 are coexpressed in the same test icular cell populations and exhibit a parallel pattern of expression a long development. The preferential heterodimerization between TR2 and TR4 and their coexistence in specific germ cell populations suggest a physiological role of TR2/TR4 heterodimers in germ cell development.