FTZ-F1-RELATED ORPHAN RECEPTORS IN XENOPUS-LAEVIS - TRANSCRIPTIONAL REGULATORS DIFFERENTIALLY EXPRESSED DURING EARLY EMBRYOGENESIS

Orphan receptors of the FTZ-F1-related group of nuclear receptors (xFF 1r) were identified in Xenopus laevis by isolation of cDNAs from a neu rula stage library. Two cDNAs were found, which encode full-length, hi ghly related receptor proteins, xFF1rA and B, whose closest relative k nown so far is the murine LRH-1 orphan receptor. xFF1rA protein expres sed by a recombinant vaccinia virus system specifically binds to FTZ-F 1 response elements (FRE; PyCAAGGPyCPu). In cotransfection studies, xF F1rA constitutively activates transcription, in a manner dependent on the number of FREs. The amounts of at least four mRNAs encoding full-l ength receptors greatly increase between gastrula and early tailbud st ages and decrease at later stages. At early tailbud stages, xFTZ-F1-re lated antigens are found in all nuclei of the embryo.