Cloning and developmental expression of five estrogen-receptor related genes in the zebrafish

Estrogen-receptor related receptors (ERRalpha, beta and gamma) are so-called orphan (i.e. for which no natural ligand has been identified to date) nuclear receptors that are closely related to the estrogen receptors. To gain insights into the possible functions of ERRs during early development, we have cloned their homologs in the zebrafish. Five err cDNA types were recovered in a PCR screen. Transient transfection experiments indicated that zebrafish ERRalpha, ERRgamma and ERRdelta display transcriptional activities that are identical to those of their mammalian counterparts. The expression patterns of err genes were determined during zebrafish development. Tissues such as the hindbrain or the pronephric tubes express several errs whereas others, such as the presumptive mesoderm at the level of the margin, specifically express a single err. Our analysis also points to tissues in which err expression is conserved through evolution, such as slow muscles that specifically express erralpha, suggesting important functions in these tissues.