Trichoplax, the simplest known animal, contains an estrogen-related receptor: Implications for the evolution of vertebrate and invertebrate estrogen receptors

Although, as their names imply, vertebrate and invertebrate estrogen receptors [ERs] and estrogen-related receptors [ERRs] are related transcription factors, their evolutionary relationships to each other are not fully understood. We searched recently sequenced genome of Trichoplax, the simplest known animal, and genomes from three lophotrochozoans: Capitella, a worm, Helobdella robusta, a leech, and Lottia gigantea, a snail, to elucidate the origins and evolution of ERs and ERRs. BLAST found an ERR in Trichoplax, but no ER. BLAST searches of the lophotrochozaons found ERRs in all three and invertebrate ERs in Capitella and Lottia, but not in Helobdella. These database searches and a phylogenetic analyses indicate that invertebrate ERs arose in a protostome, and vertebrate ERs arose later in deuterostome.