Origin and evolutionary landscape of Nr2f transcription factors across Metazoa

Abstract

Background: Nuclear Receptor Subfamily 2 Group F (Nr2f) orphan nuclear hormone transcription factors (TFs) are fundamental regulators of many developmental processes in invertebrates and vertebrates. Despite the importance of these TFs throughout metazoan development, previous work has not clearly outlined their evolutionary history. Results: We integrated molecular phylogeny with comparisons of intron/exon structure, domain architecture, and syntenic conservation to define critical evolutionary events that distinguish the Nr2f gene family in Metazoa. Our data indicate that a single ancestral pre-metazoan Nr2f gene, we have termed Nr2f1/2/5/6, predated six main Bilateria subfamilies, which include a single Nr2f1/2/5 homolog that is present throughout protostomes and invertebrate deuterostomes, Nr2f1/2 homologs in agnathans, and Nr2f1 , Nr2f2 , Nr2f5 , Nr2f6 orthologs that are found in gnathostomes. The three Nr2f1/2 members in agnathans are due to independent expansions not found in gnathostomes, while the vertebrate Nr2f1 , Nr2f2 , Nr2f5 members arose from whole-genome duplications (WGDs). However, Nr2f6 members are the most divergent subfamily, likely originating from an ancient duplication, and are only retained by gnathostomes. Interestingly, Nr2f5 TFs have been independently lost in both cartilaginous fish and amniotes, such as humans. Furthermore, our analysis shows there are differential expansions and losses of Nr2f genes in teleosts following their additional rounds of WGDs. Conclusion: Overall, our evolutionary genomic analysis of Nr2f proteins helps to reveal the origins and previously unrecognized relationships of this ancient transcription factor family, which may allow for greater insights into the conservation of Nr2f functions that shape Metazoan body plans.