Figure 4

Evolutionary diversification of the NR superfamily in animals. At left is a cartoon of the metazoan tree showing the evolutionary relationships between ctenophores, sponges, placozoan, cnidarians, and bilaterians (that is, protostomes and deuterostomes). Due to current controversy about the branching order of the early diverging metazoans (see main text), the placement of lineages differs depending on particular analyses and thus an inference for the timing of origin and lineage-specific loss of particular NR families would vary. Colored boxes indicate a NR subfamily is represented by one or more genes for that species. The "inferred bilaterian ancestor" is based largely on a phylogenetic analysis conducted by Bertrand et al. [1]. However, two of these subfamilies are restricted to either protostomes (5B) or deuterostomes (3C) and we have shaded these and used black text to reflect a lack of conclusive support for the presence of these subfamilies in the bilaterian ancestor. Despite the absence of some genes in the D. melanogaster genome, studies of NRs from other protostomes (NR1A from Schistosoma mansoni [50] and NR3A from mollusks and annelids [51, 52]) indicate that these subfamilies were present in the bilaterian ancestor and secondarily lost from Drosophila. Similarly, members of NR1B and 1C have been reported in mollusks and annelids [10], and thus are not restricted to deuterostomes. * The sponge Amphimedon queenslandica has two NRs, one that is supported as an ortholog to HNF4 (NR2A) and a second that groups between subfamily NR2A and the rest of the NR superfamily [see also [10]].