Figure 7.

Evolution of GPRC5 receptors. Scale bar in million years (mya). Basal taxa (sea squirts, amphioxus and lamprey) have receptor sequences similar to XRAIG4, which is present in frogs, but not in all other vertebrate species. All vertebrates have genes for GPRC5B, GPRC5C and GPRC5A/D, only some bony fish (Ostariophysi) seem to have lost the 5A/D receptor sequence. GPRC5B is duplicated in all bony fish, GPRC5C is duplicated in Acanthopterygii fish. GPRC5A retains at least one ancestral (or plesiomorphic) tetrapod expression domain, in lungs, while GPRC5D may have recruited an ancestral vertebrate skin expression domain into derived, mammalian structures (hair).