Conserved role of the urotensin II receptor 4 signalling pathway to control body straightness in a tetrapod

Urp1 and Urp2 are two neuropeptides of the urotensin II family identified in teleost fish and mainly expressed in cerebrospinal fluid (CSF)-contacting neurons. It has been recently proposed that Urp1 and Urp2 are required for correct axis formation and maintenance. Their action is thought to be mediated by the receptor Uts2r3, which is specifically expressed in dorsal somites. In support of this view, it has been demonstrated that the loss ofuts2r3 results in severe scoliosis in adult zebrafish. In the present study, we report for the first time the occurrence ofurp2, but not ofurp1 , in two tetrapod species of theXenopus genus. InX. laevis , we show thaturp2 mRNA-containing cells are CSF-contacting neurons. Furthermore, we identifiedutr4, theX. laevis counterparts of zebrafishuts2r3, and we demonstrate that, as in zebrafish, it is expressed in the dorsal somatic musculature. Finally, we reveal that, inX. laevis, the disruption ofutr4 results in an abnormal curvature of the antero-posterior axis of the tadpoles. Taken together, our results suggest that the role of the Utr4 signalling pathway in the control of body straightness is an ancestral feature of bony vertebrates and not just a peculiarity of ray-finned fishes.