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 of uts2r3 results in severe scoliosis in adult zebrafish. In the present study, we report for the first time the occurrence of urp2, but not of urp1, in two tetrapod species of the Xenopus genus. In X. laevis, we show that urp2 mRNA-containing cells are CSF-contacting neurons. Furthermore, we identified utr4, the X. laevis counterparts of zebrafish uts2r3, and we demonstrate that, as in zebrafish, it is expressed in the dorsal somatic musculature. Finally, we reveal that, in X. laevis, the disruption of utr4 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.

Urp1 和 Urp2 是在硬骨鱼中发现的 urotensin II 家族的两种神经肽，主要在接触脑脊液 (CSF) 的神经元中表达。最近有人提出，正确的轴形成和维护需要 Urp1 和 Urp2。它们的作用被认为是由受体 Uts2r3 介导的，该受体在背体节中特异性表达。为支持这一观点，已证明uts2r3的缺失会导致成年斑马鱼出现严重的脊柱侧弯。在本研究中，我们首次报告了urp2而非urp1在非洲爪蟾属的两种四足动物中的出现。在X. laevis中，我们表明urp2含有 mRNA 的细胞是 CSF 接触神经元。此外，我们确定了utr4，斑马鱼uts2r3的X. laevis对应物，并且我们证明，与斑马鱼一样，它在背部躯体肌肉组织中表达。最后，我们发现，在蟾蜍中，utr4的破坏导致蝌蚪前后轴的异常弯曲。总之，我们的结果表明，Utr4 信号通路在控制身体直线度方面的作用是骨脊椎动物的祖先特征，而不仅仅是辐鳍鱼的特性。