Drug Research Program, Division of Pharmaceutical Chemistry and Technology, Faculty of Pharmacy, University of Helsinki, POB 56, 00014, Helsinki, Finland.
Biochemistry and Cell Biology, Department of Veterinary Biosciences, Faculty of Veterinary Medicine, University of Helsinki, POB 66, 00014, Helsinki, Finland.
Sci Rep. 2024 Apr 2;14(1):7690. doi: 10.1038/s41598-024-56508-1.
Tunicates are evolutionary model organisms bridging the gap between vertebrates and invertebrates. A genomic sequence in Ciona intestinalis (CiOX) shows high similarity to vertebrate orexin receptors and protostome allatotropin receptors (ATR). Here, molecular phylogeny suggested that CiOX is divergent from ATRs and human orexin receptors (hOX). However, CiOX appears closer to hOX than to ATR both in terms of sequence percent identity and in its modelled binding cavity, as suggested by molecular modelling. CiOX was heterologously expressed in a recombinant HEK293 cell system. Human orexins weakly but concentration-dependently activated its G signalling (Ca elevation), and the responses were inhibited by the non-selective orexin receptor antagonists TCS 1102 and almorexant, but only weakly by the OX-selective antagonist SB-334867. Furthermore, the 5-/6-carboxytetramethylrhodamine (TAMRA)-labelled human orexin-A was able to bind to CiOX. Database mining was used to predict a potential endogenous C. intestinalis orexin peptide (Ci-orexin-A). Ci-orexin-A was able to displace TAMRA-orexin-A, but not to induce any calcium response at the CiOX. Consequently, we suggested that the orexin signalling system is conserved in Ciona intestinalis, although the relevant peptide-receptor interaction was not fully elucidated.
被囊动物是连接脊椎动物和无脊椎动物之间的进化模式生物。在海鞘（CiOX）中发现的一个基因组序列与脊椎动物食欲素受体和原肠胚神经肽 AT 受体（ATR）具有高度相似性。分子系统发育表明，CiOX 与 ATR 和人类食欲素受体（hOX）不同。然而，分子建模表明，CiOX 在序列百分比同一性和模拟结合腔方面，与 hOX 比与 ATR 更接近。CiOX 在重组 HEK293 细胞系统中进行了异源表达。人类食欲素微弱但浓度依赖性地激活其 G 信号（Ca 升高），并且该反应被非选择性食欲素受体拮抗剂 TCS 1102 和 almorexant 抑制，但被选择性 OX 拮抗剂 SB-334867 仅微弱抑制。此外，5-/6-羧基四甲基罗丹明（TAMRA）标记的人类食欲素-A 能够与 CiOX 结合。数据库挖掘用于预测潜在的内源性海鞘食欲素肽（Ci-orexin-A）。Ci-orexin-A 能够置换 TAMRA-食欲素-A，但不能在 CiOX 诱导任何钙反应。因此，我们认为，尽管尚未完全阐明相关的肽-受体相互作用，但在海鞘中，食欲素信号系统是保守的。
