Data from: Here and there, but not everywhere: repeated loss of uncoupling protein 1 in amniotes

Endothermy is an evolutionary innovation in eutherian mammals and birds. In eutherian mammals, UCP1 is a key protein in adaptive nonshivering thermogenesis (NST). Although ucp1 arose early in the vertebrate lineage, the loss of ucp1 was previously documented in several reptile species (including birds). Here we determine that ucp1 was lost at the base of the reptile lineage, as we fail to find ucp1 in every major reptile lineage. Furthermore, though UCP1 plays a key role in mammalian NST, we confirm that pig has lost several exons from ucp1 and conclude that pig is not a sole outlier as the only eutherian mammal lineage to do so. Through similarity searches and synteny analysis, we show that ucp1 has also been lost/pseudogenized in Delphinidae (dolphin, orca) and potentially Xenarthra (sloth, armadillo) and Afrotheria (hyrax). These lineages provide models for investigating alternate mechanisms of thermoregulation and energy metabolism in the absence of functional UCP1. Further, the repeated losses of a functional UCP1 suggest the pervasiveness of NST via UCP1 across the mammalian lineage needs re-evaluation.

恒温性是真兽类哺乳动物与鸟类的一项演化创新。在真兽类哺乳动物体内，解偶联蛋白1（UCP1）是介导自适应非颤抖产热（NST）的关键蛋白。尽管ucp1基因早在脊椎动物谱系中就已起源，但此前已有研究在包括鸟类在内的多种爬行动物物种中记录到ucp1基因的丢失。本研究通过系统分析证实，ucp1基因在爬行动物谱系的基部就已发生丢失——我们在所有主要爬行动物谱系中均未检测到该基因的存在。此外，尽管UCP1在哺乳动物的非颤抖产热过程中发挥关键作用，但本研究证实猪的ucp1基因已丢失了数个外显子，并得出结论：猪并非唯一出现此类基因丢失情况的真兽类哺乳动物谱系。通过同源性搜索与同线性分析，本研究表明：海豚科（海豚、虎鲸）的ucp1基因同样发生了丢失或假基因化，异关节总目（树懒、犰狳）与非洲兽总目（蹄兔）也存在类似的潜在可能。这些谱系可为研究丧失功能性UCP1后的体温调节与能量代谢替代机制提供理想模型。此外，功能性UCP1的多次独立丢失现象提示：跨哺乳动物谱系、依赖UCP1的非颤抖产热机制的普遍性需要重新评估。