Data from: Here and there, but not everywhere: the 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. 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 likely 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 nonshivering thermogenesis, 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 loss of an intact, full-length ucp1 has repeatedly occurred in multiple mammalian lineages including 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, these results suggest the pervasiveness of nonshivering thermogenesis via UCP1 across the mammalian lineage needs reevaluation.恒温性（endothermy）是真兽类哺乳动物与鸟类的一项演化创新。在真兽类哺乳动物中，解偶联蛋白1（UCP1）是介导适应性非颤抖性产热的关键蛋白。尽管ucp1基因早在脊椎动物谱系起源初期就已出现，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基因的丢失事件。本研究通过对各主要爬行动物谱系的序列检索未发现ucp1基因，据此推断ucp1基因极有可能在爬行动物谱系的基部就已发生丢失。此外，尽管解偶联蛋白1在哺乳动物非颤抖性产热过程中发挥关键作用，但本研究证实家猪的ucp1基因已丢失了数个外显子（exons），且家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。本研究通过序列相似性检索与同线性分析（synteny analysis）证实，完整全长ucp1基因的丢失事件在多个哺乳动物谱系中反复发生，其中包括海豚科（Delphinidae，即海豚、虎鲸），以及可能存在该情况的异关节总目（Xenarthra，树懒、犰狳）与非洲兽总目（Afrotheria，蹄兔）。这些谱系可为探究功能缺失型UCP1背景下的体温调节与能量代谢替代机制提供理想研究模型。此外，本研究结果表明，学界此前认为UCP1介导的非颤抖性产热在哺乳动物谱系中广泛存在这一观点，亟需重新评估。