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.

恒温性是真兽亚纲哺乳动物与鸟类的一项进化创新。
在真兽亚纲哺乳动物中，UCP1是适应性非颤抖产热
（NST）的关键蛋白。尽管ucp1在脊椎动物谱系中出现较早，
ucp1的丢失此前已在若干爬行动物物种
（包括鸟类）中有文献记载。本研究确定，ucp1在爬行动物谱系的基部即已丢失，
因为我们未能在所有主要爬行动物谱系中找到ucp1。
此外，尽管UCP1在哺乳动物NST中发挥关键作用，
我们证实猪的ucp1基因已丢失多个外显子，并得出结论：猪并非
唯一丢失该基因的真兽亚纲哺乳动物类群。通过
相似性搜索与共线性分析，我们发现ucp1基因在海豚科
（海豚、虎鲸）中亦已丢失或假基因化，且可能在
异关节总目（树懒、犰狳）与非洲兽总目（蹄兔）中存在同样情况。这些类群为
研究无功能性UCP1时的替代体温调节与能量
代谢机制提供了模型。此外，功能性UCP1的反复丢失
表明，UCP1介导的NST在哺乳动物谱系中的普遍性
有待重新评估。