There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
Homeotherms possess various physiological mechanisms to maintain their body temperature,
thus allowing them to adapt to various environments. Under cold conditions, most eutherian
mammals upregulate heat production in brown adipose tissue (BAT), and uncoupling protein
(UCP) 1 is an essential factor in BAT thermogenesis. The evolutionary origin of UCP1
was believed to have been a specific event occurring in eutherian lineages. Recently,
however, the UCP1 ortholog was found in fishes, which uncovers a more ancient origin
of this gene than previously believed. Here we investigate the evolutionary process
of UCP1 by comparative genomic approach. We found that UCP1 evolved rapidly by positive
Darwinian selection in the common ancestor of eutherians, although this gene arose
in the ancestral vertebrate, since the orthologous genes were shared among most of
the vertebrate species. Adaptive evolution occurred after the divergence between eutherians
and marsupials, which is consistent with the fact that BAT has been found only in
eutherians. Our findings indicate that positive Darwinian selection acted on UCP1
contributed to the acquisition of an efficient mechanism for body temperature regulation
in primitive eutherians. Phylogenetic reconstruction of UCP1 with two paralogs (UCP2
and UCP3) among vertebrate species revealed that the gene duplication events which
produced these three genes occurred in the common ancestor of vertebrates much earlier
than the emergence of eutherians. Thus, our data demonstrate that novel gene function
can evolve without de novo gene duplication event.