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. 2009 Jan 7:9:4.
doi: 10.1186/1471-2148-9-4.

Molecular evolution of UCP1 and the evolutionary history of mammalian non-shivering thermogenesis

David A Hughes  1 , Martin Jastroch, Mark Stoneking, Martin Klingenspor
Affiliations

Molecular evolution of UCP1 and the evolutionary history of mammalian non-shivering thermogenesis

David A Hughes et al. BMC Evol Biol. .

Abstract

Background: Uncoupling protein 1 (UCP1) is a mitochondrial anion carrier, expressed in brown adipose tissue (BAT) of Eutherians. UCP1 is responsible for uncoupling mitochondrial proton transport from the production of ATP, thereby dissipating heat; it is essential for non-shivering thermogenesis (NST) in mammalian BAT. UCP1 orthologs have been identified in non-Eutherian mammals, fish and amphibians. Yet, UCP1 has a unique function in Eutherians in that it is necessary in the production of heat (NST). As such, this study aims to determine the evolutionary mode of UCP1 in Eutherians, where there is clear evidence of UCP1-dependent NST in BAT.

Results: Models of adaptive evolution through phylogenetic analysis of amino acid sequences by maximum likelihood were implemented to determine the mode of UCP1 protein evolution in Eutherians. An increase in the rate of amino acid substitutions on the branch leading to Eutherians is observed, but is best explained by relaxed constraints, not positive selection. Further, evidence for branch and site heterogeneity in selection pressures, as well as divergent selection pressures between UCP1 and its paralogs (UCP2-3) is observed.

Conclusion: We propose that the unique thermogenic function of UCP1 in Eutherians may be best explained by neutral processes. Along with other evidence, this suggests that the primary biochemical properties of UCP1 may not differ between Eutherians and non-Eutherians.

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Figures

Figure 1
Figure 1
Branch lengths are estimates of the number of substitutions per codon as performed in the M2 model with the Eutherian branch set as the foreground branch. Each lineage is defined with the common name of each species and the three letter species code.
Figure 2
Figure 2
UCP species tree. Thick branches are Eutherian lineages for each respective gene. The values above each Eutherian branch are branch length estimates from the M0 model. Three letter species codes are given at the tip of each lineage. Species names can be found in Supplementary Table 1.
Figure 3
Figure 3
A bar plot of site class probabilities for each codon, represented by amino acids in the figure. Site classifications and their omega estimate are defined in the figure. The protein topology, defined as intermembrane, transmembrane and matrix space protein portions was placed above the barplot. Topology was taken from [56].
See this image and copyright information in PMC

References

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