Oolon Colluphid
31 Mar 2009, 09:57 AM
BMC Evolutionary Biology 2009; 9: 4.
Molecular evolution of UCP1 and the evolutionary history of mammalian non-shivering thermogenesis
Hughes et al.
Background
Uncoupling protein 1 (UCP1) is a mitochondrial anion [negatively charged ion] carrier, expressed in brown adipose tissue (BAT) of Eutherians ['proper' mammals -- the ones that aren't marsupials and monotremes]. UCP1 is responsible for uncoupling mitochondrial proton transport from the production of ATP [the energy-producing machinery in cells], thereby dissipating heat; it is essential for non-shivering thermogenesis [heat production] (NST) in mammalian BAT.
UCP1 orthologs [same genes] 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.
Molecular evolution of UCP1 and the evolutionary history of mammalian non-shivering thermogenesis
Hughes et al.
Background
Uncoupling protein 1 (UCP1) is a mitochondrial anion [negatively charged ion] carrier, expressed in brown adipose tissue (BAT) of Eutherians ['proper' mammals -- the ones that aren't marsupials and monotremes]. UCP1 is responsible for uncoupling mitochondrial proton transport from the production of ATP [the energy-producing machinery in cells], thereby dissipating heat; it is essential for non-shivering thermogenesis [heat production] (NST) in mammalian BAT.
UCP1 orthologs [same genes] 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.