Retention and tissue-specific expression of uncoupling protein homoeologs in Xenopus laevis

Mitochondrial uncoupling proteins (UCPs) play central roles in vertebrate energy metabolism, with UCP1 specializing as a thermogenic effector in placental mammals. Comparative genomics demonstrated that UCP1, UCP2, and UCP3 originated prior to the emergence of endothermy, suggesting that their ancestral functions evolved in ectothermic vertebrates. Here, we investigated the genomic organization, conserved synteny, and mRNA expression of all three UCP paralogs and homoeologs in the allotetraploid amphibian Xenopus laevis. Comparative genome analyses revealed that all three UCP paralogs and their long (L) and short (S) homoeologs were retained following polyploidization, although local rearrangements were evident for neighboring genes at the UCP2/UCP3 locus. Quantitative expression analyses across adult frog tissues revealed pronounced tissue specificity, with predominant expression of UCP1 and UCP2 in kidney, UCP3 in muscle, and differences in UCP2 homoeolog expression levels. Together, these findings establish a framework for UCPs in an amphibian model organism, primarily linking them to energetically demanding tissues.