Novel reptilian uncoupling proteins: molecular evolution and gene expression during cold acclimation

Area of Science:

• Biochemistry
• Evolutionary Biology
• Physiology

Background:

• Animals often increase metabolism in cold, risking oxidative damage.
• Uncoupling proteins (UCPs) mitigate this by increasing proton conductance in mitochondria.
• Reptilian UCP gene presence and function in cold adaptation are largely unknown.

Purpose of the Study:

• To investigate the presence of UCP genes in reptiles (Crocodylus porosus).
• To establish the phylogenetic context of reptilian UCP genes.
• To examine UCP gene expression changes during cold acclimation in crocodiles.

Main Methods:

• Gene identification and sequencing in crocodiles.
• Phylogenetic analysis of UCP genes.
• Quantitative PCR to measure UCP gene expression in liver and muscle tissues under varying temperatures.

Main Results:

• The study provides the first evidence of UCP2 and UCP3 genes in reptiles.
• Crocodile UCP2 and UCP3 are expressed in liver and skeletal muscle.
• Cold acclimation significantly upregulated UCP2 and UCP3 expression in crocodile liver, but not muscle.
• Two UCP3 transcripts were identified, one yielding a truncated protein lacking a regulatory domain.
• Molecular phylogeny indicates UCP1 is ancestral and lost in archosaurs; reptilian UCP3 may have evolved functions similar to mammalian UCP1.

Conclusions:

• Reptiles possess UCP2 and UCP3 genes, with distinct expression patterns in crocodiles.
• UCP gene expression in crocodile liver is responsive to cold acclimation, indicating a role in thermoregulation.
• The evolution of UCP genes in vertebrates, particularly the potential functional replacement of UCP1 by UCP3 in birds, offers insights into endothermy.