This study tested the hypothesis that increased growth in channel catfish is associated
with expression of the genes that code for uncoupling proteins (UCP) 2 and 3, members of
the mitochondrial channel proteins involved in nutrient sensing and metabolism. The
specific objective was to contrast the levels of UCP2 messenger RNA (mRNA) in fast vs slow
growing catfish as well as in fed vs fasted catfish. Two distinct UCP2 transcripts were
identified and named UCP2a and UCP2b, respectively. Nucleotide and amino acid sequence
of catfish UCP2s were highly similar to UCP2 and other UCPs from other fish and mammals
(>75%). Expression of UCP2a mRNA was detectable at very low levels in various metabolically
active tissues, whereas the expression of UCP2b mRNA was readily detectable in
the muscle and heart. In a 21-wk feeding study, fish that grew faster had a greater percent
body fat at the end of the study (P < 0.01). Expression of UCP2b mRNA tended to be lower
(P < 0.10) in fast growing fish in the middle of the study although levels were similar at the
beginning and the end of the study. In the fed vs fasted study, expression of UCP2b mRNA
in muscle was increased (P < 0.05) in fish assigned to 30 d of fasting. Our results suggest
that, based on the nucleotide and amino acid sequence similarities and tissue mRNA
distribution, catfish UCP2b may be the analog to UCP3. Moreover, our results suggest selection
toward growth and associated fat accumulation appears to be independent of
muscle UCP2b mRNA expression and UCP2b-mediated mechanisms