ARS | Publication request: Identification of two uncoupling protein 2 mRNA in channel catfish: their tissue distribution and changes in their expression after prolonged fasting and refeeding

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 3, 2010
Publication Date: N/A

Technical Abstract: Muscle growth in fish is regulated by complex interactions of neural and endocrine factors that regulate food intake and factors that regulate muscle nutrient metabolism. Our previous studies showed that channel catfish selected for increased growth consumed more food than those with slower growth. However, whether selection of fish for increased growth rate alters muscle nutrient metabolism is largely unknown. Uncoupling proteins (UCPs) regulate the flow of hydrogen ions within mitochondria. Thus far, three distinct UCPs have been identified in mammals and fish, and UCPs have been implicated in both thermogenesis and nutrient metabolism in mammals. However, the physiological role of UCPs in fish is unclear. The gene that encodes UCP2 has been cloned in various fish species including rainbow trout, common carp, and zebrafish. Our objectives were to identify the gene that encodes UCP2 in channel catfish and examine gene expression specificity, as well as the relationship between gene expression and food intake. Comparison of UCP2 mRNA sequences of zebrafish with a channel catfish expression tag sequence library revealed two distinct UCP2 mRNA species (UCP2A and UCP2B). Protein sequence analysis revealed that two UCP2 transcripts were highly similar to each other (75 %). Catfish UCP2 transcripts were also highly similar to UCP2 from other fish and mammals at both DNA (>75 %) and protein (>90 %) levels. Both UCP2 mRNA transcripts were expressed in various tissues; however, expression of UCP2B mRNA was the highest in skeletal muscle, whereas the expression of UCP2A mRNA was high in the digestive organs. We then examined whether changes in food intake affected expression of UCP2A and UCP2B mRNA in muscle of channel catfish. Juvenile channel catfish (n=27) were randomly assigned to one of three groups: fed-control, fasted, or fasted-refed. Fish assigned to the fed-control received food daily for 45 days, whereas fish assigned to the fasted group did not receive food during the experiment. Fish assigned to the fasted-refed group did not receive food for the first 30 days of treatment but were fed daily for 15 days thereafter. Expression of UCP2A mRNA in muscle was similar among all treatments. In contrast, expression of UCP2B mRNA was significantly elevated in the muscle of fasted fish (p<0.05). Expression of UCP2B mRNA in muscle decreased to a level similar to that of control after 15 days of refeeding. The results of our study demonstrated that within the muscle of channel catfish, changes in food intake modified expression of UCP2B mRNA but not UCP2A mRNA. Further studies are required to determine the role of UCP2 in muscle growth and nutrient metabolism, the mechanisms that regulate expression of UCP2 mRNA in muscle of channel catfish, and the use of UCP2 gene expression as a potential genetic marker for selection for increased growth rate.