Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/27/2006
Publication Date: 6/1/2006
Citation: Mohamed, S., Keeney, B., Rexroad III, C.E., Yao, J. 2006. Molecular characterization of fish muscle atrophy and proteolysis associated with spawning. Comparative Biochemistry and Physiology 1(2):227-237. Interpretive Summary: The genetic improvement of rainbow trout for aquaculture production requires understanding physiological processes which occur during the lifecycle of the organism. Severe muscle deterioration is a physiological response to the energetic demands of fish spawning. We measured the activities of genes involved in muscle deterioration in the white muscles of rainbow trout during spawning and post-spawning seasons of gravid fish and compared them to sterile fish. Fertile fish at spawning had less muscle tissue and less muscle protein compared to sterile fish and post-spawning fertile fish. Our results indicate that the cathepsin genes mediate muscle protein catabolism during spawning. Further, our results indicate that rainbow trout depend on muscle proteins and not lipids to fuel gonadal maturation during late stages of spawning.
Technical Abstract: Severe muscle deterioration is a physiological response to the energetic demands of fish spawning. This response represents a suitable model to study mechanisms of muscle degradation in fish where the typical tetra-pod methods, such as muscle unloading, are not applicable. Activities and mRNA accumulations of genes in major proteolytic pathways; cathepsins, calpains and the multi-catalytic proteasome, were measured in the white muscles of rainbow trout (RBT) during spawning and post-spawning seasons of gravid fish for comparisons to sterile fish. Fertile fish at spawning had less muscle tissue and less muscle protein compared to sterile fish and post-spawning fertile fish. Muscle deterioration of the fertile fish during spawning was associated with elevated activities and greater mRNA accumulation of cathepsin-L. Concurrently, cathepsin-D, the calpain regulatory subunit and the proteasome catalytic subunit alpha showed increased accumulation of mRNA without a corresponding increase in enzymatic activity. Additionally, to describe the role of the apoptosis in RBT spawning-induced muscle atrophy, caspase-9 cDNA was identified and molecularly characterized from RBT. During spawning, fertile fish had elevated activity and increased mRNA accumulation of caspase-9 but not caspase-3. The present study indicates that cathepsins mediate protein catabolism of the fish during spawning by a cascade involving activation of the apoptosis mediator, caspase-9, but not the apoptosis executioner, caspase-3.