Meeting Abstract

63.6  Sunday, Jan. 5 14:45  Seasonal Variation in Pectoralis Muscle Myostatin and TLL in Small Birds: A Regulatory Role for Seasonal Phenotypes? SWANSON, DL*; KING, MO; HARMON, E; Univ. of South Dakota; Univ. of South Dakota; Univ. of South Dakota david.swanson@usd.edu

Seasonally variable climates produce seasonal phenotypes in small birds such that winter birds are more cold tolerant and have higher thermogenic capacities. One potential regulator of these seasonal phenotypes is myostatin, a muscle growth inhibitor that may be downregulated under conditions promoting muscle hypertrophy in response to increased energy demands. Few studies have examined a role for myostatin in avian responses to periods of changing energy demands. We examined seasonal changes in flight muscle and heart masses and correlated seasonal changes in myostatin gene expression and protein levels, as well as expression of metalloproteinase myostatin activators TLL-1 and TLL-2 in American goldfinches (Spinus tristis) and black-capped chickadees (Poecile atricapillus). Winter pectoralis and heart masses were significantly greater than in summer for goldfinches. Black-capped chickadees showed no significant seasonal variation in muscle or heart masses, although mass-adjusted pectoralis showed a non-significant trend (P = 0.087) toward higher winter levels. Myostatin expression and protein levels in pectoralis muscles of goldfinches were greater in summer than in winter, although not significantly so (P = 0.058 for protein levels), but expression of both metalloproteinase activators was significantly greater in summer. Pectoralis expression of myostatin and metalloproteinase activators were also higher in summer than in winter for chickadees, although significantly so only for TLL-2. These data suggest that a downregulation of myostatin function in winter, regulated especially by a reduction in myostatin processing, may play a regulatory role in mediating seasonal metabolic phenotypes in small birds.