Differential Expression of MSTN Isoforms in Muscle between Broiler and Layer Chickens

SIMPLE SUMMARY: Increasing the growth rate of food animals with a concomitant increase in muscle yield is a primary goal of animal producers. The identification of factors and a better understanding of the underlying mechanisms of these factors for muscle growth are important if we are to improve meat production in domestic animals. In avian species, MSTN-A has anti-myogenic activities and MSTN-B functions as a pro-myogenic factor. In this study, the expression of the Mstn isoforms and the sizes of myofibers and muscle bundles during development were analyzed in broiler and layer chicken breeds. Although the expression levels of total Mstn were not different between the two breeds, the ratios of Mstn-B to -A were significantly higher in the broilers with muscle hypertrophy and hyperplasia compared to the layers. Further characterizations of the muscle in broilers revealed a greater bundle area but similar fiber number per bundle compared to the layers. Our study demonstrated higher ratios of Mstn-B/-A expression in the muscles of broiler chickens, suggesting that the development of strategies to enhance the expression of Mstn-B will lead to increased muscle growth and poultry production. ABSTRACT: Myostatin (Mstn)-A, the main isoform among Mstn splicing variants, functions as a negative regulator, whereas Mstn-B functions as a positive regulator in muscle development. Because broiler chickens are a fast-growing breed raised for meat production and layer chickens are a slow-growing breed raised for egg production, differences in the expression of Mstn isoforms between the two distinct breeds were analyzed in this study. There was no difference in the expression levels of total Mstn (Mstn-A and -B forms) during embryonic development and at D33 between the two breeds. Interestingly, the ratios of Mstn-B to -A were significantly higher in the broiler compared to the layer at most ages. In pectoralis major muscle (PM) tissue, the cross-sectional area (CSA) of muscle fiber was significantly greater in the broiler. The broiler also showed greater bundle CSA and a similar fiber number per bundle compared to the layer at D5 and D33. These data suggest that the greater bundle CSA with myofiber hypertrophy in the broilers is associated with greater muscle growth. The relationship between the expression of Mstn isoforms and growth rate can be used as a potential genetic marker for the selection of higher muscle growth in chickens.