Decorin expression during development of bovine skeletal muscle and its role in morphogenesis of the intramuscular connective tissue

Decorin is a small leucine-rich proteoglycan suspected of playing an important role in tissue morphogenesis. However, its role in the development of skeletal muscle is less clear. In the present study, the expression and spatial distribution of decorin in developing skeletal muscle of bovine fetuses were investigated, in order to provide a background for understanding the function of decorin in morphogenesis of the intramuscular connective tissue that supports muscle fibres. Western blot analysis showed that decorin already existed in skeletal muscle by 2.5 months of fetal development, and that decorin had a longer glycosaminoglycan chain in the early fetal stages than in later development, but its core protein was of the same size. Decorin mRNA was expressed at 1 month of fetal development, although its level was relatively low. Indirect immunofluorescence microscopy demonstrated that decorin was located in the perimysium which consisted of collagen fibres, but not in the endomysium which was composed of collagen fibril networks in fetal skeletal muscle. The relatively integrated structure of the perimysium had already formed by 2.5 months of fetal development, when muscle fibres were not tightly assembled and the surrounding endomysium was not well organized. These results suggest that decorin contributes to the formation and stabilization of collagen fibres in the perimysium that support muscle fibres assembled with myogenesis.