Collagen biosynthesis during connective tissue development in chick embryo

Abstract

At various stages of embryonic development, chick embryos were pulse-labeled with radioactive proline and protein was isolated from either whole embryo or specific tissues. The protein was digested with purified, protease-free bacterial collagenase to specifically cleave collagen into trichloroacetic acid soluble peptides. The relative rate of collagen synthesis was determined by comparison of the amount of radioactivity incorporated into collagen and noncollagen protein. Such determinations in the intact embryo revealed a 6-fold increase in the relative rate of collagen synthesis between 6 and 12 days of development. When isolated tissues were analyzed, the relative rate of collagen synthesis was found to increase 2.2-fold in the frontal bone between 11 and 14 days and 5.4-fold in the lower limb between 8 and 14 days; it remained relatively constant in skin between 8 and 16 days. The rate of calcification began to increase after the maximal rate of collagen synthesis had been reached in both bone tissues. The specific activity of alkaline phosphatase was at a high level at 11 days in the frontal bone and increased parallel to collagen synthesis. In bones of the lower limb, the specific activity of this enzyme increased almost in parallel to the rate of calcification. The results suggest that increased collagen synthesis is a prerequisite for bone formation, but the significance of the developmental pattern of alkaline phosphatase in this process is unclear.