COLLAGEN FIBRILLOGENESIS IN-SITU - FIBRIL SEGMENTS UNDERGO POSTDEPOSITIONAL MODIFICATIONS RESULTING IN LINEAR AND LATERAL GROWTH DURING MATRIX DEVELOPMENT

Elucidating how collagen fibril growth is regulated is important in de termining how tissues are assembled. Fibrils are deposited as segments , The growth of these segments is an important determinant of tissue a rchitecture, stability, and mechanical attributes. Fibril segments wer e isolated from developing tendons and their structure characterized, The post-depositional changes leading to Linear and lateral growth of fibrils also were examined, Segments extracted from 14-day chicken emb ryo tendons had a mean length of 29 mu m. The segments were asymmetric , having a short and a long tapered end. Most of the segments were cen trosymmetric with respect to molecular packing. Segments extracted fro m 12-to 16-day tendons had the same structure, but mean segment length increased incrementally due to the addition of an increasingly large population of longer segments. At 17 days of development there was a p recipitous increase in segment length, The morphological data indicate that the increase in length was the result of lateral associations am ong adjacent segments, Analysis demonstrated that this fibril growth w as associated with a significant decrease in fibril associated decorin . Using immunoelectron microscopy, decorin was seen to decrease signif icantly at 18 days of development. When decorin content was biochemica lly determined, a decrease also was observed. Decorin mRNA also decrea sed relative to fibrillar collagen mRNA during the same period. These data support the hypothesis that a decrease in fibril-associated decor in is necessary for fibril growth associated with tissue maturation. G rowth through post-depositional fusion allows for appositional and int ercalary growth and would be essential for normal development, growth, and repair. (C) 1995 Wiley-Liss, Inc.