Characterization of collagen fibril segments from chicken embryo cornea, dermis and tendon.

The cornea, dermis and tendon have extracellular matrix architectures with differences in fibril diameter, packing and organization. An early step in fibril assembly is the formation of a striated fibril of discrete length (segment). Fibril segments were isolated from developing chicken cornea, dermis and tendon by physical disruption and the structure characterized. In all three tissues, intact but relatively short fibril lengths were isolated. These segments were asymmetric, having long (alpha) and short (beta) tapered ends. They were also centrosymmetric with respect to molecular packing. Segments isolated from 12- to 16-day corneas, dermis and tendons had identical structures, but their lengths and diameters were distinct. We propose that the increase in length is, at least in part, the result of lateral associations of adjacent segments. In the developing tendon, there is a rapid increase in length and diameter between day 16 and 17, while in the dermis the increase is more linear with respect to time. In the cornea, the fibril segments grow longer, but their diameters remain constant. Disruption of corneas in phosphate-buffered saline yielded larger diameter segments than seen in situ, while tendon or dermis maintained tissue-specific diameters. When corneas were disrupted in buffers that stabilized the water layer associated with the collagen molecules or containing the corneal proteoglycans, then tissue-specific diameters were maintained. These data suggest differences in the stabilization of segments during growth in tissues where diameter increases versus those where diameter remains constant, and this may be related to collagen-proteoglycan interactions.