Type I Collagen Fibril Assembly
The assembly of type I collagen into fibrillar aggregates has been extensively
studied and involves multiple steps, beinning within the cell where synthesis
occurs in the endoplasmic reticulum (1) and from which secretory products
are packaged in the Golgi apparatus (2) and then excreted by fusion of these
packages (3) into extracellular compartments (4), under cellular control,
where self-assembly and enzymatic
processing, if necessary, occurs. The assembly of the collagen occurs
in the extracellular compartments (4) in typical fibroblasts of skin, tendon
and cornea to form short fibril segments
approximately 25 to 50 microns in length. The fibril segments are then
discharged from the formation compartments into bundle
forming compartments (5,6) where they associate with other such segments
to fuse linearly and laterally to form longer,
thicker, biomechanically competent fibrils within bundles. Proteoglcyans
coat fibril surfaces during this process (6). Cross-linking and molecular
stabilization of the fibrils is a post-depositional event (7).
