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Collagen fibril assembly in the developing avian primary corneal stroma
J M Fitch1, C M Linsenmayer, T F Linsenmayer
1Department of Anatomy and Cellular Biology, Tufts University Medical School, Boston, Massachusetts 02111.
Investigative Ophthalmology & Visual Science
|March 1, 1994
Summary
Avian cornea collagen types II and IX are synthesized by the epithelium and assemble into fibrils shortly after secretion. Maturation involves cross-linking and masking of epitopes, with type IX becoming fibril-associated and type II epitopes degrading later.
Area of Science:
- Developmental Biology
- Extracellular Matrix Research
- Ophthalmology
Background:
- The avian cornea's primary stroma is an organized extracellular matrix rich in collagen fibrils.
- These fibrils are heterotypic, containing collagen types I, II, and IX.
- Epithelial secretion of matrix components offers a model for studying collagen fibril assembly.
Purpose of the Study:
- To determine the timing and location of collagen types II and IX assembly into fibrils in the developing avian cornea.
- To investigate the maturation process of heterotypic collagen fibrils.
Main Methods:
- Immunofluorescence histochemistry on developing chicken embryo corneas.
- Use of monoclonal antibodies specific to immature (non-cross-linked) collagen types II and IX.
- Pretreatments to inhibit collagen cross-linking and enzymatic digestion with collagenase.
Main Results:
- Immature collagen types II and IX were localized to the subepithelial zone in early corneas.
- Masked epitopes in deeper stromal layers were exposed by inhibiting cross-linking.
- Type IX collagen was undetectable in later stages; type II epitopes showed limited unmasking, suggesting degradation.
Conclusions:
- Corneal type II and IX collagens are epithelium-derived.
- Fibril assembly, including type IX incorporation and cross-linking, occurs rapidly post-secretion.
- Type II collagen's N-telopeptide epitope is masked during development and may be proteolytically degraded during remodeling.