Collagen type I and type V are present in the same fibril in the avian corneal stroma.

Abstract

Abstract. The distribution, supramolecular form, and arrangement of collagen types I and V in the chicken embryo corneal stroma were studied using electron microscopy, collagen type-specific monoclonal antibodies, and a preembedding immunogold method. Double-label immunoelectron microscopy with colloidal gold-tagged monoclonal antibodies was used to simultaneously localize collagen type I and type V within the chick corneal stroma. The results definitively demonstrate, for the first time, that both collagens are codistributed within the same fibril. Type I collagen was localized to striated fibrils throughout the corneal stroma homogeneously. Type V collagen could be localized only after pretreatment of the tissue to partially disrupt collagen fibril structure. After such pretreatments the type V collagen was found in regions where fibrils were partially dissociated and not in regions where fibril structure was intact. When pretreated tissues were double labeled with antibodies against types I and V collagen coupled to different size gold particles, the two collagens colocalized in areas where fibril structure was partially disrupted. Antibodies against type IV collagen were used as a control and were nonreactive with fibrils. These results indicate that collagen types I and V are assembled together within single fibrils in the corneal stroma such that the interaction of these collagen types within heterotypic fibrils masks the epitopes on the type V collagen molecule. One consequence of the formation of such heterotypic fibrils may be the regulation of corneal fibril diameter, a condition essential for corneal transparency.T HE structure of collagen fibrils, the grouping of fibrils into bundles, and the organization of fibril bundles within the stroma are all important in the determination of extracellular matrix structure and function. The corneal stroma is a highly organized connective tissue in which the rigid control of fibril diameter and the precise arrangement of the collagen fibrils is essential for optical transparency (9). Corneal collagen fibrils have a monotony of small diameter fibrils (•25 nm) with a constant center to center spacing. The fibrils are further organized into orthogonal lamellae (3, 18-20, 45, 46). This uniformity and order at all levels of matrix architecture makes the corneal stroma an ideal tissue for studies on the in situ regulation of collagen fibrillogenesis.Collagen fibril formation is a complex process that is regulated by a number of different factors, including: the collagen type or types present (2, 37), the sequence and extent of propeptide processing (14,15,38), interactions with other matrix components (7, 41), as well as a direct involvement of the cells (3,4,45). The collagen composition, distribution of collagen types, and fibril organization are characteristic of different connective tissues. The earliest corneal anlagen in the embryonic chicken is the primary stroma, an acellular orthogonal fibrillar meshwork composed of collagen types I and II, produced by the co...

Localization of pro‐α2(V) collagen transcripts in the tissues of the developing mouse embryo

“…In conclusion, this study demonstrates that the developmental expression of co15a2 coincides in most instances with that of type I collagen, thus emphasizing the close functional relationship between these two collagen types (Birk et al, 1988(Birk et al, , 1990. This work also provides a much needed background for the future interpretation of phenotypes resulting from the targeting of the mouse gene, as well as for the analysis of collagen regulation in transgenic mice.…”

“…In contrast, very little is known about the function and thus the potential pathogenic contribution of the minor fibrillar collagens (types V and XI). Experimental evidence suggests that types V and XI may regulate the growth and orientation of type I and 11 fibrils in non-cartilaginous and cartilaginous tissues, respectively (Birk et al, 1988(Birk et al, , 1990Mendler et al, 1989;Adachi et al, 1989). It is, therefore, conceivable that metabolic dysfunctions of these minor collagens may influence fibrillogenesis and, therefore, impact upon animal morphogenesis.…”

Collagen fibril assembly during postnatal development and dysfunctional regulation in the lumican‐deficient murine cornea

“…Type I collagen is the most prevalent form and type V collagen comprises 10 -20% of the total corneal fibrillar collagen. These collagens co-assemble into heterotypic fibrils (Birk et al, 1988(Birk et al, , 1990. The keratocytes also produce at least 4 different small leucinerich proteoglycans: decorin, lumican, keratocan, and osteoglycin (Hassell et al, 1983;Blochberger et al, 1992;Funderburgh et al, 1997;Beales et al, 1999;Dunlevy et al, 2000).…”

Homozygosity and Heterozygosity for Null Col5a2 Alleles Produce Embryonic Lethality and a Novel Classic Ehlers-Danlos Syndrome–Related Phenotype

“…Collagen V is a low-abundance fibrillar collagen widely distributed in vertebrate tissues as a1(V) 2 a2(V) heterotrimers, 1 which are incorporated into growing fibrils with the more abundant collagen I and involved in regulating the geometry and tensile strength of the resulting collagen I/V heterotypic fibrils. 2,3 Mutations in the genes encoding either the a1(V) 4 or a2(V) 5 chain can result in the human heritable connective tissue disorder classic Ehlers-Danlos syndrome (cEDS), clinical hallmarks of which include skin hyperextensibility, atrophic scarring, and joint hypermobility, with patients also often presenting with easy bruising and bleeding. 6 At the molecular level, the collagen fibrils of cEDS skin have variability in diameter not seen in normal skin and include large diameter collagen fibril aggregates with abnormal cauliflower-like shapes when viewed in cross section.…”

“…2,3 Mutations in the genes encoding either the a1(V) 4 or a2(V) 5 chain can result in the human heritable connective tissue disorder classic Ehlers-Danlos syndrome (cEDS), clinical hallmarks of which include skin hyperextensibility, atrophic scarring, and joint hypermobility, with patients also often presenting with easy bruising and bleeding. 6 At the molecular level, the collagen fibrils of cEDS skin have variability in diameter not seen in normal skin and include large diameter collagen fibril aggregates with abnormal cauliflower-like shapes when viewed in cross section.…”