Embryonic Cornea Research Articles

Interaction of epidermal growth factor (EGF) with cultured fibroblasts.

This chapter discusses the interaction of epidermal growth factor (EGF) with cultured fibroblasts. EGF is a single-chain polypeptide containing a total of 53 amino acid residues. All the common amino acids are present except lysine, alanine, and phenylalanine. The molecule contains six half-cystine residues in disulfide bridges. EGF is antigenic and is sensitive to proteolytic digestion. It is heat stable, nondialyzable, and has an isoelectric point at pH 4.6. The chapter also discusses the complete amino acid sequence of EGF and presents the location of the three disulfide bridges. A direct stimulatory effect of EGF on epithelial cell proliferation in vitro has been demonstrated in a number of organ culture systems. These include embryonic skin, embryonic cornea, and mammary gland expiants. The effects of EGF are not species specific; expiants derived from the chick, mouse, and human are responsive. The stimulation of epidermal proliferation in organ cultures of chick embryo skin is dependent upon a number of conditions, among which are the age of the embryo and the presence of dermal cells.

Epithelial collagens and glycosaminoglycans in the embryonic cornea. Macromolecular order and morphogenesis in the basement membrane.

The embryonic corneal epithelium synthesizes both collagen and chondroitin sulfate and excretes them across the basement membrane into the subepithelial space where they assemble into a spiraling orthogonal matrix of fibrils. The assembly of collagen into fibrils is first apparent at the outer face of the basement membrane in a region of ordered chondroitin sulfate molecules. Hyaluronate, another morphogenetically important corneal macromolecule, is produced at these early stages only by the inner endothelium. These correlated biosynthetic and ultrastructural data demonstrate discrete macromolecular products of the two corneal epithelia with differing morphogenetic properties and functions.

Organ culture of chick embryonic cornea

The present investigation demonstrates that the chick embryonic cornea is best maintained with respect to gross appearance and amino acid incorporation into stromal collagen when serum is used as part of a nutrient medium. An examination of other parameters, namely, stability of DNA levels, protein accumulation and histology, give further evidence of the ability of serum to maintain the chick embryonic cornea in culture. Quantitative analysis of the changes found in the cultured corneas show characteristic similarities and differences to the corresponding parameters determined in noncultured corneas. It may be merely fortuitous that the pattern of tracer incorporation for corneal stromal collagen in horse serum cultures follows that seen in noncultured tissue. The discrepancy between incorporation and protein accumulation data is perhaps partially due to collagen breakdown.

Hyaluronate production and removal during corneal development in the chick

Glycosaminoglycan (acid mucopolysaccharide) synthesis was studied during development of the embryonic chick cornea by the introduction of isotopically labeled precursors both in ovo and to excised corneas in culture. Results obtained for both types of preparations were similar. Hyaluronate is the major glycosaminoglycan synthesized by the embryonic cornea between stages 24 and 35, a period during which the primary corneal stroma swells and is invaded by mesenchymal cells. Subsequent to the completion of invasion a rapid decline in incorporation of isotopic precursors into hyaluronate occurs concomitant with an increasing hyaluronidase activity. The hyaluronidase is present primarily between stages 35 and 38, when the cornea begins to dehydrate prior to becoming transparent.

Presence of a non-sulphated glucosaminoglycan in embryonic cornea

An analtical evidence has been obtained for the presence of a non-sulphated glucosaminoglycan in the young embryonic White Leghorn chicken cornea, consisting of nearly equimolar amounts of glucosamine and glucuronic acid. The polysaccharide is supposed to be identical with hyaluronic acid.