Vitreous body collagen. Evidence for a dual origin from the neural retina and hyalocytes.

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Abstract
Two different cell types were shown to synthesize embryonic chick vitreous collagen (vitrosin) at different stages of development. Identification of vitrosin was established by labeling the embryos in ovo with [3H]proline at stages 23 and 28 and separating the extracted vitreous collagen .alpha.-chains by carboxymethylcellulose chromatography. The labeled collagen consisted predominately of .alpha.1 chains, indicating a molecule in the form of a trimer of identical chains designated (.alpha.1)3. The MW of the labeled chains measured approximately 95,000 daltons by molecular sieve chromatography, and contained 41% of their imino acid as 4-hydroxyproline. To establish which eye tissues synthesize vitrosin, the collagens produced in organ culture by the isolated neural retina, lens and vitreous body from stages 26-27, 29-30 and 40 were examined. At the 2 earlier stages, only the neural retina synthesized large quantities of (.alpha.1)3 collagen whereas the lens and the cells within the vitreous body itself synthesized relatively small amounts of collagen characterized by an .alpha.1:.alpha.2 ratio of about 2:1. At stage 40, the cells of the vitreous body itself synthesized the greatest quantities of collagen, which now was predominantly an (.alpha.1)3 type molecule. Stage 40 neural retina and lens synthesized lesser amounts of collagen with an .alpha.1:.alpha.2 ratio of 2 to 3:1. Chick vitrosin thus appears to be synthesized by the neural retina in early embryonic stages, whereas the major contribution derives from cells within the vitreous body in later development.