Change in embryonic eye size and retinal cell proliferation following intravitreal injection of glycosaminoglycans.

The vitreous body (VB) is a transparent, extracellular matrix structure that fills the vitreous cavity of the eye. Major constituents of the VB are hyaluronic acid (HA) and glycosaminoglycans (GAGs), both of which are highly charged, linear carbohydrate polymers. The present experiments investigate a possible role of HA and GAGs in regulating eye size during development and investigate whether changes in eye size are synchronized with cell proliferation in the retina. Chondroitin sulfate (CS), heparan sulfate (HS), heparin (Hep), dextran sulfate (DexS), and HA were injected into the vitreous cavity of embryonic day 5 chick embryos. Eye size was assessed 1 to 5 days after the injections. Cell counts and BrdU labeling established whether changes in eye size were paralleled by an increase or a decrease in retinal cell proliferation. Injection of CS and HS led to an increase in eye size that was accompanied by a similar increase in retinal cell numbers. Hep and DexS injections led to a decrease in eye size that had no impact on cell proliferation in the retina. HA application had no effect on eye size. The changes in eye size after intravitreal application of GAGs demonstrate that the composition of the VB can play an important role in the regulation of eye size during embryogenesis. The fact that retinal cell proliferation is elevated after an increase in eye size indicates a regulatory role of eye size for retinal cell numbers.