Histochemical localization of hyaluronic acid in vitreous during embryonic development.

PURPOSE To determine the chronology of the appearance and localization of hyaluronic acid (HA) in mouse vitreous during the embryonic and early postnatal stages of development and in human vitreous during early embryonic development. METHODS A histochemical method using the specific affinity for HA of a bovine cartilage proteoglycan was used on mouse eyes at embryonic (11 to 18 days) and early postnatal (8 and 18 days) stages. The same technique was applied to human embryonic eyes of 6, 8, 9, and 10 weeks. RESULTS In the mouse, HA is detected early (12-day embryo stage) in the equatorial vitreous and in the internal portion of the corresponding retinal epithelium, behind the anterior rim of the optic cup. Later in development, HA staining extends temporarily to the posterior vitreous and to the internal layers of the posterior retinal epithelium. In human embryos, HA staining is clearly visible in the posterior vitreous and in the equatorial vitreous, where it is more intense at all the developmental stages. From the 8-week stage onward, the internal layers of the developing retina are also heavily stained. CONCLUSIONS HA appears very early in developing vitreous of mice and humans, and staining is observed first and predominantly in the equatorial portion of the vitreous. In contrast to human embryos, HA staining in the posterior mouse fetal vitreous is only faint and transient. In both species, staining of the internal layers of the retinal epithelium is detected in the presumptive ciliary body region and in the more posterior retina. The observed temporal and regional simultaneous localization of HA staining in the vitreous and the internal layers of the retinal epithelium is suggestive of a possible role for these cells in the production of the molecule.