Purpose: To study the expression and localization of myocilin in the developing mouse eye. Myocilin is a 55- to 57-kDa secreted glycoprotein that is mutated in some forms of primary open-angle glaucoma.
Methods: The eyes of NMRI mice were studied from embryonic day (E) 14.5 to postnatal day (P) 21, and at 2-3 months of age. Immunohistochemistry was performed with antibodies against myocilin. The specificity of the antibodies was checked by two-dimensional gel electrophoresis. RNA was isolated from eyes at various ages, and the presence of myocilin mRNA was analyzed by northern blot hybridization.
Results: No immunostaining for myocilin was seen before E16.5. At around E17.5, a distinct positive immunoreactivity of optic nerve axons in the developing nerve fiber layer of the retina was observed. At P5-6, immunostaining appeared in perikarya of optic nerve ganglion cells. In the anterior eye, no immunoreactivity was observed until P10. At P12-14, the cells of the epithelial layers of ciliary body and iris, as well as the cells of the trabecular meshwork and iris stroma, became immunoreactive for myocilin. At that time, positive staining for myocilin was also seen in the corneal endothelium and in keratocytes of the corneal stroma. An essentially similar staining pattern was seen in adult eyes. Northern blot analysis for myocilin mRNA in RNA from developing mouse eyes was negative until P9. At P12, a distinct band was observed. A band with similar mobility, but somewhat more intense, was detected in mRNA from adult mouse eyes 2-3 months of age.
Conclusions: The onset of immunoreactivity for myocilin in the retina occurs in parallel with the maturation of optic nerve ganglion cells. In the anterior eye, the expression of myocilin is associated with the final development of those tissues that are directly involved in aqueous humor dynamics. The presence of myocilin might be important for proper function and structure of mature optic nerve ganglion cells and aqueous humor outflow.