Upregulation of CD44 expression in the retina during the rds degeneration.

In adult mouse retinas the standard form of the cell surface adhesion/receptor molecule CD44 is localized to Müller cell apical microvilli. In the rds (retinal degeneration slow) mouse, however, CD44 immunolabel is increased and distributed throughout the retina by 3 months postnatal. At present, it is unclear if this labeling pattern is due to the increased expression of standard CD44, the expression of variant CD44 isoforms, or an unmasking of CD44 antigenic sites.

Immunolocalization of CD44 in the dystrophic rat retina.

The distribution of the cell surface adhesion/receptor molecule CD44 was studied in retinas of the Royal College of Surgeons (RCS) rat which exhibits an inherited retinal dystrophy. In this animal model, the retinal pigment epithelium fails to phagocytize shed photoreceptor outer segment material, a membranous debris layer accumulates in the subretinal space and the photoreceptor cells degenerate. Using immunoperoxidase and immunogold labeling, CD44 was localized to Müller cell apical microvilli in normal rat retinas, as noted in other species.

Immunocytochemical colocalization of clusterin in apoptotic photoreceptor cells in retinal degeneration slow rds mutant mouse retinas.

In the rds mutant mouse the photoreceptor cells differentiate normally for the first few postnatal days, with the inner segments projecting an extended cilium. However, outer segments fail to form and only rudimentary disks and opsin-laden vesicles assemble at the tip of the cilium. These are shed into the interphotoreceptor space where they are phagocytosed by the retinal pigment epithelial cells.

Distribution of CD44 in the retina during development and the rds degeneration.

It was previously demonstrated that the 90 kDa cell adhesion molecule CD44 is localized to Müller cell apical microvilli which project into the interphotoreceptor matrix in the adult retina. For the current report, the distribution of CD44 was studied in developing normal BALB/c mouse retinas and in rds mutant mouse retinas of various ages. Using immunoperoxidase techniques, positive label for CD44 was first detected on Müller cell microvilli after 7 days postnatal in BALB/c retinas and the band of label widened as the microvilli elongated and the retina reached maturity.

Immunocytochemical localization of CD44 in the mouse retina.

The transmembrane glycoprotein CD44 is a cell adhesion molecule which has recently been localized in a variety of cell types. It mediates cell attachment to extracellular matrix components and also binds to the actin cytoskeleton within the cell. In this study, the presence and distribution of CD44 in the mouse retina was investigated in order to determine whether this molecule might be important for retinal cell adhesion.