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. To further characterize this response, we have studied the expression of CD44 mRNA and protein in rds retinas of different ages. RT-PCR analysis demonstrated one product which represented the message for standard CD44 in adult BALB/c mouse retina and in all ages of rds retinas studied. Upon Southern blotting, this major product was detected along with two minor bands of larger size in all samples. Northern blot analysis demonstrated a major transcript of approximately 4.0 kb and a minor one of 3.0 kb in all BALB/c and rds retinas. By 3 months postnatal in rds retinas, the expression of CD44 message was increased by at least two-fold. Western blot analysis demonstrated the presence of only the standard form of CD44 protein in all BALB/c and rds retinas. An increased amount of this standard CD44 protein was observed in 2, 3, and 6 month rds retinas. Thus, this study demonstrates that the inherited retinal degeneration exhibited by the rds mouse does not cause an altered expression of retinal CD44 isoforms, but does lead to an upregulation in the expression of mRNA and protein for standard CD44.