Expression of Dp71 in Muller glial cells: A comparison with utrophin- and dystrophin-associated proteins

PURPOSE. The abnormal retinal electrophysiology observed in patients with D uchenne muscular dystrophy (DMD) has been attributed to atl altered express ion of C-terminal products of the dystrophin gene. It has been shown that D p260 is expressed by photoreceptor cells, whereas Dp71 is present in glial cells. The present study was intended to identify all known members of the dystrophin superfamily and their associated proteins expressed in Muller gl ial cells (MGC). METHODS. The expression of the proteins and of their messengers was studied in MGC cultures from 2-week-old rats, by polymerase chain reaction amplifi cation, Western blot analysis, and immunocytochemistry. An immunocytochemic al localization of the proteins was also performed on enzy- matically disso ciated Muller cells from adult rat retinas. RESULTS. MGCs expressed a spliced isoform of Dp71 called Dp71f, as well as utrophin, beta-dystroglycan, delta and gamma-sarcoglycans, and alpha 1-synt rophin. In morphologically preserved differentiated Muller cells, Dp71f was localized in clusters, utrophin mas diffusely distributed in the cytoplasm , and dystrophin-associated proteins (DAPs) were membrane-bound. Most of th ese proteins were preferentially expressed in the vitread portion of the ce lls. Dp71f and utrophin expression was restricted to MGCs, whereas all DAPs were also present in other retinal cell types. CONCLUSIONS. The exclusive localization of Dp71f and utrophin in MGCs sugge sts that these proteins, together with DAPs, play a specific role in these cells. Further knowledge of possible interactions of these proteins within a functional complex may provide new insights into the molecular basis of t he electroretinogram phenotype with DMD.