The abnormal retinal neurotransmission observed in Duchenne muscular dystrophy (DMD) patients and in some genotypes of mice lacking dystrophin has been attributed to altered expression of short products of the dystrophin gene. We have investigated the potential role of Dp71, the most abundant C-terminal dystrophin gene product, in retinal electrophysiology. Comparison of the scotopic electroretinograms (ERG) between Dp71-null mice and wild-type (wt) littermates revealed a normal ERG in Dp71-null mice with no significant changes of the b-wave amplitude and kinetics. Analysis of DMD gene products, utrophin and dystrophin-associated proteins (DAPs), showed that Dp71 and utrophin were localized around the blood vessels, in the ganglion cell layer (GCL), and the inner limiting membrane (ILM). Dp71 deficiency was accompanied by an increased level of utrophin and decreased level of beta-dystroglycan localized in the ILM, without any apparent effect on the other DAPs. Dp71 deficiency was also associated with an impaired clustering of two Müller glial cell proteins-the inwardly rectifying potassium channel Kir4.1 and the water pore aquaporin 4 (AQP4). Immunostaining of both proteins decreased around blood vessels and in the ILM of Dp71-null mice, suggesting that Dp71 plays a role in the clustering and/or stabilization of the two proteins. AQP4 and Kir4.1 may also be involved in the regulation of the ischemic process. We found that a transient ischemia resulted in a greater damage in the GCL of mice lacking Dp71 than in wt mice. This finding points at a crucial role played by Dp71 in retinal function.

Dystrophin Dp71 is expressed in all tissues, with the exception of skeletal muscle, and is the main Duchenne muscular dystrophy (DMD) gene product in brain. As full-length dystrophin does in skeletal muscle, Dp71 associates with dystroglycans, sarcoglycans, dystrobrevins, syntrophins, and accessory proteins to form the dystrophin-associated protein complex (DAPC) in non-muscle tissues. Although it has been nearly 20 years since the discovery of Dp71, its study has become relevant only recently due to its direct involvement with the two main DMD non-muscular phenotypes: cognitive impairment and abnormal retinal physiology. In this review, we describe the historical background of Dp71 and the experimental models developed for its study. Additionally, we present and discuss the experimental evidence supporting the participation of Dp71 in different cellular processes, including cell adhesion, water homeostasis, cell division, and nuclear architecture. The functional diversity of Dp71 is attributed to the formation of Dp71-containing DAPC in numerous cell types and different subcellular compartments, including in plasma membrane and nucleus, as well as to the capability of Dp71-containing DAPC to work as the scaffold for proper clustering and anchoring of structural and signaling proteins to the plasma membrane and of nuclear envelope proteins to the inner nuclear membrane.