Exposure of rod outer segments to serum is not responsible for abnormal disk membrane morphogenesis in a model of retinal detachment

The sclerad surface of the retina is exposed to serum proteins in several retinal pathologies that result in degeneration of photoreceptor outer segments. Abnormal disk membrane morphogenesis is observed in rod photoreceptors of detached Xenopus retinas when they are cultured in serum-containing medium. Retinas that remain attached to the pigment epithelium layer produce normal disks. Experiments were conducted to determine whether abnormal disk morphogenesis in detached, cultured retinas is due to the presence of serum in the microenvironment of the rod outer segments.

Detached retinas and retinas attached to the retinal pigment epithelium in eyecups were cultured in either serum-containing or serum-free medium, and the morphology of the disk lamellae formed in vitro retinas was evaluated. Using protein extraction and immunochemical methods, the presence of albumin in the microenvironment of the outer segments was confirmed for retinas incubated in serum-containing medium.

There were no obvious differences in the abnormal disk-like lamellae formed in detached retinas when the retinas were incubated either in serum-containing or in serum-free culture medium. Proteins extracted from detached retinas cultured in serum-containing medium showed a prominent band at 63 kDa that co-localized primarily with outer segment-enriched fractions. Immunolabeling showed that the band was serum albumin.

Rod cells in detached retinas formed abnormal disk-like lamellar membranes in either serum-containing or serum-free medium. This suggests that exposing outer segments to serum albumin or other serum components is not responsible for the abnormal in vitro disk membrane morphogenesis seen in detached retinas.