Abstract
Abstract: :
Purpose: Interphotoreceptor retinoid–binding protein (IRBP) and retinoschisin are two known photoreceptor–secreted proteins. IRBP transports all–trans retinol to the retinal pigment epithelium and is the main soluble component of the interphotoreceptor matrix. On the other hand, retinoschsin interacts with Müller and bipolar cells in the retina to establish cell layer and synaptic architectures, and mutations in the gene that encodes retinoschisin cause X–linked retinoschisis, a degenerative disease of the retina. Within the secretory pathway, microtubule mediation of protein trafficking is known to take place and actin regulation of exocytosis is also well established. We examined if the microtubule and actin cytoskeletons play a role in the secretion of IRBP and retinoschisin. Methods: Whole mouse retinas were cultured overnight in medium containing either colchicine, nocodazole, cytochalasin D or DMSO. The culture media were then harvested and subjected to Western blot analyses using anti–retinoschisin and anti–IRBP antibodies. Results: Our data showed that depolymerizing microtubules with 10 µg/ml of colchicine or 5 µg/ml of nocodazole suppressed IRBP secretion, but had no significant effects on retinoschisin secretion. In contrast, depolymerization of microfilaments with 10 µg/ml cytochalasin D reduced IRBP secretion but enhanced retinoschisin release. Conclusions: These results suggest that cytoskeletons are involved in secretion of IRBP and retinoschisin. Microfilaments probably pose barriers for retinoschisin secretion, thereby their depolymerization may facilitate retinoschisin release. Conversely, the integrity of microtubules and microfilaments is important for IRBP secretion, since depolymerization of these cytoskeletons leads to a reduction in IRBP release.
Keywords: photoreceptors • cytoskeleton • proteins encoded by disease genes