Correction to: Differentiation of RPE cells from integration-free iPS cells and their cell biological characterization.

The original article [1] contains an error in the legend of Fig 5 whereby the descriptions for panels 5d and 5e are incorrect; as such, the corrected legend can be viewed below with its respective figure images

Cell Culture Analysis of the Phagocytosis of Photoreceptor Outer Segments by Primary Mouse RPE Cells

The phagocytosis of photoreceptor outer segments (POSs) by the retinal pigment epithelium (RPE) is essential for retinal homeostasis. Defects in this process can be caused by mutations in the photoreceptor cells, the RPE cells, or both cell types. This function can be experimentally investigated by performing an in vitro phagocytosis assay, in which cultured RPE cells are challenged with isolated POSs, and subsequently tested for their ability to degrade the POSs. A significant advantage of this approach is that mutant phenotypes can be attributed either to the photoreceptor or the RPE cells, by experimenting with different permutations of mutant and control photoreceptor and RPE cells. In this chapter, we detail the method for a double-immunofluorescence assay for analysis of the binding, ingestion, and subsequent degradation of isolated mouse POSs by cultured mouse primary RPE cells

Microtubule Motor Transport of Organelles in a Specialized Epithelium: The RPE.

The retinal pigment epithelium (RPE) is a uniquely polarized epithelium that lies adjacent to the photoreceptor cells in the retina, and is essential for photoreceptor function and viability. Two major motile organelles present in the RPE are the melanosomes, which are important for absorbing stray light, and phagosomes that result from the phagocytosis of the distal tips of the photoreceptor cilium, known as the photoreceptor outer segment (POS). These organelles are transported along microtubules, aligned with the apical-basal axis of the RPE. Although they undergo a directional migration, the organelles exhibit bidirectional movements, indicating both kinesin and dynein motor function in their transport. Apical melanosome localization requires dynein; it has been suggested that kinesin contribution might be complex with the involvement of more than one type of kinesin. POS phagosomes undergo bidirectional movements; roles of both plus- and minus-end directed motors appear to be important in the efficient degradation of phagosomes. This function is directly related to retinal health, with defects in motor proteins, or in the association of the phagosomes with the motors, resulting in retinal degenerative pathologies