In multiple membrane traffic pathways induced in the RPE. This has been achieved by deletion of the Chm/Rep1 gene in pigmented cells, which results in poorly prenylated and consequently partly dysfunctional Rab GTPases, giving rise to multiple trafficking defects. Our demonstration that such trafficking defects can lead to the premature appearance of intracellular deposits of lipofuscin containing granules and melanolipofuscin, and extracellularly, thickening of BrM, and exuberant BLamDs, shows the importance of membrane traffic pathways in the maintenance of RPE health and tissue homeostasis.Loss of Rep1 in the RPE causes Partial Defects in Trafficking Pathways in vivoWe have focussed on two major specialised trafficking pathways in the RPE: the movement of melanosomes 23977191 into the apical processes and the processing of phagocytosed rod outer segments. We have shown that the percentage of melanosomes in the apical processes of the RPE is reduced in the absence of Rep1 in the RPE. The movement of melanosomes into the apical processes is totally dependent on Rab27a function [6,7] and so the small number of melanosomes that do access the apical processes in the absence of Rep1 Tunicamycin custom synthesis demonstrates that some prenylated Rab27a must be present in these cells. Similarly, although phagosome degradation is clearly delayed in the absence of Rep1 in the RPE, the majority of the phagosomes are eventually degraded, suggesting only a partial dysfunction in this pathway. Delayed phagosome degradation could result from delayed phagosome maturation and consequent delivery to the lysosome and/or lysosomal dysfunction. Phagosome maturation in other systems is a process dependent upon multiple Rab proteins that regulate sequential interactions with the endocytic pathway before the final Rab7-dependent fusion with the lysosome [17,18,19,20,21]. The huge and synchronised phagocytic load of the RPE may render it particularly susceptible to changes in function of individual phagosomal or endosomal Rab proteins. In addition, Gordiyenko et al. [10] found compromised lysosomal acidification following Rep1 depletion in cultured RPE cells, suggesting that the degradative capacity of the lysosome may be compromised.Loss of Rep1 Leads to the Premature Accumulation of Features Associated with aging in the RPEChmFlox, Tyr-Cre+ mice exhibited lipofuscin containing granules and cytoplasmic deposits, uneven BI and accumulation of BLamDs and BlinDs within 6 months of age. The accumulation of lipofuscin intracellularly, uneven or (-)-Calyculin A enlarged basal infoldings and extracellular basal deposits are all features of aging in the eye [11,12,22], and we therefore propose that loss of Rep1 specifically in the RPE causes premature accumulation of changes associated with aging in these cells. Which trafficking pathway defects might lead to these aging phenotypes? Although the majority of rhodopsin is eventually degraded in ChmFlox, Tyr-Cre+ mice, delayed phagosome degradation is most likely responsible for the early accumulation of lipofuscin, the mixed vacuoles filled with lipofuscin and lipid droplets and membranes resembling disks from outer segments in ChmFlox, Tyr-Cre+ mice. A delay in degradation of POS, rather thanFigure 5. Quantification of basal laminar deposits. Length of RPE containing BLamDs was measured in 11 ChmFlox, Tyr-Cre+ (black square) and 14 littermate control mice (white square) aged between 5 and 13 months. Graph shows percentage of RPE length containing deposits. Results are.In multiple membrane traffic pathways induced in the RPE. This has been achieved by deletion of the Chm/Rep1 gene in pigmented cells, which results in poorly prenylated and consequently partly dysfunctional Rab GTPases, giving rise to multiple trafficking defects. Our demonstration that such trafficking defects can lead to the premature appearance of intracellular deposits of lipofuscin containing granules and melanolipofuscin, and extracellularly, thickening of BrM, and exuberant BLamDs, shows the importance of membrane traffic pathways in the maintenance of RPE health and tissue homeostasis.Loss of Rep1 in the RPE causes Partial Defects in Trafficking Pathways in vivoWe have focussed on two major specialised trafficking pathways in the RPE: the movement of melanosomes 23977191 into the apical processes and the processing of phagocytosed rod outer segments. We have shown that the percentage of melanosomes in the apical processes of the RPE is reduced in the absence of Rep1 in the RPE. The movement of melanosomes into the apical processes is totally dependent on Rab27a function [6,7] and so the small number of melanosomes that do access the apical processes in the absence of Rep1 demonstrates that some prenylated Rab27a must be present in these cells. Similarly, although phagosome degradation is clearly delayed in the absence of Rep1 in the RPE, the majority of the phagosomes are eventually degraded, suggesting only a partial dysfunction in this pathway. Delayed phagosome degradation could result from delayed phagosome maturation and consequent delivery to the lysosome and/or lysosomal dysfunction. Phagosome maturation in other systems is a process dependent upon multiple Rab proteins that regulate sequential interactions with the endocytic pathway before the final Rab7-dependent fusion with the lysosome [17,18,19,20,21]. The huge and synchronised phagocytic load of the RPE may render it particularly susceptible to changes in function of individual phagosomal or endosomal Rab proteins. In addition, Gordiyenko et al. [10] found compromised lysosomal acidification following Rep1 depletion in cultured RPE cells, suggesting that the degradative capacity of the lysosome may be compromised.Loss of Rep1 Leads to the Premature Accumulation of Features Associated with aging in the RPEChmFlox, Tyr-Cre+ mice exhibited lipofuscin containing granules and cytoplasmic deposits, uneven BI and accumulation of BLamDs and BlinDs within 6 months of age. The accumulation of lipofuscin intracellularly, uneven or enlarged basal infoldings and extracellular basal deposits are all features of aging in the eye [11,12,22], and we therefore propose that loss of Rep1 specifically in the RPE causes premature accumulation of changes associated with aging in these cells. Which trafficking pathway defects might lead to these aging phenotypes? Although the majority of rhodopsin is eventually degraded in ChmFlox, Tyr-Cre+ mice, delayed phagosome degradation is most likely responsible for the early accumulation of lipofuscin, the mixed vacuoles filled with lipofuscin and lipid droplets and membranes resembling disks from outer segments in ChmFlox, Tyr-Cre+ mice. A delay in degradation of POS, rather thanFigure 5. Quantification of basal laminar deposits. Length of RPE containing BLamDs was measured in 11 ChmFlox, Tyr-Cre+ (black square) and 14 littermate control mice (white square) aged between 5 and 13 months. Graph shows percentage of RPE length containing deposits. Results are.