REORGANIZATION OF ACTIN MICROFILAMENTS AND MICROTUBULES IN REGENERATING RETINAL-PIGMENT EPITHELIUM

Retinal pigment epithelium (RPE) regenerating after experimental damag e in rabbits exhibits major changes in cell shape, polarity and juncti ons-features that depend on the cytoskeleton. This report correlates t hese changes with the redistribution of actin microfilaments and micro tubules, using electron microscopy and confocal laser scanning microsc opy. We compare immature cells with the more mature cells that form th e new epithelial monolayer. Two populations of immature RPE cells are interspersed at the edge of the regenerating RPE sheet. One population of immature cells makes few junctions with their neighbors or the bas ement membrane. They form pseudopodia and exhibit a prominent network of actin microfilaments beneath the plasma membrane. These cells are p robably motile and advance the epithelial sheet. Another population of immature cells contains numerous stress fibers that insert into large basement membrane attachments. The cells make focal adhesions with th eir neighbors, rather than the junctional complexes characteristic of mature RPE cells. These cells are probably not motile and mature into the cells forming the new monolayer-cuboidal cells with numerous basal folds and apical villi and a complete belt of intercellular junctions . Stress fibers are lost as the circumferential bundle associated with the zonula adherens re-forms. Microtubules, which form prominent long itudinal bundles running through the processes of immature cells, take on the meshwork organization characteristic of mature RPE as the imma ture cells differentiate. (C) 1995 Academic Press Limited