Cell shape, intracellular pH, and fibroblast growth factor responsiveness during transdifferentiation of retinal pigment epithelium into neuroepithelium in vitro.
In this report we show that some retinal pigment epithelial (RPE) cells, with no expression of neural cell adhesion molecule (N-CAM) (RPEN-CAM-), spontaneously lose pigment and start to express N-CAM in culture. Chick RPE cells normally do not express N-CAM, while the protein is present in chick neural retina. Thus some of the RPE cells in culture started to transdifferentiate into a neuroepithelium (NEN-CAM+). We have measured intracellular pH (pHi) in the RPE cultures and followed its changes in response to basic fibroblast growth factor (bFGF). The depigmented cells protrude above the RPE cell sheet and have a lower resting pHi (approximately 7.05) than the pigmented RPE cells (approximately 7.15). The majority of cells with low resting pHi express N-CAM. The difference in the resting pHi between RPEN-CAM- and NEN-CAM+ cells is not due to the N-CAM expression by NEN-CAM+ cells, as their pHi is the same as the pHi of freshly plated single "round" RPEN-CAM- cells that have not spread yet. NEN-CAM+ cells respond to bFGF with a quick and sustained pHi rise. In contrast, neither the cuboidal RPEN-CAM- cells in a colony centre nor single round RPEN-CAM- cells respond to bFGF with cytoplasmic alkalinization. RPE cells do not proliferate in response to bFGF, while NE cells respond to bFGF with a stimulation of growth. We conclude that bFGF acts not on the fully differentiated RPEN-CAM-, but only on those cells which have already started to transdifferentiate and changed their shape and (or) adhesive status.(ABSTRACT TRUNCATED AT 250 WORDS)
Zhou
Y
Y
Department of Anatomy and Cell Biology, University of Toronto, ON, Canada.
Opas
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M
D000818:Animals; D015816:Cell Adhesion Molecules, Neuronal / Q000096:biosynthesis / Q000378:metabolism; D002454:Cell Differentiation; D002455:Cell Division; D048429:Cell Size; D002642:Chick Embryo; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D005353:Fibronectins / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007797:Laminin / Q000494:pharmacology; D018613:Microscopy, Confocal; D010857:Pigment Epithelium of Eye / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D012160:Retina / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism
D015816:Cell Adhesion Molecules, Neuronal; D005353:Fibronectins; D007797:Laminin; D016222:Fibroblast Growth Factor 2