GENESIS OF THE FROG RETINAL-PIGMENT EPITHELIUM

To examine cell generation in the frog retinal pigment epithelium (RPE ), representative developmental stages from tail-bud to adulthood rece ived a single injection of [H-3]thymidine. Animals were killed either 24 h or several weeks later; eyes were sectioned and processed by stan dard autoradiographic procedures and viewed by epi-polarised illuminat ion. Tile distribution of [H-3]thymidine-labelled cells indicated that the RPE is formed throughout life, including in adulthood, by cell ad dition at the ciliary margin, matching the pattern for the neural reti na. In addition, a very small number of peripapillary RPE cells underw ent division but only in the adult.