Cell cycle parameters in dedifferentiating iris epithelial cells.

After lentectomy of the adult newt eye, non-dividing iris epithelial cells re-enter the cell cycle. Some of the iris epithelial cells become completely depigmented while they are in the cell cycle, and then differentiate into lens cells. The remaining iris epithelial cells become partially depigmented in the induced cell cycle, but resynthesize melanosomes and recover the normal state of iris epithelial cells. The two groups of cells are spatially separated within the iris epithelium. The cell cycle parameters of both groups of iris epithelial cells were estimated by a mathematical procedure on a computerized programme from the percentage of labelled mitotic cells as a function of time after peritoneal injection of [3H]methyl-thymidine on day 6 after lentectomy. The total cell cycle time was found significantly shorter in the cell population with complete depigmentation as compared with that with partial depigmentation. Based on these results the possible role of differential cell cycle time in the control of dedifferentiation was discussed. Grafting of unlabelled iris into the optic cavity of host animals injected 6 h beforehand with [3H]methyl-thymidine, followed by a study of radioactivity of iris epithelial cells of the graft demonstrated incorporation at a low level during the whole period of experiment in which the cell cycle parameters were estimated. The data used for the estimation were corrected for the delayed incorporation.