Autophagy in dedifferentiating newt iris epithelial cells in vitro.

The ultrastructure of dedifferentiating iris epithelial cells of adult newts was studied in vitro, under the conditions which allow subsequent conversion into lens cells. The dense population of melanosomes which characterize the normal differentiated cells are progressively lost before the cells convert into lens cells. The loss of melanosomes is accompanied by the appearance of a layer of material of intermediate density surrounding the melanosomes. Subsequently vacuoles of various sizes appear in which melanosomes, ribosomes, and multivesicular bodies are sequestered. Further observations suggest that these affected organelles are destined for exocytosis. The cytochemical test for acid phosphatase is positive in the immediate vicinity of melanosomes, in the melanosome clusters, and in the multivesicular bodies. On the other hand, normal iris epithelial cells in situ are negative to the acid phosphatase test. The results are interpreted to indicate that autophagy and exocytosis of melanosomes and other organelles occur during the dedifferentiation of iris epithelial cells.