Actin in the lens: Changes in actin during differentiation of lens epithelial cells in vivo

Abstract

Proteins of newborn rat lens epithelial and fiber cells, and of fiber-cells of the mature rat lens cortex and lens nucleus were separated in two dimensions on O'Farrell gels. Actin appeared as a relatively major component of the newborn lens epithelial cell protein but as a relatively minor component of the newborn lens fiber cell protein. In the mature lens, actin was present as a minor component of the cortical fiber cell protein, while it was absent in the nuclear cell protein. Isoelectric focusing gels were used to study the distribution of the different forms of actin and the percentage of actin in these gels. By scanning the stained proteins on these gels, the percentage of actin was estimated to be 10·7% of the total protein of the lens epithelial cell in the gel but only 1·1% of the total protein of the newborn fiber cell or the mature lens cortical fiber cell. Furthermore the two species of actin, β- and γ-actin, were identified by their location in relation to added skeletal muscle α-actin and turkey gizzard γ-actin in the gel. In the newborn lens epithelial cell the ratio of β γ actin was 2·2, whereas in the newborn lens fiber cell and in the mature lens cortical fiber cell the ratio of β γ actin was 1·2. Tryptic and chymotryptic digestion of the bands corresponding to actin in the gels was done in order to confirm that the putative β- and γ-actin bands of the lens protein are indeed actin. These results demonstrate that the ratio of the two species of actin changes and the relative percentage of actin declines in going from the epithelium, to the cortex, and to the nucleus of the lens.