Changes in crystallin expression during transdifferentiation and subsequent ageing of embryonic chick neural retina in vitro: comparison with lens epithelium.

We have shown that cultured day-old chick lens epithelial cells undergo changes in crystallin expression during lens fibre (lentoid body) differentiation and ageing in serial subculture which are similar to those found in the adult lens in vivo. Here we have maintained neural retina cells, which transdifferentiate in vitro, for 250 days in serial subculture, in order to determine whether the tissue of origin affects the sequence of changes in crystallin expression and capacity for lentoid body formation both during fibre formation in primary culture and ageing in vitro. Alpha and beta-crystallins were detectable before delta-crystallin in primary cultures of both day-old chick lens epithelium and neural retina from 8-day embryos, but while beta 2 (26 kDa) was detected in pre-lentoid lens epithelial cultures it was not detected until after lentoids formed in neural retina cultures. The relative proportions of the alpha- and beta-crystallin polypeptides were similar in lentoid-rich lens epithelium and neural retina cultures, and both cultures underwent similar changes in serial subculture: a loss of lentoid forming capacity, an early preferential loss of delta-crystallin expression followed by a failure to accumulate first alpha- and then beta-crystallins. The order in which the beta-crystallin polypeptides were lost differed between the cultures. There is evidence for rapid turnover of alpha- and beta-crystallins while actin is the major component expressed in both types of aged cultures. Thus lens and retinal cells show some initial differences in the sequence of crystallin expression in primary cultures and in the eventual characteristics of aged cultures, but during the period beginning with lentoid formation and ending with the onset of senescence, lens cells from either source follow a broadly similar programme of ageing changes which are similar to those which occur during lens ageing in vivo.