Genetic differences of DNA and RNA synthesis in the epithelium of the lens of the chick

Ageing in the chick lens: in vitro studies

In principle, ageing may be due to the interaction of several factors, including the accumulation of random changes both genomic and non-genomic, secondary changes in a tissue contingent upon the changing function of other tissues, and programmed non-random changes in the tissue-specific expression of various genes. The use of a single tissue comprising one cell type only, in which the major gene products are well defined, in which there is a well attested series of developmental and age-related changes in cell properties and gene expression and which can be studied and compared in vivo and in vitro, offers advantages for investigation of these questions. The vertebrate eye lens possesses these advantages. The crystallins (proteins expressed at super-abundant levels in the lens) are well characterised. The lens epithelial cells (LEC) grow readily and can differentiate into the lens fibre cells in vitro, and, finally, such terminally differentiated cells may also be derived, by a process of transdifferentiation, from neural retina cells (NRC) in vitro. Thus the effect on ageing changes of the tissue of origin may also be studied. This article reviews our previous studies on long-term changes in growth potential, differentiation capacity and crystallin expression of chick lens cells in ageing cultures, their overall similarity to events in vivo and the effect on ageing changes of genotypes affecting the growth rate. It presents new information on these genetic aspects, and on crystallin expression in long-term ageing cultures of transdifferentiated neural retina, and compares the behaviour of ageing chick lens cells with that reported for mammals.

The influence of the genotype on the process of ageing of chick lens cells in vitro

We reported previously that changes in crystallin expression in differentiating long-term primary cultures of lens cells from five different chick genotypes are similar to those which occur in vivo between hatching and the 8-week-old adult. These changes followed a similar program in all genotypes but occurred more rapidly in cells from the fast-growing than from the slow-growing genotypes. The present study examines ageing changes in lens cell populations from the same five genotypes, over a 4-6 month period, using long-term serial subcultures. The capacity for lentoid differentiation was progressively lost, but the rate of loss was inversely related to the intrinsic growth rate of the cells of these genotypes, occurring at the first passage in the slowest-growing strain, while fifth passage cells of the fastest-growing strain still retained some lentoid-forming capacity. The rate of loss of crystallin expression was also inversely related to the genetic growth rate, but the sequence of changes appears to be nonrandom, since it was broadly similar in all genotypes, starting with a preferential loss of delta-crystallin, as occurs in vivo; although alpha- and beta-crystallins were undetectable in late dedifferentiated cultures, the capacity of the cells for their synthesis was still present. Cultures from both fast-growing genotypes eventually showed senescence, but those from all three slow-growing genotypes underwent transformation. The major cell component in late cultures of all genotypes was actin.

Patterns of crystallin expression during differentiation in vitro of several chick genotypes with different effects on lens cell growth rate

We have recently reported that chick lens cells during differentiation in long-term culture show a programme of change in crystallin expression which mimics events during lens development in vivo. The aim of the present work was to examine the stability of the programme by testing the response to genetic influences and exposure to a carcinogen. Five genetically distinct inbred strains of chick, differing in the intrinsic growth rates of lens epithelial cells in vitro, were used to study the effects of the rate of mitosis on crystallin expression, both during lens development and in long-term cell culture. The time of appearance of lentoids, their size and abundance and the rate of change in crystallin expression were all modified in a genotype-specific way, related to the rate of mitosis, but the programme of changes in crystallin expression was the same for all genotypes. Genetic differences were also found in the patterns of response to treatment of cultures during the logarithmic growth phase with a nitrosoguanidine compound known to affect cell differentiation in lens cultures and several other systems. The changes in crystallin expression and fibre differentiation were delayed, but cultures of the faster growing genotypes were least affected. With further culture, crystallin expression tended to recover to control values although levels of fibre differentiation and cell growth remained depressed. The results indicate that genetic differences in intrinsic growth rate moderate but do not change the programme of crystallin expression shown by lens epithelial cells in culture, and that this programme shows resistance to change.

Comparative studies of normal and genetically hyperplastic lens epithelia II: lectin-induced cell agglutination and 125I-lectin uptake by cells

The reactions of lectins with dissociated and cultured epithelial cells from hyperplastic lenses of two unrelated chick strains, Hy-1 and Hy-2, characterised by hyperplasia of the lens epithelium, and lenses of a normal genotype (N) were investigated using four different lectins. Three methods of monitoring lectin-binding to cell surfaces were employed. Each of the four lectins used showed an individual pattern of reactivity to separated membrane components. Data obtained with the three labelling methods showed the same trend viz: increased agglutinability and high affinity for binding of all four lectins by Hy-1 and Hy-2 cells. These results suggest that Hy-1 and Hy-2 lens epithelial cells are characterised by alteration in their cell surfaces.