Morphological changes and growth stimulation of Bovine Epithelial Lens cells by a retinal extract in vitro

Abstract

Adult Bovine Epithelial Lens cells (BEL cells) proliferate actively in vitro, acquiring several characteristics of spontaneous transformation. They do not differentiate into lens fibre cells under routine culture conditions but they can undergo a morphological change if treated by dexamethasone, as has been reported by van Venrooij et al. [1]. From adult bovine retina we obtained a saline phosphate buffer soluble extract which induced morphological and growth rate modifications of these cells either in primary cultures or in serially subcultured BEL cells. The morphology of the epithelial cells changes from a polygonal to a spindle shape. Experiments with cycloheximide indicate that this morphological change is protein synthesis dependent. It is inhibited by colchicine, suggesting an important participation of the microtubular apparatus. Cell morphology is reverted when the retinal extract is removed or by treatment with cycloheximide after a certain time lag. Cell proliferation is enhanced: the population doubling time, characteristic of the exponential phase, is conserved longer than in non-treated cultures and the density at confluency is increased. Thymidine uptake determinations have shown that DNA synthesis is increased, both in the presence and in the absence of serum. The morphological change can be uncoupled from cell division. These results do not prove that an endogenous morphogenic factor has been extracted, since differentiation into fibres has yet to be investigated, but they do show that, in vitro, the morphology of epithelial cells can be modified by a retinal extract (RE) and that the latter also contains a potent growth-promoting factor.