Stimulatory effects of retinal extract and fibroblast growth factor on lentoidogenesis in cultures of chick embryo neuroretinal cells

A crude extract prepared from embryonic chick retina stimulates growth and particularly transdifferentiation into lens when added as a supplement to neuroretinal (NR) cultures in vitro. This effect is especially marked when using a medium (H) containing 5% horse serum, where growth factors are likely to be limiting. The level of δ-crystallin (lens marker) production in such cultures increases with the concentration of extract. Using extracts from earlier and later stages of retinal development, there is an age-dependent decline in the extent to which transdifferentiation is stimulated. However, such extracts have little effect on the activity of CAT, a neuronal marker enzyme. These effects are most probably mediated by growth factors present in the retinal extract acting upon Müller glial cells or their precursors in the NR cultures. In support of this suggestion, we show that purified fibroblast growth factor (but not epidermal growth factor) exerts similar effects on both culture growth and δ-crystallin accumulation.