Temporal dissociation of developmental events in the chick eye under low temperature conditions.

The chick embryonic eye is an excellent model for the study of vertebrate organogenesis. Key events in eye development involve thickening, invagination and cytodifferentiation of the lens primordium. While these events occur successively at different developmental stages, the extent to which these events are temporally related is largely unknown. Here we show that the lens invagination is highly sensitive to temperature. Lowering of incubation temperature to 29°C at embryonic day 2 delayed the onset of invagination of the lens, but not thickening and cytodifferentiation, leading to abnormal protrusion of the eye. The temperature shift also delayed the inward bending of the underlying retinal primordium, even in the absence of the lens. Taken together, our results suggest that lens invagination is initiated independently of thickening and cytodifferentiation, possibly by mechanisms associated with morphogenesis of the primordial retina.