The effects of growth factors on multicellular spheroids formed by chick embryonic retinal cells.

Retinal cells from chick embryos aged 7.5 days of gestation were cultured for two months in a non-adherent suspension culture dish to study the effects of growth factors and co-culture with retinal pigment epithelial cells on their differentiation. Dissociated retinal cells became cellular aggregates (multicellular spheroids) within a day, and rosettes were formed in the spheroids after 2 days. Ultrastructurally, neurons of the rosettes developed connecting cilia, ellipsoids (accumulation of mitochondria), and external limiting membrane, indicative of their differentiation into photoreceptor cells. Epidermal growth factor enhanced the expression of rhodopsin by rosette-forming neurons, while basic fibroblast growth factor induced the growth of Mueller cells at 4 weeks, and their transdifferentiation into lens-epithelial-like cells at 8 weeks. Co-culture of retinal cells with retinal pigment epithelial cells enhanced the formation of rosettes in spheroids. Multicellular spheroids formed in a dish for suspension culture would provide a convenient in vitro system to examine differentiation and transdifferentiation of the retina.