Developmentally regulated vitronectin influences cell differentiation, neuron survival and process outgrowth in the developing chicken retina.

Vitronectin is a multifunctional protein involved in the regulation of the immune system and blood coagulation. Here we report that the expression of vitronectin is developmentally regulated in the embryonic retina of the chicken. Vitronectin immunoreactivity was detected in chicken retinas from embryonic day 5, encompassing the cell bodies of most neuroepithelial cells. At this developmental stage, alpha v integrin subunit expression was distributed across the retina, suggesting a ligand/receptor interaction. Expression of both vitronectin and alpha v increased during development and reached a maximum at embryonic day 9, a time when most differentiated neurons grow processes and initiate synapse formation. At this age, vitronectin immunoreactivity appeared to be located predominantly in the fiber and inner plexiform layers of the differentiated stratified retina. alpha v immunoreactivity and mRNA expression was seen associated with all layers formed by differentiated neurons, being most abundant in the ganglion cell and inner nuclear layers. Later in development, levels of vitronectin decreased and immunoreactivity appeared exclusively associated with the fiber layer. In accordance with this pattern of expression, vitronectin as a substrate sustained both proliferation and differentiation of cultured neuroepithelial cells from embryonic day 5 retinas. At later stages, vitronectin supported survival and neurite outgrowth of most differentiated neurons. Our data suggest that vitronectin is a ubiquitous component of the retinal extracellular matrix, serving as a substrate for developmental processes such as proliferation, differentiation of neuron progenitors, cell survival, and axonal and dendritic growth of differentiated neurons.