The development of the nervous system is modulated by both genetic and environmental phenomena. Whereas intrinsic factors undoubtedly play roles in the potential of progenitor cells to differentiate into a given cell type, extrinsic clues are likely to serve as signals for the timing of these differentiative events. The proposed project is designed to examine the effects of environmental factors on a cell's phenotype, particularly the environmental factors present in the extracellular matrix (ECM). Experiments are proposed to identify the distribution, expression, and function of components of the extracellular matrix, in particular, the beta2-containing laminins, during the development of the retina using antibodies and cDNA probes, both in vitro and in vivo. Together, it is anticipated that these lines of investigation should help to define the role of these extracellular matrix molecules in the development of the nervous system.