In vitro assay to test differential substrate affinities of growing axons and migratory cells.

An in vitro assay is presented in which different soluble substrates are arranged in narrow alternating stripes which forces growing axons and migratory cells to choose between them. The usefulness of this assay is exemplified by offering goldfish retinal axons and glial cells of the optic nerve a variety of substrates in stripes. Given a choice between substrates of unequal growth supporting activities axons and migratory cells grow in stripes, thus expressing their preference for one of the substrates. Growth in stripes was observed 1. when a substrate with growth promoting properties was next to one which did not possess these properties, 2. when the growth promoting activity of a substrate applied to both stripes was in one stripe blocked by an antibody, 3. when two different growth promoting substrates were offered.