Fig. 7.

Quantitation of the effect of Slit2 on the directional growth of retinal axons in vitro.A, Quantitation scheme. Quantitation was done blind to transfected cell type on 13 randomly selected cocultures of each type (those with no outgrowth were not used); 575 axon bundles were analyzed in the cocultures with mock-transfected cells, and 32 axon bundles were analyzed in the slit2-transfected cell cocultures. The axons angle of deviation away from the 293T cells was measured in the “toward” hemiretina sector as follows: a line (Gx), representing the expected direction of growth, was drawn through the center of the explant and the base of the axon bundle. A second line (Ga), representing the actual direction of growth, was then drawn through the base and the tip of the axon bundle. The absolute value of the angle between the base line (thick dashed line) and Ga (AGa) was then subtracted from the absolute value of the angle between the baseline and Gx (AGx). The difference is negative when the bundle extends away from the 293T cells and positive when it extends toward them. B, Retinal axons are not repelled by Slit2 in collagen gel cocultures. No significant difference is found in the angle of deviation of axon bundles away from the 293T cells between the retina mock and the retina Slit2 cocultures (p = 0.22; Student's ttest).