Figure 2.

(A and B) Phase-contrast photomicrographs of layer 6 explants on a homogeneous membrane carpet prepared from layer 6 (target layer; A) and from layer 5 (nontarget layer; B). The two explants extend a comparable number of axons; however, axons form more branches on membranes from target layer than on membranes from nontarget layer. (C and D) Micrographs from membrane stripe assays with layer 6 explants. (C) Stripes of heat-inactivated layer 5 membranes (subscript h) and native layer 6 membranes. When growing parallel to the stripes, axons grow almost exclusively on the native membranes from layer 6. (D) Axons extending perpendicular to alternating stripes of membranes from layer 6 and layer 5 and arborizing preferentially on their target membranes. In each case, membranes isolated from layer 6 are marked with fluorescent beads, as shown on the right of each panel. (Scale bars: 50 μm in A–C and 25 μm in D.)