Polarization of the CXCR-4 receptor in response to presented SDF-1α.

Cells plated at the edge of a stripe of SDF-1α on a uniform field of Fn were fixed and stained for the expression of the SDF-1α receptor, CXCR4.24 Shown are selected sections of a confocal Z-section series through a field of cells at the interface between the SDF-1α–coated Fn stripe (left half) and the Fn alone (right half). Numbers in the lower left of each frame indicate the relative position of the optical section, starting from the basal surface of the cells. The final panel shows an enlargement of a region from the +1.2 μm section in which cells polarized in the direction of overall migration are indicated (arrows). Note that the cells in this field on Fn alone are rounder and thicker than those on SDF-1α–coated Fn, as evidenced by the fact that the former remain in the image at the 1.8- and 2.4-μm sections, whereas most of the latter are no longer detectable. Note also that at the basal surface (0 μm) there is relatively higher staining for CXCR4 on cells on the SDF-1α stripe than on Fn alone.