SDF-1α mRNA in BCCs and BM stroma at different coculture confluence. Cocultures were added established with 100 cells each and at different confluency; each cell subset was separated and then studied for SDF-1 mRNA by Northern analyses. Normalized bands are presented as the mean densities ± SD for P3, P4, T47D, and DU4475. Each BCC was studied with BM stroma from a different donor. The x-axis shows the confluence (%) and also the average time to attain the respective confluence. Zero confluence indicates the time of coculture initiation. Northern analyses at 0% confluence (time 0) showed the values of BCCs and stroma as cells that have never been placed in coculture. To prevent overlap of bands, we arbitrarily assigned densities of 5 and 3 for confluent BCCs and BM stroma cultured alone, respectively.