Expression of vascular endothelial growth factor (VEGF) mRNA in cells and cultured skin substitutes (CSS) is increased by genetic modification. A. Diagram of replication-incompetent retroviral vector used for genetic modification of keratinocytes.16,17 B–D. Northern blots containing 10 μg of total RNA per lane were hybridized to a human VEGF probe. B. Control (−) and VEGF-modified (+) keratinocytes. C. CSS groups 1 to 4 (Table 1) in vitro at the time of grafting to mice. D. CSS in vivo, at 1 and 3 weeks after grafting. Solid arrows indicate locations of endogenous VEGF transcripts; open arrows indicate retroviral VEGF transcripts; LTR, long terminal repeat; CMV, cytomegalovirus promoter; Neo, neomycin resistance gene; ψ, retroviral packaging signal.