RT-PCR of tumor cells with primers designed to detect specific isoforms using the 5′ primer to straddle the splice junction site.

(A) An alternatively spliced species of Ang-1 mRNA in cells, determined by RT-PCR with a set of primers used to detect Ang-1 isoform 1.3 kb and designed to detect a 312-bp product. Lane 1, negative control without cDNA template; lane 2, DU145; lane 3, FS4; lane 4, MDA-MB468; lane 5, MDA-MB231; lane 6, MCF7; lane 7, CHRF. (B) Primers designed to detect the 0.9- and 0.7-kb isoforms, which give rise to corresponding bands 595 bp and 428 bp, respectively, in CHRF cells.