Detection of NPM-ALK and reciprocal ALK-NPM transcripts by nested RT-PCR. Total RNA was extracted from frozen skin biopsies or cultured cells and submitted to nested RT-PCR analysis, followed by electrophoresis on 2% agarose gel. Lanes 1, 2 and 3, cases no. 1, 2, and 3, respectively, CD30⁺ secondary CLCL; lane 4, case no. 4, LyP; lanes 5 through 11, cases no. 5 through 11, CD30⁺ primary CLCL; lane 12, t(2;5)⁺SU-DHL-1 cell line; lane 0, no template; lane M, molecular weight marker 100-bp DNA ladder (GIBCO-BRL). Detection of NPM-ALK transcripts: (A) ethidium bromide staining and (B) radioautography. Detection of ALK-NPM transcripts: (C) ethidium bromide staining and (D) radioautography. The gels were transferred to a nylon membrane, hybridized either with the NPM-ALK-J probe (B) or the ALK-NPM-J probe (D), and radioautographed. Sizes are indicated in bases.