MYCN IS RETAINED IN SINGLE-COPY AT CHROMOSOME-2 BAND-P23-24 DURING AMPLIFICATION IN HUMAN NEUROBLASTOMA-CELLS

Amplification of the human N-myc protooncogene, MYCN, is frequently se en either in extrachromosomal double minutes or in homogeneously stain ing regions of ag gressively growing neuroblastomas. MYCN maps to chro mosome 2 band p23-24, but homogeneously staining regions have never be en observed at this band, suggesting transposition of MYCN during ampl ification. We have employed fluorescence in situ hybridization to dete rmine the status of MYCN at 2p23-24 in five human neuroblastoma cell l ines. All five lines carried, in addition to amplified MYCN in homogen eously staining regions or double minutes, single-copy MYCN at the nor mal position. In one line there was coamplification of MYCN together w ith DNA of the host chromosome 12, to which MYCN had been transposed. Our results suggest a model of amplification where MYCN is retained at its original location. They further sustain the view that either the initial events of MYCN amplification or the further evolution of ampli fied MYCN copies follow mechanisms different from those leading to amp lification of drug-resistance genes.