| Abstract: | MYCN amplification has been observed in diverse neuronal tumors including neuroblastoma, retinoblastoma, and small cell carcinoma of the lung, and has been correlated with a poor prognosis in advanced-stage neuroblastomas. Recent studies have shown a co-amplification of DDX1, a DEAD box gene, and MYCN in retinoblastoma and neuroblastoma. DDX1 has been mapped to within a megabase of the MYCN gene in band 2p24. In the present study, the relational map of DDX1 and MYCN by fluorescence in situ hybridization (FISH) mapping to metaphase cells and extended free chromatin fibers indicated that DDX1 is telomeric to MYCN. Dual-color FISH analysis of amplicons within arrays of extended chromatin fibers was performed to examine the physical relationship of MYCN and DDX1 within double minute chromosomes (dmins) and homogeneously staining regions (hsrs). No regular reiterated amplicon repeat unit was present in the hsrs, but detailed analysis of the configurations of DDX1 and MYCN within each array indicated that multiple rearrangements generated a complex hsr amplicon structure. Similarly, analysis of a cell line bearing dmins showed that a composite amplicon structure involving deletions and/or duplications of MYCN and DDX1 is a feature of dmin formation. These data are consistent with a molecular mechanism involving many rearrangements during the evolution of gene amplification, resulting in complex amplicon structures with distinct changes in relative gene copy number and considerable variation in intragenic distances between coamplified genes. Genes Chromosomes Cancer 20:243–252, 1997. © 1997 Wiley-Liss, Inc. |
