Amplification of a DEAD box gene (DDX1) with the MYCN gene in neuroblastomas as a result of cosegregation of sequences flanking the MYCN locus

A DEAD box gene (DDX1) characterized by a motif with a putative RNA helicase was found at elevated levels, with multiple copies, in a neuroblastoma and in some retinoblastoma cell lines in which the MYCN gene was amplified. The present study was aimed at determining whether amplification of the DDX1 gene is critical for human neuroblastomas exhibiting MYCN gene amplification. Extended DNA panels of tumors and cell lines revealed amplification of the DDX1 gene in approximately half of the specimens exhibiting MYCN gene amplification, which is in good agreement with a finding reported recently. Because its profile was similar to that of the cDNA marker G21 and another flanking DNA marker, clone 8, both of which localize outside the core of the amplicon of the MYCN gene, we noted that we could localize the DDX1 gene in relation to the MYCN gene. Utilizing pulsed‐field gel electrophoresis according to a method based on the combinatorial alignment of multiple single digests and a 5.5‐megabase map surrounding the MYCN locus, we mapped the DDX1 gene within a 100 kb region about 400 kb upstream from the MYCN gene, where G21 is localized. Further hybridization experiments with both genes, complete sequencing of G21, and its comparison with that of the DDX1 gene eventually confirmed that the DDX1 gene is identical to G21. G21 is a cDNA clone isolated by differential screening of a library from a neuroblastoma cell line, IMR‐32, but its function has not yet been identified. Coamplification of the DDX1 gene with the MYCN gene is a consequence of the segregation of continuous DNA stretches spanning both loci during the amplification process. Genes Chromosom Cancer 15:129–133 (1996). © 1996 Wiley‐Liss, Inc.