Megabase-scale analysis of the origin of N-myc amplicons in human neuroblastomas

Abstract

In order to elucidate the initiation of the N-myc gene amplification, we have analyzed the original structures of the N-myc amplicons among 38 human neuroblastomas. Nineteen DNAs isolated from the N-myc amplicons recognized a continuous stretch totally encompassing a 5.5 megabase region spanning the normal N-myc gene. The co-amplification profiles with these DNAs showed that two of them, which mapped into a 300 kb region flanking the N-myc gene, were commonly amplified in most specimens, while others were differentially amplified among various subsets. These profiles enabled us to divide the N-myc amplicons into several groups and outline their original domains as a continuous stretches, pointing to the existence of 'consensus sites' for the ends of the initial domains in the original region. In one cell line, the domain was found to be several times larger than that of the derivative amplicon; and the rearranged sites identified within the amplicons, which showed no site specificity, were consistent with those deduced from the domain structure. These results lead to a model in which N-myc gene amplification is initiated at some consensus sites by a preferential mechanism and followed by a random loss of the domain structures during subsequent stages.

Co-amplification of a novel gene, NAG, with the N-myc gene in neuroblastoma

“…In addition, NAG and DDX1 show approximately the same frequency of co-ampli®cation with N-myc; thus, it is likely that both are located telomeric to N-myc. Akiyama et al (1994) have shown that within a 500 kb region¯anking N-myc two NotI restriction sites are located less then 50 kb from each other. DDX1 has been mapped within this region, which is frequently co-ampli®ed with N-myc (Akiyama et al, 1994).…”

“…Akiyama et al (1994) have shown that within a 500 kb region¯anking N-myc two NotI restriction sites are located less then 50 kb from each other. DDX1 has been mapped within this region, which is frequently co-ampli®ed with N-myc (Akiyama et al, 1994). It is possible that the CpG island associated with NAG contains one of these two NotI sites.…”

“…The N-myc gene spans approximately 7 kb, whereas the size of the N-myc amplicon varies between 350 kb to over 1 Mb (Akiyama et al, 1994;Hiemstra et al, 1994;Kanda et al, 1983). Co-ampli®cation of other¯anking genes, that may in¯uence disease progression, has been suggested (George et al, 1996;Squire et al, 1995).…”

Genes Proximal and Distal to MYCN Are Highly Expressed in Human Neuroblastoma as Visualized by Comparative Expressed Sequence Hybridization

“…The size of the MYCN amplicon can extend anywhere from 350 kb to 8 Mb in length, [3][4][5] demonstrating the great variability of amplicon sizes and the number of coamplified genes in NB. A frequently coamplified gene is DDXI (mapping position 2p24), belonging to a family of genes that encode DEAD (Asp-Glu-Ala-Asp) box proteins, implicated in a number of cellular processes, eg, in posttranscriptional and translational gene regulation.…”

Expression of two dead box gene (DDX1 amd DDX6) is independent of that of MYCN in human neuroblastoma cell lines

“…Several hundred-kilobases of flanking sequences are also amplified along with MYCN [4][5][6][7]. Within these amplification units, DDX1 was identified [8][9][10][11][12][13].…”