The myc oncogenes are frequently activated in human tumors, but there is no comprehensive insight into the target genes and downstream cellular pathways of these transcription factors. We applied serial analysis of gene expression (SAGE) to identify targets of N‐myc in neuroblastomas. Analysis of 42 000 mRNA transcript tags in SAGE libraries of N‐myc‐ transfected and control neuroblastoma cells revealed 114 up‐regulated genes. The majority of these genes have a role in ribosome assembly and activity. Northern blot analysis confirmed up‐regulation of all tested transcripts. Induction was complete within 4 h after N‐myc expression. The large majority of the ribosomal proteins were induced, as well as genes controlling rRNA maturation. Cellular rRNA content was 45% induced. SAGE libraries and northern blot analysis confirmed up‐regulation of many of these genes in N‐myc‐amplified neuroblastomas. As N‐myc can functionally replace c‐myc, we analyzed whether N‐myc targets were induced by c‐myc as well. Approximately 40% of these N‐myc targets were up‐regulated in a c‐myc‐transfected melanoma cell line. These data suggest that myc genes function as major regulators of the protein synthesis machinery.

Saethre-Chotzen syndrome, a common autosomal dominant craniosynostosis in humans, is characterized by brachydactyly, soft tissue syndactyly and facial dysmorphism including ptosis, facial asymmetry, and prominent ear crura. Previously, we identified a yeast artificial chromosome that encompassed the breakpoint of an apparently balanced t(6;7) (q16.2;p15.3) translocation associated with a mild form of Saethre-Chotzen syndrome. We now describe, at the DNA sequence level, the region on chromosome 7 affected by this translocation event. The rearrangement occurred approximately 5 kb 3' of the human TWIST locus and deleted 518 bp of chromosome 7. The TWIST gene codes for a transcription factor containing a basic helix-loop-helix (b-HLH) motif and has recently been described as a candidate gene for Saethre-Chotzen syndrome, based on the detection of mutations within the coding region. Potential exon sequences flanking the chromosome 7 translocation breakpoint did not hit known genes in database searches. The chromosome rearrangement downstream of TWIST is compatible with the notion that this is a Saethre-Chotzen syndrome gene and implies loss of function of one allele by a positional effect as a possible mechanism of mutation to evoke the syndrome.

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