Myc overexpression in R26-βcat leukemic cells. (A) CGH-array profiles of the Myc locus on chromosome 15 for 10 R26-βcat tumors. The y-axis represents the log2 of the ratios of the normalized hybridization signals of leukemic/control DNA (black stars). The blue line represents the smoothed segmentation based on a Taut String method. The red line depicts status assignment (+1, 0, or −1 for gained, normal, or lost alleles, respectively; PISSCO algorithm). The position of the CGH probes is indicated on the x-axis. The locations of the Myc and Pvt1 genes are shown by green lines. (B) FISH analysis with paints specific for chromosome 14 (green) and 15 (red) on metaphase spreads from control lymphocytes and R26-βcat tumor cell lines. Representative metaphases show an amplification of chromosome 15 or chromosomes derived “Der” from the t(14;15) translocation in the cell lines from R26-βcat tumors as illustrated by the corresponding diagrams. (C) Quantitative reverse-transcription PCR analysis of Myc mRNA levels in thymocytes from control, 6-week-old R26-βcat mice and R26-βcat tumor cells. Values are shown relative to that of ubiquitin mRNA. Quantitative PCR reactions were performed in triplicate (mean ± SD). (D) Western blot analysis for Myc and N-Myc in total cell extracts from thymocytes of 2 control, 3 6-week-old R26-βcat mice and leukemic cells from 9 R26-βcat tumors.
