Figure 1.

Karyotypic evolution in the U2-OS osteosarcoma cell line. (A) Representative, pseudo-colored, multicolor-FISH karyotypes of ten major subclones (Sc), from five U2-OS-derivative cell lines (SL) composed of 69–80 chromosomes. In U2-OS cells, every homologue of the human karyotype is affected by clonal structural or numerical aberrations. Despite the karyotypic diversity, a monoclonal origin of all side lines is evident by the common presence of six identical recombinant chromosomes (pink arrows). Based on the constitution of chromosome 5, the WT1 cells probably represent the most ancestral population. The CDT1-overexpressing, and Doxorubicin-resistant R1 and R2 cells derive from WT2. White arrows depict clone-specific rearrangements. Note that several evolutionary steps (i.e., the process from WT1 to WT2 Sc1-2 or the evolution of CDT1 and R1 cells) were accompanied by karyotypes bearing multiple duplicated copies of identical clonal recombinant chromosomes (asterisks) suggesting that leaps in karyotypic evolution were accompanied by whole genome duplication (WGD) followed by multiple chromosome losses. (B) Jumping translocations of large recombinant segments clonally present in most U2-OS-derivative cell lines and subclones. (C) Chromoanagenesis was recorded only in one recombinant chromosome, composed of multiple alternate segments of chromosomes 5 and 19, in the chemo-resistant R2 cells. (D) Identical large genome imbalances identified by aCGH are stably maintained between the U2-OS-derivative cell lines despite the karyotypic alterations produced by extensive chromosome breakage and illegitimate rejoining. Red circles indicate the presence of the same imbalance in all 5 cell lines, pink circles depict undistinguishable duplications/deletions in 4 out of 5 karyotypically-diverse U2-OS cell lines. Lower boxes include partial karyograms involving genomic material of the chromosome analyzed by aCGH, representing two major subclones per side line.