Cytogenetic analysis of the bipotential murine pre-B cell lymphoma, P388, and its derivative macrophage-like tumor, P388D1, using SKY and CGH

Spectral karyotyping (SKY) and comparative genomic hybridization (CGH) were used to elucidate the divergent cytogenetic make-up of the prototypical bi lineage lymphoblastic pre-B lymphoma, P388, and its progenitor macrophage-l ike tumor, P388D1. P388 was found to be diploid and genomically stable. P38 8D1 was triploid, highly unstable and characterized by numerous marker chro mosomes (Chrs) and composite rearrangements. The karyotype of P388D1 was so complex that its clonal relatedness to P388 would have remained questionab le without confirmation by molecular analysis of the clonotypic immunoglobu lin heavy-chain and light-chain gene recombinations that coexisted in both tumors. The intrinsic instability of the P388D1 genome was indicated by the observation that only four out of 42 aberrations uncovered by SKY (in a to tal of 27 metaphases) occurred consistently (100% incidence), whereas 27 ch anges occurred non-randomly (27 to 96% incidence) and 11 alterations random ly (4 to 11% incidence). Persistent cytogenetic instability was also observ ed in P388 'macrophages' after phorbol ester- and ionomycin-induced convers ion in vitro of P388 lymphoma cells. The 'cytogenetic noise' in these cells was manifested by a multiplicity of sporadic chromosomal aberrations; ie 2 5 distinct changes were identified by SKY in 40 metaphases. The results in P388D1 and P388 'macrophages' were interpreted to indicate that the myeloid differention program in the bipotential pre-B cell lymphoma P388 is invari ably characterized by karyotypic instability. The study presented here demo nstrates the power of the combined SKY and CGH approach to resolve complica ted karyotypes of important and widely used mouse tumors.