Karyotype of CHO DG44 cells

Abstract

The CHO cell line was mutagenized with radiation and by chemical treatment, and a CHO DG44 mutant carrying a double deletion for the dihydrofolate reductase gene located on chromosome 2 was isolated and characterized. Among the different sublines, CHO DG44 cells are widely used for the stable production recombinant proteins since they exhibit the DHFR-selection and amplification system. To our knowledge, the karyotype of CHO-DG44 cells has not been studied. After analysis of more than 100 metaphases, we consistently found 20 chromosomes whereas the normal diploid Chinese hamster genome was characterized with 22 chromosomes. The quasi-diploid CHO DG44 cells were found to have a karyotype altered from the original Chinese hamster. Only seven of the chromosomes were normal including the two chromosomes 1, one chromosome 2, 4, 5, 8 and 9. The four chromosomes Z1, Z4, Z8 and Z13 were identified as described by Deaven and Peterson (Deaven and Petersen 1973). The remaining chromosomes were 7 derivative chromosomes (rearrangement within a single chromosome or involving two or more chromosomes) and 2 marker chromosomes (structurally abnormal chromosome in which no part can be identified). We believe that insights from these studies can be of value for a genetic characterization of CHO DG44 cells expressing a recombinant protein as well as for work on targeted or homologous integration into the genome.