Trisomy 8: a common finding in mouse embryonic stem (ES) cell lines

BACKGROUND: Obtaining a germ cell line is one of the most important steps in developing a transgenic or knockout mouse with a targeted mutated gene of interest. A common problem with this technology is that embryonic stem (ES) cells often lack, or are extremely inefficient at, germ line transmission. RESULTS: To determine whether chromosomal anomalies are correlated with inefficient ES cell germ line transmission, we examined 97 constructed ES cell lines using conventional cytogenetic analysis, and fluorescence in situ hybridization (FISH). Chromosomal abnormalities occurred in 44 (45%) out of the 97 specimens analyzed: 31 specimens had trisomy 8 or mosaic trisomy 8, eight specimens had partial trisomy 8 resulting from unbalanced translocations, and five specimens had other chromosomal anomalies. CONCLUSIONS: Our data suggest that chromosomal analysis is an important tool for improving the yield and quality of gene targeting experiments.