Quantitative estimation of chimerism in mice using microsatellite markers

An embryonic stem cell line was established from SV129 mouse blastocysts and used to generate chimeric mice by injection into OF1 blastocysts; 18 out of the 30 resulting offspring appeared chimeric as judged from their coat color patterns, and 3 of the 13 males proved to be germ-line chimeras as they transmitted the SV129 agouti phenotype to all or part of their offspring. The degree of chimerism of these males was evaluated for different tissues using polymorphic microsatellite markers amplified by the polymerase chain reaction. It was shown that these new markers can be effectively used to quantitatively estimate levels of chimerism. The CKMM (creatine kinase, muscle) microsatellite system was used to distinguish the SV129 from the OF1 genotype. In all performed tests, the correlation between DNA ratio and signal ratio, expressed as a base 10 logarithm, was shown to exceed or equal 0.98 for known DNA ratios (SV129/OF1) ranging from 1/99 to 99/1. Linear calibration methods were used to predict the % SV129 DNA of a test sample based on the obtained signal ratio. The accuracy of the prediction was evaluated by performing repeated measurements. Differences among three repeated estimates ranged from 2 to 17% for a given sample. Microsatellite systems should be very useful to monitor chimerism involving strains that can not be discerned with coat color or biochemical markers. This will be particularly important when ES methodology becomes available in species other than mice.