Comparison of heat-treated and tetraploid blastocysts for the production of completely ES-cell-derived mice

The present study compared the production efficiency and incidence of postnatal death in mice derived by injecting embryonic stem (ES) cells into either heat-treated blastocysts or tetraploid blastocysts. The proportion of completely ES-cell-derived mice from the tetraploid blastocyst group (3.3%) was significantly higher than that obtained from the heat-treated blastocyst group (1.5%). The incidence of postnatal death was the same between the two groups: 10 of 15 young (67%) in the heat-treated group and 21 of 34 young (62%) in the tetraploid group died within 13 days of birth. The remaining young grew to adulthood, had normal fertility, and their germ cells were of ES cell origin. There was no clear correlation, however, between the postnatal lethality of ES-cell-derived mice and the genetic background of the ES cells. The causes of postnatal death are discussed.