The viability of deep-frozen aggregated mouse embryos.

Since the first successful aggregation of mouse embryos was reported by TARKowsKi,ii) many studies on chimera production have been carried out.S'6'7) Chimeras produced by the aggregation of early embryos have been widely used in experimental investigations of mammalian embryolegy and developmental genetics.4'9) Chimeric experimental animals have also been used to study some problems of human genetic diseases. Recently, many mutant mice, some of which were affected by genetic diseases encountered in human beings, have been developed.3) However, these disease model mice have a relatively lower ability to survive and reproduce. Moreover, their maintenance requires great care and it is economically costly. Freezing of aggregated embryos from normal and disease model mice can be used to alleviate these problems. The purpose of this study is to investigate the viability of frozen-thawed aggregated mouse embryos, Embryos which were obtained by mating ddY female and ddY or C571BL male mice were used to investigate the in vitro and in vivo viability of aggregated embryos. Females were injected with 7.5 IU pregnant mare's serum gonadotropin followed by an injection of 7.5 IU human chorionic gonadotropin (HCG) 48 hours later. Feur-, 8and 12-N16-cell embryos were flushed from the oviduct by using Hanks' solution at 6e-76 hours post HCG injection. Recovered embryos were treated with Hanks' solution containing O.5% pronase at room temperature for 5 to 10 minutes to remove zona pellucida. Then embryos were washed several times and placed in modified Whitten's