Basic study in cryopreservation and chromosomal analysis of single blastomeres.

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Biopsy of the preimplantation embryo has wide application as a tool to investigate the developmental potential of the preimplantation embryo and also offered a possibility for prenatal diagnosis. The purpose of this study were first, to examine the developmental potential of single blastomeres of four-and eight-cell mouse embryos, and second to investigate the possibility of successful cryopreservation and karyotyping of single blastomeres.(1) Removal of a single blastomere from 4- and 8-cell mouse embryos by extrusion technique did not affect development to the blastocyst stage in vitro (80% of control,75% and 78.3% of biopsied embryo at 4- and 8-cell stage, respectively). However,after transfer to pseudopregnant recipient mice, the implantation rates of biopsied embryos were significantly lower than intact-controls (24.3% at 4-cell, 34.8% at 8-cell and 50% at control, respectively).(2) Most single blastomeres had undergone several cell divisions in vitro. After a short culture of single blastomeres with subsequent exposure to colcemid for 16 hours, 27.3% of 4-cell and 52.2% of 8-cell biopsies were karyotyped. However, 20 to 30% of biopsied blstomeres were lost through cell death and technical problems.(3) Biopsied single blastomeres could not be successfully cryopreserved when the freezing medium contained 1.5M DMSO+0.25M sucrose and 5-step dilution method was used. The techniques developed in this study may provide the useful tool for the study of prenatal diagnosis.