Cytogenetic analysis of biopsied preimplantation mouse embryos: implications for prenatal diagnosis

Genetic diagnosis of enzyme deficiencies have been developed in mouse models using biopsied preimplantation embryos. A technique for preimplantation cytogenetic analysis was developed using embryos which were biopsied at the 4-cell, 8-cell and morula stage. Three culture methods were compared, using exposure directly to colchicine or preculture or overnight culture with subsequent exposure to colchicine. Some biopsies were lost through cell death (4.7-20.3%) and technical problems (11.1-27.8%), whilst others remained in interphase (13.0-46.5%). Air-dried preparations were successfully G-banded and karyotyped by modifying routine banding procedures. Biopsies placed directly into colchicine yielded the greatest mitotic index. However, chromosome morphology was unsuitable for G-banded analysis. After a short preculture, 71.4% of fixed 8-cell biopsies were karyotyped. The success of analysis of 8-cell biopsies is probably partly related to the higher mitotic index of intact embryos at this stage. Loss of chromosomes through scatter and chromosome overlapping limited analysis, particularly in biopsies with only one metaphase. The present success rate is not acceptable for the application of this technique to human prenatal diagnosis. However, it presents a useful tool for the study of chromosomal error at the research level.