Nuclear structural conditions and PCR amplification in human preimplantation diagnosis

An understanding of the relationship between nuclear morphology and DNA function is important in cytology and preimplantation diagnosis. In this study, direct polymerase chain reaction (PCR) amplification was used to diagnose the common delta F508 mutation of cystic fibrosis in 62 biopsied human embryo cells. The nuclei were photographed and classified into three categories depending on their microscopic appearance; these were further correlated with the results of PCR amplification. The normal nucleus group (42 embryo cells, with clear and regular nuclear membrane, transparent nucleoplasm and prominent nucleoli) showed 100% PCR amplification, with normal amplification results, i.e. bright DNA bands. These were considered to be the living cells. Only half of the cells (10 embryo cells) which contained abnormal nuclei (with abnormal nuclear membranes or nucleoplasm) showed PCR amplification, often with abnormal amplification results, i.e. weak DNA bands. These cells were considered to be either degenerate or to be undergoing degeneration. The anuclear cells (10 embryo cells) were composed of living (metaphase) and degenerated cells and showed about 30% PCR amplification. These results demonstrated that one of the important signs of early visible cell degeneration is the partial or total degeneration of the nucleus. Abnormal morphological changes of the nuclear membrane and nucleoplasm are usually accompanied with functional and structural DNA alteration. It is suggested that base degradation occurs earlier than the breakage of base-sugar bonds and phosphodlester bonds during the course of DNA degradation. The selection of optimal cells with a normal nucleus for single cell embryo biopsy is important for the precision and safety of preimplantation diagnosis.