[Progress on mechanism of nuclear reprogramming after nuclear transfer].

Despite cloned animals becoming almost commonplace, there is no perfect cloning technique system yet and behind every success lies hundreds of failures. Moreover, cloned animals often age and die quickly. All of those problems hinder further research in nuclear transplantation. The key to make a break-through in the research of cloned animals relies on elucidating mechanism of nuclear reprogramming. Therefore, progress on nuclear reprogramming in nuclear transplantation has been reviewed in some aspects, for example remodeling of the nuclear structure, nucleocytoplasmic interactions and effects of the cell cycle, difference of gene expression and genomic imprinting between reconstructed embryos and fertilized embryos, etc. These results indicate that cytoplasmic environment is very important for the reprogramming of transplanted nuclei. When a donor nucleus in any stage of the cell cycle is transferred into the cytoplasm of an oocyte, there are the twin processes of structural remodeling and molecular reprogramming of the nucleus after transplantation. It is evident that the cell cycle coordination between donor cell and recipient cytoplast to avoid DNA damage and to maintain correct ploidy of the reconstructed embryo is of critical importance in determining the developmental capacity of reconstructed embryos. A dramatic reprogramming of gene expression occurs during zygotic gene activation. The time of zygotic gene activation may affect nuclear reprogramming and consequently the development of reconstructed embryo to off-spring. Imprinted genes are related to the reprogramming and aberrant development seen in manipulated embryos, and may be critical in the reprogramming of transplanted somatic cell.