Current State of the Art in Large Animal Cloning: Any Lesson?

Following fertilisation, major changes occur in the organisation of chromosomes and genes in the zygote that contributes to the formation of totipotent cells and their ensuing differentiation to the diverse cell lineages in the organism. The aim of animal cloning through Somatic Cell Nuclear Transfer (SCNT) is to reestablish the reprogramming that occurs in the fertilized embryo. SNCT often leads to abnormal development with a majority of concepti lost before birth. Imprinted genes are amongst the most frequently affected genes, and their altered expression could in part explain the observed developmental phenotypes. Here, we report our experience in sheep cloning. We describe the major phenotypic abnormalities observed in the extraembryonic tissues of sheep clones and suggest some possible strategies to improve SCNT.