Abstract:
The development of a somatic cell nuclear transfer procedure for theproduction of blastocyst stage cattle embryos is described. Bovine fetalfibroblasts were used for fusion experiments with surgically enucleatedoocytes (cytoplasts) following the establishment of optimal parameters forelectrofusion from isofusion contours. Fusion rates were increased bydecreasing size of the cytoplasts used but cleavage was decreased bydecreasing size of the cytoplast used (quarter, half and whole cytoplasts).The use of double cytoplasts did not improve cleavage, and development toblastocysts could not be achieved. In a comparison of electrofusion offibroblasts with cytoplasts in the subzonal perivitelline space withintracytoplasmic injection of nuclei and parthenogenetically activatedoocytes, 2%, 14% and 24% developed to blastocystsrespectively. In the group injected with isolated nuclei, the passage number(4 to 9) had no apparent influence on developmental competence to blastocysts.The embryos produced by nuclear injection of somatic cell nuclei showed thenormal pattern of cell surface appearance of TEC-3 and TEC-4 stage-specificepitopes during development, as seen in fertilized oocytes. We conclude thatthe nuclear injection of somatic cell nuclei is a relatively efficient way toclone bovine embryos.