Stage‐specific appearance of the mouse antigen TEC‐3 in normal and nuclear transfer bovine embryos: Re‐expression after nuclear transfer

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Abstract
Bovine embryos, recovered from the uterus in vivo or derived from in vitro matured and in vitro fertilized oocytes, were investigated for the presence of the developmentally regulated mouse antigen TEC‐3 by indirect immunofluorescence. During preimplantation embryo development TEC‐3 is expressed on bovine morulae and blastocysts. It is absent from unfertilized and fertilized oocytes, and from all stages before the 32‐cell stage. The finding that TEC‐3 is not expressed before the onset of embryonic transcription, which occurs at the eight‐cell stage in the bovine, but only when the embryonic genome is active, makes it a potential marker for studying nuclear reprogramming after nuclear transfer. Nuclear transfer embryos were made by electrical fusion of blastomeres from morulae derived in vivo with enucleated metaphase II oocytes. Indirect immunofluorescence with the TEC‐03 antibody showed that the TEC‐3 antigen, present on blastomeres of the morula stage embryo, disappeared after fusion and was expressed again when the nuclear transfer embryos developed to the morula and blastocyst stage. These data suggest that the bovine embryonic nucleus may be able to revert to the equivalent of an earlier developmental stage when transferred to ooplasm, and is then capable of following the normal developmental program.