Production of Experimental Chimeras in Livestock by Blastocyst Injection
Mammalian embryos have the interesting property that allows them to be combined to form a normal individual containing cells of 2 distinct geno-types. Although this mixing of embryonic cells or chimerism occurs naturally (see Ref. 3 for review), whole body chimerism is relatively rare. Nicholas and Hall (13) attempted to produce chimeras in the laboratory by aggregating one-cell rat embryos, however, no conclusive evidence could be offered in terms of chimerism. Tarkowski (16) was the first to develop a procedure by which chimeras could be readily produced. Immediately following, Mintz (10,11) published a similar method but with modifications that resulted in a simpler procedure. Briefly, the zonae pellucidae were removed either mechanically or enzymatically from early cleavage-stage embryos, the 8-cell stage being the most common. Two embryos of different strains were then placed in contact with each other and allowed to aggregate into a single embryo. The chimeric embryos were allowed to develop to the blastocyst stage and then transferred to suitable recipients. The ability to readily produce large numbers of whole body chimeras proved to be a valuable tool in the study of embryology and developmental genetics (see Ref. 9 for review).
KeywordsZona Pellucida Inner Cell Mass Control Knob Spleen Cell Suspension Chimeric Embryo
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