[Production of chimeras by embryo microsurgery and their possible application in cattle breeding]

An important contribution to genetic and embryonic engineering in mammalian embryos is the production of chimeric mammals. Chimeras can be produced by aggregating the blastomeres of two different embryos to make a single individual. A method is described to produce bovine chimeras by aggregating non-surgically collected embryos of different breeds and transferring the aggregated embryos nonsurgically to synchronised recipients. An overt chimeric bull calf (Holstein-Friesian and Brown-Swiss) was born on March 31st, 1984. Chimeras have many uses in research, but one practical use is to rescue defective embryos that would not develop to term on their own. Such embryos can be aggregated with normal blastomeres to produce a chimera. Some of the initially defective cells can even become part of the germ line in the chimera and give rise to perfectly normal eggs or sperm. Two models for using this technique in cattle research are described. The lethal disorder arachnomelie has a rather high frequency in some German Brown-Swiss populations. Chimeric calves developing from embryos descending of carrier matings could help to find out the genetic and developmental background of this disorder. Chimeras produced of transgenic teratocarcinoma cell lines and normal embryos offer one possibility to produce transgenic cattle. The advantages and disadvantages of these possibilities are discussed.