[Formation of germline chimeras from murine embryonic stem cell lines]

Generation of germline chimeras is the crucial step in ES cell-mediated transgenesis. The prerequisite for germline chimerism is the maintenance of germline differentiating potency of ES cells, whereas production of germline chimeras is the only method to prove whether such potency is maintained. In order to investigate the germline differentiating potency of three newly established ES cell lines (MESPU21, MESPU22 and MESPU29), ES cells were introduced into host embryos from inbred C57BL/6J and outbred KMW or ICR through blastocyst injection or 8-cell stage morula injection. Totally 81 chimeras were obtained; among 42 test-bred ones, 19 were germline transmitters assessed by coat analysis, as is the first report of ES cell-embryo germline chimeras in China. MESPU21 and MESPU22 formed germline chimeras in high frequency and most of those chimeras produced ES cell-derived progeny in high proportion, which proved that both ES cell lines retained good germline differentiating potency and could be used as valuable cellular vehicles to introduce genetic modifications into mouse genome.