Please note that the B6/Blu ES cells are available only to WUMS investigators until licensing agreements have been completed.

Due to an expressed interest by many investigators, the ES core now offers a new ES cell line to the Washington University research community. The line is derived from a C57BL/6 transgenic line that contains a LacZ reporter that allows easy chimeric determination. The transgene is a Beta-globin LacZ fusion, and it is expressed exclusively in peripheral red blood cells (for details of the cassette and expression patterns, see Graubert et al., Nucleic Acids Research 26:2849-2859, 1998; the ES line was made from transgenic line 'A"). These transgenically marked B6 ES cells can be injected into B6 blastocysts to create chimeric mice in the usual fashion. However, instead of determining chimerism visually by coat color or assessing chimerism genotypically in tail DNA, chimerism is assessed quantitatively in the mesoderm by assessing LacZ expression in a single drop of tail blood obtained at weaning. Protocols and controls for the quantitative analysis of LacZ levels will soon be available from the ES core.

The C57Bl/6 strain used to create this ES cell line was obtained from Taconic. To our knowledge, there have not been any satellite marker studies that compare B6 lines between different vendor sources. Until this study has been done, we recommend that the donor mouse strain for blastocysts come from Taconic to maintain strain consistency. In addition, the strain and commercial source for the public consortium mouse genome sequencing project is C57BL/6 from The Jackson Laboratory. Taconic obtained the C57BL/6 line from Jackson Labs in 1991 at generation F151.

The new ES cell line, B6/Blu-1, has been karyotyped and also analysed by spectral karyotyping; the cells have a normal complement of chromosomes and are XY. The cells have been MAP and mycoplasma tested and are pathogen free. The transgene has been mapped to mouse chromosome 4 and is present on only one chromosome. It can easily be bred out of the mice after the desired mutation is transmitted through the germline. B6/Blu-1 ES cells have shown to support homologous recombination events, and they have subsequently gone germline. We have also removed a LoxP flanked neo cassette from a targeted ES line by transiently overexpressing Cre recombinase in the cell. These doubly manipulated clones have yielded highly chimeric mice which are currently being bred for germline transmission.