LysM and ERK1/2 mice express the expected mutations in germline DNA, but macrophages from ERK1/2 mice selectively retain expression of ERK2 protein.

<p>(A) DNA from clipped tails of LysM and ERK1/2 mice (three of each) was amplified to detect the mutant or wild-type alleles for <i>Lyz2</i>, <i>Erk1</i>, and <i>Erk2</i>. (B) Macrophages were derived from bone marrow cultures stimulated for 7 d with LADMAC-conditioned medium containing M-CSF, and expression of ERK1 and ERK2 was detected by Western blotting. Diagonal arrows indicate the position of the ERK2 band, expressed in ERK1/2 macrophages but greatly reduced in <i>Erk2</i>^{<i>flox/flox</i>}<i>Lyz2</i>^{<i>Cre/Cre</i>} macrophages. Results are representative of three independent experiments. Labels: B6, C57BL/6J; E1 E2^f/f, <i>Erk1</i>^<i>-/-</i><i>Erk2</i>^{<i>flox/flox</i>}; E1, <i>Erk1</i>^<i>-/-</i>; E2, <i>Erk2</i>^{<i>flox/flox</i>}<i>Lyz2</i>^{<i>Cre/Cre</i>}.