TABLE 1.

Extents of ectopic expression of MyoD in mEFs derived from p38α^−/− and wild-type p38α embryos^a

mEF type	Transfectant(s)	% MHC-positive cells in expt:
		1	2
wt + vector	GFP	<1	<1
wt	MyoD	17	22
−/− + vector	GFP	<1	<1
−/−	MyoD	9	12
−/−	MyoD + p38α	15	23

^amEFs were isolated from either p38 null (−/−) or wild-type (wt) embryos. Myogenic conversion was activated by transfection of MyoD with or without cotransfection of p38α kinase. After 3 days of culturing in (DMEM plus 2% horse serum), cells were fixed and the extent of myogenic conversion was evaluated by double staining for MyoD (using the monoclonal antibody 5.8) and a polyclonal anti-MHC antibody. Vector-transfected cells were visualized by transfection of the green fluorescent protein (GFP). The percentage of cells doubly positive for MHC and MyoD (or MHC and GFP) among 100 MyoD-positive cells was calculated.