Table 1.

Mouse cell strain	% O2	Culture condition	Growth status	Labeling Index	% SA-βGal	Designation
MEF (primary mouse embryonic fibroblasts)	3	presenescent, subconfluent	Growing	84	11	proliferating
	3	presenescent, cultured to confuency	Quiescent	16	nt	PRE
	3	X-ray-induced growth arrest	Senescent	4	74	SEN (XRA)
	20	presenescent, subconfluent	Growing	75	12	proliferating
	20	presenescent, cultured to confuency	Quiescent	15	nt	PRE
	20	growth arrest after repeated passage	Senescent	39	65	SEN (OXI)
mBF (primary adult mouse mammary gland fibroblasts)	3	presenescent, subconfluent	Growing	91	9	proliferating
	3	presenescent, cultured to confuency	Quiescent	15	nt	PRE
	3	X-ray-induced growth arrest	Senescent	4	76	SEN (XRA)
	20	presenescent, subconfluent	Growing	86	9	proliferating
	20	presenescent, cultured to confuency	Quiescent	13	nt	PRE
	20	growth arrest after repeated passage	Senescent	42	65	SEN (OXI)