Fig. 1.

Inefficient reprograming of old fibroblasts. a Schematics of the reprogrammable mouse line i4F in which the OSKM reprogramming factors (Oct4, Sox2, Klf4, and c-Myc) are expressed from a single genomic locus using a doxycycline-inducible transgene. Mouse embryonic fibroblasts (MEFs) and fibroblasts isolated from adult (10–30-week old) and old (70–100-week old) mice were induced with doxycycline for 2 weeks. b Quantification of AP⁺ clones. c Reprogramming efficiency relative to MEFs. d, e qRT-PCR analysis of Zeb2 (d) and Snail (e) mRNA in MEFs and fibroblasts from adult and old mice that were either not exposed to doxycycline or induced for 2 weeks. For all graphics depicted, Student’s t test (two-tailed) statistics, *p < 0.05, **p < 0.01, and ***p < 0.001; error bars represent standard deviation; n=experiments with independent cell cultures. f Immunofluorescence for Zeb2 in MEFs and old fibroblasts. The corresponding images stained with DAPI are shown (scale bars correspond to 10 μm). g Immunoblot for Zeb2 and β-actin in total cell lysates from two independent early-passage cultures of MEFs and old fibroblasts