Fig. 1. Reduced NF-B activity in skin of c^IBN and downless mice, but normal perinatal epidermal keratinocyte differentiation in c^IBN mice. (A) Total protein extracts of newborn wild-type and c^IBN (N) skin were analysed for IBN expression in a western blot using an anti-IB antibody (lower panel). Mouse embryonic fibroblasts isolated from c^IBN mice were used as a positive control (N MEF, right lane). ß-Catenin protein levels remained unchanged in all extracts (upper panel). ns, non-specific. (B) EMSA of total skin extracts of newborn wild-type, c^IBN (N) and downless (dl) skin. Extracts were treated with specific antibodies against NF-B p65, p50 and RelB as indicated, which inhibited (-p65) or upshifted (-p50) the DNA-binding complex. No effect was seen with RelB. Strong p50 homodimer binding is present in skin extracts. (C) Sagittal cryosections of E17.5 and P0 wild-type and c^IBN (N) embryos were incubated with antibodies to different epidermal differentiation markers (AP substrate, in red), as indicated above (loricrin, involucrin, filaggrin, keratin 10). Counterstaining was carried out with Mayer's haemalaun (blue).