Fig. 5.

Induced myogenic differentiation of PS1^–/– MEFs is independent of γ-secretase activity. PS1^–/– mice die during embryogenesis and so, to examine myogenesis, we used MyoD-transfected MEFs. (A) Immunostaining revealed that PS1 is expressed by WT MEFs, but is absent from PS1^–/– MEFs. (B,C) Immunoblot analysis demonstrated that myogenesis was effectively induced in PS1^–/– MEFs by transfection of a MyoD-expression vector. β-actin was the protein loading control. (C,D) Culture in high-serum (10% FBS) medium for 5 days still resulted in MyHC expression (C) and formation of myotubes (D) in PS1^–/– MEFs, but not in WT. (E,F) WT MEFs transfected with the MyoD-expression-vector and exposed to 1 μM DAPT or 1 μM L-685,458 to inhibit γ-secretase activity failed to induce MyHC expression when cultured in 10% FBS for 5 days. However, MyoD-transfected PS1^–/– MEFs, maintained under identical culture conditions, differentiated and expressed MyHC, with inhibition of γ-secretase activity having no effect on the differentiation index. Data from at least three independent experiments are shown ± s.d. Scale bars: 20 μm (A), 100 μm (D) and 60 μm (E).