Figure 1.

Derivation of skeletal myotubes and optogenetic motoneurons from a single donor. (A-B) Membrane expression of the channelrhodopsin 2- yellow fluorescent protein (ChR2-YFP) complex in (A) human induced pluripotent stem cells (hiPSCs) and (B) hiPSC-derived motoneurons. (C) Expression of the motoneuronal marker HB9 (red = HB9: green = ChR2-YFP; blue = DAPI). (D) Representative membrane potential traces from a ChR2-YFP-expressing hiPSC-derived motoneuron in which action potentials are evoked by light or current injection. The column of black traces (right) shows light-evoked action potentials elicited by a 1 s exposure to light of increasing intensities. The relative intensity of light is shown on the right of the trace, and it correspond to light power values of 4519, 1281, 475, 219, 81 and 0 μW/mm². The blue bar at the base of the column represents the period of light exposure. The column of traces in red (left) are recordings from the same cell with action potentials evoked by a 1 s current injection. The amplitude of current injection is shown on the right of the trace and was chosen to match the action potential firing pattern evoked by light. The current injection step period is shown at the base of the column. (E) Immunostainings showing the formation of multinucleated myotubes expressing the skeletal muscle markers α-actinin, desmin, myoD and myogenin after 2 weeks of differentiation (green = muscle marker, blue = DAPI). Scale bars: 100 μm.