Fig. 6. RA acts synergistically with ß-catenin to induce neuronal differentiation in ES cells. (A) The percentage of ß-tubulin 3-immunoreactive cells was quantified from high density inductions with or without RA treatment (see Materials and methods). ß-catenin N induced a greater proportion of neurons than ß-catenin C did. Treatment with RA, along with either ß-catenin C or N, resulted in an increase in the number of neurons, suggesting that there is synergy between RA and ß-catenin signaling (ND, none detected; error bars show s.d.). (B) Cells with neuronal morphology from these cultures were patch clamped to determine whether they expressed voltage-gated ion channels (see Materials and methods). All cultures showed voltage-gated ion channel activity. A representative tracing from neurons induced from ß-catenin C transfected ES cells at high density without RA is shown. Cells from control conditions did not exhibit this activity (data not shown). Cells were held at -90 mV holding potential and activated at -30 mV.