HES1 and neoplasm: Moreover, the high Lef1 levels in the tumor cells appeared not to be a result of the deregulated Notch signaling, as inhibition of the Tcf1−/− tumor cells by DAPT only mildly affects Lef1 levels, whilst both Notch target genes Hes1 and Deltex were completely down-regulated (Figure 6A, right figure).