Here is the code I used:
DotPlot(object = cluster, genes.plot = c("Hcn4","Shox2","Nkx2-5","Nppa","Tnnt2","Gja5","Tbx18","Tbx3","Isl1","Scn5a","Cacna1d"), plot.legend=TRUE)
I was confused about the legend with the Negative number shown for avg.exp.scale
. Does it mean that the cluster expressed the genes at low level or that gene was down regulated? (like the Shox2 in the "0" compared with "2").