Gene expression values are generally converted to Z-scores for visualisation purposes, like, in heatmaps. The differential expression analysis itself is performed on normalised counts, prior to log and/or Z-score transformation. Any data can be converted to Z-scores, including FPKM values (edit: see zFPKM R package). The point again, however, is that the Z-score transformation is generally for visualisation in RNA-seq studies, or for other downstream analyses outside of the standard differential expression.

I don't see any major steps that need to be further applied after Z-score transformation for Figure 2B. Figure 2C, however, looks like the plotting of the first 3 dimensions after k-means clustering (hope that we're looking at the same figures).

Kevin

Can Z score be applied on log2FC and then visualized?

Alternatively, Can log2FC be converted to Z scores and then visualized as heatmap?