Fig. 1.

Overview of transcriptome changes after treatment of melanocytes with ASP or αMSH. The microarray experimental design was based on competitive hybridizations of ASP- or αMSH-treated vs. untreated melanocytes after 3 h, 1 d, 2 d, 3 d, and 4 d of treatment. (A) Number of genes differentially altered in response to ASP or αMSH by at least 1.5-fold for at least 1 time point of the 5 assessed. (B) PCA analysis of 1,715 differentially expressed genes after treatment with ASP or αMSH (P < 0.01 and 1.5-fold at any 1 time point) for which data were present for all time points. Projection of the 3 principal components covering the highest variance (84% of the total variance) shows drug-dependent variation along PC#1 (70.7%), whereas time-dependent changes are observed along PC#2 (7.7%) and PC#3 (5.5%). (C) Hierarchical clustering of 1,638 genes altered either by ASP or by αMSH using an average linkage algorithm, underscores the overall inverse regulation of the genes by αMSH relative to ASP. Distance metric is 1 correlation. Horizontal stripes represent genes, and columns show experimental samples. Clustering was performed only on genes, whereas samples were ordered by drug and time. Logarithmic values of treated to untreated expression ratios are shown in the heat map using red and green color codes for up- and down-regulation, respectively. Black indicates no change, and gray represents missing data.