Figure 4.

Grouping single cortical neurons by their global expression profiles. Ten neurons from layer II/III of somato-sensory cortex of young mice (P13–P22) were recorded from and expression profiled as described (Figure 1 and Materials and Methods). Cells were clustered based on Pearson correlation coefficients as a measure of similarity in gene expression. Clustering of these cells without averaging gene expression between the dye-swapped technical array replicates (A) resulted in the formation of two distinct clusters containing primarily fast-spiking neurons (yellow circles) or regular spiking neurons (blue circles), in each case with one RS and one FS neuron misassigned to each cell type cluster. Numbers within circles correspond to the cell identifiers used in Figure 3. Averaging gene expression between replicate arrays (B) did not change the cluster composition. In each cluster, each column represents expression data from a single array (A) or cell (B), each row expression ratio for a single gene. By convention, red colours indicate positive expression (enrichment) and green lower expression. The range of expression values is indicated by the colour bar beneath each cluster.