Collapsed cluster diagram of porcine GI tract expression network together with the average gene profile of transcripts within selected clusters. A. Collapsed cluster diagram shown here is a simplified view of the graph used for the analysis of the GI tract [see Additional file 6, Figure S2 for screenshot of transcript level graph]. Each node represents a cluster of genes, the size of the node being proportional to the number of individual nodes (probesets) with that cluster. Edges represent connections between clusters whereby nodes in one cluster share edges with nodes in another. The color of the nodes has been selected to represent clusters of genes expressed in similar tissue types. B. Block diagrams of the average gene expression profile of the major GI clusters. Expression levels are indicated as a % of maximum with values rounded to the nearest 10%, each GI compartment analyzed being represented as a separate block. A key to the size of each block is shown in the bottom right hand corner. Gene clusters have been grouped according to cell type of origin: purple, stratified squamous epithelia; brown, salivary stratified columnar epithelia; light green, ciliated/glandular columnar epithelia; dark green, immune cells/cell cycle; blue, musculature (smooth and skeletal); grey, neuronal. GI, gastrointestinal.