PPI network of liver filtered by different tissue expression profiles. The expression levels of the nodes are represented by differential levels of grey. Query nodes are marked with squares. PPIs are filtered with prespecified gene expression level (16384). The PPI networks filtered by liver and fetal liver expression profiles are similar, but some subtle differences can be noted. For example, interactions between HBA1 and HBG2 are present in the fetal liver but not in the (adult) liver. This reflects the actual compositional differences between fetal and adult hemoglobins.