The system is completely transparent, allowing the user to trace back the actual Pubmed records the inferred associations are based upon. Genes in cluster 1 of the k-means clustering were progressively downregulated over time. Common concepts associated with the genes in this cluster included cell-cycle progression and DNA maintenance. In contrast, genes in clusters 4 and 6 showed progressively increased expression. As expected genes in these two clusters were mainly basal cardiogenic factors implicated in myocardial differentiation. Concept analysis identified genes involved in extracellular collagen BU 4061T composition and maintenance. Also alterations in proteoglycan composition, Tgfb and Ras signaling were indicated. A distinction between early, intermediate and late changes in expression could be discerned representing cardiac specification, maintenance and maturation, respectively. Cluster 3 shows a transient increase in expression up to 24�C48 hours in culture that coincides with the specification phase that precedes commitment to the cardiomyocyte lineage. This cluster contains Bmp2, a known factor involved in cardiac induction and specification. Genes with correlated expression profiles are speculated to have related biological properties. Therefore, Wif1 and Fgf12, also in this cluster, represent candidate genes for cardiomyocyte specification. Cluster 2 contains genes associated with the dystrophin-glycoprotein complex and myosin light chains and suppressor of cytokine signaling proteins. Several Wntsignaling related genes can be found in cluster 5 which display a sharp increase in expression at day 5, e.g., two members of the secreted Wnt MG132 antagonist family, Dkk3 and Frzb, and two members of the Frizzled related receptor family, Fzd2 and Fzd7. Given the large number of differentially-expressed genes identified in this paper an in depth description of all genes in the individual clusters is not possible. A list with all differentially expressed genes is available in the Table S1. Taken together, these data indicate that different phases during cardiomyocyte differentiation from chicken PE cells can be distinguished. Moreover, the differentially expressed genes in cluster 3 may represent previously unknown modulators for cardiac specification. In contrast to PE explants, explanted Epi cells cannot differentiate into a cardiomyocyte phenotype. In order to gain more insight into the processes underlying this Epi-to-myocardiallock, we compared the PE explant expression data with gene expression profiles derived from a series of different stages of epicardial development, i.e., prior to vessel formation, when intra-cardiac vessels have started to form, when the coronary circulation has matured but is not yet perfused and when coronary circulation is functional.