Unique biological functions of different EPCs. The 737 and 665 early (A) and late (B) EPC genes were subjected to a Gene Ontology (GO) database search. These categories were selected from the “Biological Process” organizing principle in the GO database (http://www.geneontology.org/). The number of genes, gene symbols, and p values for each category that are significantly enriched are listed (p < 0.05). Underlined: discussed in the text. (C) Culture supernatant of early EPCs increases angiogenesis ability of late EPCs in 3D-angiogenesis assays. (D) Paracine factors uniquely expressed in early EPCs. (E) Validation of array data by real-time RT-PCR (n = 3). *: P < 0.05 by analysis of variance (ANOVA).