Figure 2. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation of host genes. (A) Schematic diagram of the DE-circRNAs between young and aging groups. (B) The volcano plot is constructed using fold-change and P-values. The vertical lines correspond to 2.0-fold up- and down-regulation between YA and AA samples, and the horizontal line represents a P-value. Green and red circles represent differentially expressed (DE) circRNAs with statistical significance (fold change > 2.0 and P < 0.05). Green circles represent the down-regulated circRNAs, whereas red circles represent the up-regulated circRNAs. (C) Hierarchical clustering analysis of DE-circRNAs in the ovarian tissues of three young (< 30 years) and three older (> 40 years) women. The expression values (Fold change > 2.0, P < 0.05) were represented in different colours, indicating expression levels above and below the median expression level across all samples. (D) Top 20 GO terms in each category, and top 20 KEGG signalling pathway annotations (E and F).