Fig. 4

Evolutionary conservation of oocyte piRNA clusters. A Expression of piRNAs (quantified in RPM) in the 56 syntenic piRNA clusters in oocytes. Data are shown for piRNAs expressed in at least one species. The percentage of expressed piRNAs from the 56 piRNA clusters compared to overall oocyte piRNA expression is shown at left. Gray indicates the absence of a syntenic cluster in the indicated species. B Genome browser snapshots of a syntenic piRNA cluster found in several species, piC-ZNF518B-WDR1, from the 56 syntenic piRNA clusters shown in A. The black peaks indicate piRNA abundance in RPM. TE distributions in the corresponding genomic region are shown at the bottom. C The phyloP scores of the piC-ZNF518B-WDR1 of piRNA cluster, its 10 kb upstream and downstream flanking intergenic regions and cDNA sequences of adjacent protein-coding genes. The values represent -log p-values under a null hypothesis of neutral evolution. The sites predicted to be conserved are assigned positive scores while sites predicted to undergo accelerated evolution are assigned negative scores. D UpSet plot showing the identity of piRNA sequences in the piC-ZNF518B-WDR1 cluster among the 12 vertebrate species. The intersections of piRNA species are indicated by lines linking samples in the lower panel. piRNAs were classified as the same in multiple species if the piRNA length was < 23 nt and had ≤ 1 mismatch, or if the length was > 23 nt and had ≤ 2 mismatches. No mismatches were allowed in the seed region (2–8 nt). GP, guinea pig; GH, golden hamster; CH, Chinese hamster; ZF, zebrafish