Fig. 3

Bull sperm piRNA content. a Reads annotated as piRNAs showed a typical size distribution, with a majority of reads being 27–32 nt in length. b Among these reads, 54% matched perfectly to published piRNA sequences. The remaining reads were considered to be piRNA-like sequences, bearing mostly 3p and 5p changes (19% and 10% of reads, respectively) or a combination (17%) of 5p, 3p and/or substitutions. c Both piRNAs and piRNA-like sequences showed a specific nucleotide composition, with more than 84% and 66%, respectively, showing a preference for uracil at their 5p terminus. d The majority of piRNA are expressed at low levels (87% below 500 mapped reads), with only a few (1%) expressed above 100,000 mapped reads. e All piRNA biogenesis classes were identified in sperm, but sperm piRNAs were found to primarily derive from intergenic regions. f Gene-derived piRNAs showed a specific expression profile, with higher expression levels than the other classes