Sus scrofa Transcriptome or Gene expression

So far, the majority of research on piRNAs was carried out in popular model organisms such as fruit fly and mouse, which however do not closely reflect human PIWI biology. Thus, we high-throughput sequenced and computationally analyzed piRNAs expressed in the adult testis of the pig owing to its full set of mammalian Piwi paralogs, availability for repeat experiments and the existence of elementary data from previous studies on the porcine PIWI/piRNA system. We provide an exhaustive characterization of porcine piRNAs and genomic piRNA clusters. In addition, we reveal that a considerable proportion of piRNAs matches protein coding genes, exhibiting characteristics that point to a biogenesis within the post-transcriptional silencing mechanism of the PIWI/piRNA pathway, commonly referred to as ping pong cycle. We further show that the majority of identified piRNA clusters spans exonic sequences of protein-coding genes or pseudogenes, which indicates the existence of different mechanisms for the generation of piRNAs directed against mRNA. Our data provides evidence that spliced mRNAs, derived from such loci, are not only targeted by piRNAs but are also subject to ping pong cycle processing. Finally, we demonstrate that homologous genes are targeted by piRNAs in pig, mouse and human. Altogether, this strongly suggests a role for mammalian piRNA clusters in gene regulation alongside of TE repression.