Piwi-interacting RNAs (piRNAs) are a class of small non-coding RNAs. Their length ranges from ~22 to ~34 nucleotides depending on the organism and developmental stage. They have been identi ed in both vertebrate and invertebrate animals. To date, the main role of piRNAs is the silencing of transposable elements. In animals de cient in the piRNA pathway, transposons move freely leading to genome instability and sterility . Interestingly, piRNAs have been shown to mediate transgenerational epigenetic memory .
In mice, most piRNAs originate from long precursor transcripts known as piRNA clusters. These transcripts eventually get processed into mature piRNAs by a mechanism still poorly understood .
To better understand piRNA biogenesis and their mechanisms of action, we are exploring the genetic and epigenetic variations in piRNAs between 16 di erent strains of mice . Taking advantage of recently developed, reference-quality de-novo assemblies for those genomes, we are conducting a genome-wide comparative study and investigating the degrees of structural variation in piRNA-abundant regions. So far, small-RNA sequencing on four developmental stages (two embryonic and two post- partum) of these 16 strains has been performed. Results from our rst analyses will be presented. These will help in understanding the interplay between genomic variation and changes in piRNA populations between strains, developmental timepoints, and individuals. Future directions of this work will be discussed, as transgenerational e ects of piRNAs will be studied by performing crosses between some of the strains. This project is timely and therefore we anticipate that its completion will provide the community with a comprehensive resource.