Production of functional oocytes requires maternally expressed PIWI genes and piRNAs in golden hamsters

Many animals have a conserved adaptive genome defense system known as the Piwi-interacting RNA (piRNA) pathway which is essential for germ cell development and function. Disruption of individual mouse Piwi genes results in male but not female sterility, leading to the assumption that PIWI genes do not play a role in mammalian oocytes. Contrary to this, PIWIL1- and PIWIL3-defective golden hamsters we have produced show defects in production of functional oocytes. Mechanisms involved, however, vary between the two PIWI genes; lack of PIWIL1 has a strong impact on gene expression including hamster-specific young transposon de-silencing, while PIWIL3 deficiency has little impact on gene expression in oocytes, although DNA methylation of chromosomes was reduced to some extent. Our findings serve as the foundation for developing useful models to study the piRNA pathway in mammalian oocytes including humans, which cannot be possible with mice. small RNA sequencing, RNA sequencing, and whole genome bisulfite sequencing of PiwiL1 and/or PiwiL3 mutant hamsters.