The non-redundant functions of PIWI family proteins in gametogenesis in golden hamsters

The piRNA pathway is essential for female fertility in golden hamsters and likely humans, but not in mice. However, the role of individual PIWIs in reproduction remains poorly understood outside of mice. Here, using golden hamsters, we establish dynamic expression profiles and subcellular localization for all four PIWIs and characterize their associated reproductive defects in knockout mutants. In female golden hamsters, PIWIL1 and PIWIL3 are highly expressed throughout oogenesis and early embryogenesis, while PIWIL1 knockout leads to sterility, and PIWIL3 deficiency results in subfertility with lagging zygotic development. PIWIL1 can partially compensate for TE silencing and transcriptional regulation in PIWIL3 knockout females, but not vice versa. PIWIL1 and PIWIL4 are the predominant PIWIs expressed in adult or postnatal testes, respectively, while PIWIL2 is present in both stages. Notably, in golden hamsters, none of the differences were found between pre-pachytene and pachytene piRNAs characteristic of mice. Loss of any PIWI expressed in testes leads to sterility and severe but distinct spermatogenesis disorders, which are markedly less severe in mice. These findings expand our understanding of the non-redundant PIWI-piRNA regulatory functions in gametogenesis and early embryogenesis in golden hamster, increasing the value of this model for studying human fertility. Overall design: Using golden hamsters, establish dynamic expression profiles and subcellular localization for all four PIWIs and characterize their associated reproductive defects in knockout mutants.