FBS Colloquia No.397Germline Biology Group

Suppressing transposon mobilization in animal germ cells is essential for the faithful transmission of genomic information to the next generation. A highly conserved mechanism underlying this suppression, from fruit flies to mammals, is the piRNA (Piwi-interacting RNA) pathway. In this pathway, small RNAs known as piRNAs form complexes with PIWI family proteins. These complexes mediate transcriptional silencing in the nucleus and, in the cytoplasm, localize to non-membranous organelles called nuage, where they specifically cleave and degrade transposon mRNAs with complementary sequences. Disruption of the piRNA pathway leads to germ cell defects and infertility. Numerous proteins, including PIWI family proteins, function cooperatively within this pathway. Post-translational modifications are critical for this cooperation—Tudor domain proteins bind to the dimethylated N-termini of PIWI proteins and promote the assembly of nuage.

Functional analysis of the ubiquitination activity of Drosophila Kumo and its physiological role

The RING domain functions as an E3 ubiquitin ligase that catalyzes protein ubiquitination, a key post-translational modification. Among all identified piRNA pathway proteins, Kumo is unique in containing a RING domain. This suggests that Kumo may regulate other piRNA pathway components through its ubiquitin ligase activity. We investigated Kumo's function using RING domain mutants, in vitro ubiquitination assays, and pull-down experiments to identify ubiquitination targets. In this colloquium, we will discuss Kumo's regulatory role in the piRNA pathway based on our findings.

Post-translational modifications of piRNA pathway factors that safeguard the germline genome

Neddylation, another type of post-translational modification, is known to be indispensable for mammalian embryonic development; however, its roles in oogenesis and in the piRNA pathway remain unknown. In this study, we used mass spectrometry to identify candidate substrates of neddylation. In this colloquium, I will present our current findings and discuss future perspectives on how neddylation may contribute to piRNA pathway regulation.