A nowhere-to-hide mechanism ensures complete piRNA-directed LINE1 methylation

ABSTRACT: The mouse PIWI-interacting RNA (piRNA) pathway provides anti-transposon immunity to the developing male germline by directing transposon DNA methylation. The first step in this process is the recruitment of SPOCD1 to young LINE1 loci 1 followed in the second step by piRNA-mediated tethering of the PIWI protein MIWI2 (PIWIL4) to the nascent transposon transcript. To protect the germline, the piRNA pathway needs to methylate all active transposon copies but how this is achieved remains unknown. Here, we show that nuclear piRNA and de novo methylation factors are all euchromatic. We find that SPOCD1 directly interacts with the nuclear pore component TPR, which forms heterochromatin exclusion zones adjacent to nuclear pores. In foetal gonocytes undergoing piRNA-directed DNA methylation, TPR is found both at the nuclear periphery but also abundantly throughout the nucleoplasm. We found that the SPOCD1-TPR interaction is required for complete non-stochastic piRNA-directed LINE1 methylation. The loss of the SPOCD1-TPR interaction results in a fraction of SPOCD1 and other chromatin-bound piRNA factors to relocalise to constitutive heterochromatin where they are no longer accessible to MIWI2 and the de novo methylation machinery. We propose that TPR-mediated heterochromatin exclusion provides a nowhere-to-hide mechanism for SPOCD1-bound LINE1 loci throughout the nucleoplasm. In summary, the piRNA pathway has co-opted TPR to guarantee LINE1s are euchromatic and accessible to the piRNA and de novo methylation machineries.

INSTRUMENT(S):

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Testis, Embryonic Stem Cell

SUBMITTER: Christos Spanos  

LAB HEAD: Donal O' Carroll

PROVIDER: PXD060850 | Pride | 2025-11-11

REPOSITORIES: Pride