C19ORF84 connects piRNA and DNA methylation machineries to defend the mammalian germ line

In the male mouse germline, PIWI-interacting RNAs (piRNAs) bound to the PIWI protein MIWI2 guide the DNA methylation of young active transposable elements (TEs) through SPOCD1. We identified loss-of-function variants in the human SPOCD1 gene that cause male infertility and defective TE silencing. One of the SPOCD1 pathogenic alleles encodes a truncated protein that lacks the conserved carboxy-terminus. We discovered that this deleted region interacts with C19ORF84. In mouse foetal germ cells, C19ORF84 is a nuclear protein that is required for the association of SPOCD1 with DNMT3L, an essential component of the de novo methylation machinery. In summary, we found a conserved role for SPOCD1 in safeguarding the continuity of the human germline and discovered C19ORF84, an uncharacterised protein essential for orchestrating piRNA-directed DNA methylation. Examination of piRNA expression profiles in control (C19orf84+/-) and C19orf84-/- foetal testes as well as RNA expression profiles in wild-type and C19orf84-/- P20 testis.