Paternal pachytene piRNAs are not required for fertilization, embryonic development and sperm-mediated epigenetic inheritance in mice
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Pachytene piRNAs areMIWI-/MILI-bound small RNAs abundantly expressed in pachytene spermatocytes and round spermatids in adultmouse testes. Miwi knockout (KO) male mice are sterile due to spermiogenic arrest. In Caenorhabditis elegans, sperm-borne piRNAs appear to have an epigenetic role during fertilization and development because progeny of individuals with piRNA-deficient gametes display a progressive loss of fertility after several generations. Inmice, it remains unknown whether pachytene piRNA-deficient round spermatids can produce offspring, and whether the progeny of Miwimutants also exhibits transgenerational, progressive fertility loss. Here, we report that Miwi KO round spermatids could fertilize both wild-type (WT) and Miwi KO oocytes through round spermatid injection, and could produce healthy and fertile offspring despite the global downregulation of both MIWI-/MILI-bound pachytene piRNAs. Progeny of ROSI-derived heterozygotes, bothmale and female, displayed normal fertility for at least three generations when bred with either WT or Miwi KO females. Our data indicate that aberrant MIWI-/MILI-bound pachytene piRNA profiles in spermatids do not affect fertilization, early embryonic development, or fertility of the offspring, suggesting that pachytene piRNAs might not be required for paternal transgenerational epigenetic inheritance inmice.