show Abstracthide AbstractPIWI-interacting RNAs (piRNAs) are small RNAs that play a critical role in repressing transposons in the germline by guiding PIWI proteins to complementary target sequences. It is well known that the 5' ends of piRNAs are typically defined through cleavage by PIWI proteins or by the endonuclease Zucchini, and that piRNAs are amplified via reciprocal cleavage of sense and antisense transcripts by PIWI proteins. Here, we show that low levels of sense-stranded piRNAs are produced from the whole transcriptome in silkworms. To examine the requirement of Zuc in the production of gene-derived sense piRNAs, we investigated the change in their expression upon the knockdown (KD) of Zuc.