library_construction_protocol: Human fetal testes small RNAs from NTU cohort were extracted from abortus gonads using miRNeasy Tissue/Cells Advanced Kits (Cat.217684; Qiagen). Library construction was performed using illumina Truseq Small RNA Sample Prep Kit, with the 2013 version composing all small RNAs, inculding microRNAs and larger small RNAs falling into piRNA criteria of 24-34 nt long. In the 2014 version of sequencing analysis, we enriched the proportion of piRNA sequencing reads by actively reducing a significant portion of inserting small RNAs below 22 nt via gel excision during sequencing library preparation.