The meiRNA (1–508 nt) was used for in vitro CLIP–seq experiments. The RNA was transcribed and purified in vitro (Lv et al., 2019 (link)). The DNA template used to transcribe the meiRNA was synthesized by TaKaRa Bio Inc. and dissolved in DEPC-treated water to a final concentration of 100 mM. The reaction mixture comprised 10 mM Tris, 10 mM DTT, 10 mM NTPs, 40 mM MgCl2, 0.3 mM T7 template, 0.3 mM DNA templates, and 3 mg/ml T7 polymerase. The reaction was performed at 37°C for 4 h. After transcription, the transcription products were treated with 0.1 total volume (0.1 V) of 0.5 M EDTA, 0.1 V of 5 M NaCl, and 3 V of absolute alcohol and incubated at −40°C overnight. The transcription products were then centrifuged, the supernatant was discarded, and the precipitated RNA was dissolved in 1.5 ml of DEPC-treated water. An equal volume of RNA loading buffer (TaKaRa Bio Inc.) was added, and the mixture was incubated at 90°C for 5 min and cooled on ice for 5 min. The RNA samples were separated on a 12% denaturing polyacrylamide gel and purified using Elutrap (Whatman). The final meiRNA was dialyzed against DEPC-treated water and stored at −80°C.