Cell Reports (Feb 2023)

Promiscuous splicing-derived hairpins are dominant substrates of tailing-mediated defense of miRNA biogenesis in mammals

  • Seungjae Lee,
  • David Jee,
  • Sid Srivastava,
  • Acong Yang,
  • Abhinav Ramidi,
  • Renfu Shang,
  • Diane Bortolamiol-Becet,
  • Sébastien Pfeffer,
  • Shuo Gu,
  • Jiayu Wen,
  • Eric C. Lai

Journal volume & issue
Vol. 42, no. 2
p. 112111

Abstract

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Summary: Canonical microRNA (miRNA) hairpins are processed by the RNase III enzymes Drosha and Dicer into ∼22 nt RNAs loaded into an Argonaute (Ago) effector. In addition, splicing generates numerous intronic hairpins that bypass Drosha (mirtrons) to yield mature miRNAs. Here, we identify hundreds of previously unannotated, splicing-derived hairpins in intermediate-length (∼50–100 nt) but not small (20–30 nt) RNA data. Since we originally defined mirtrons from small RNA duplexes, we term this larger set as structured splicing-derived RNAs (ssdRNAs). These associate with Dicer and/or Ago complexes, but generally accumulate modestly and are poorly conserved. We propose they contaminate the canonical miRNA pathway, which consequently requires defense against the siege of splicing-derived substrates. Accordingly, ssdRNAs/mirtrons comprise dominant hairpin substrates for 3′ tailing by multiple terminal nucleotidyltransferases, notably TUT4/7 and TENT2. Overall, the rampant proliferation of young mammalian mirtrons/ssdRNAs, coupled with an inhibitory molecular defense, comprises a Red Queen’s race of intragenomic conflict.

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