LENG8

LENG8 is a conserved nuclear RNA quality-control factor that enforces retention and degradation of misprocessed mRNAs and noncoding RNAs. It is recruited to pre-mRNAs by splicing factors including U1 snRNP and assembles with PCID2 and SEM1/DSS1 into the REX (TREX-2.1) complex, which is structurally analogous to the canonical TREX-2 export complex but acts as its dominant-negative antagonist: a conserved trigger loop in LENG8 releases DDX39B (UAP56) from mRNPs, diverting polyadenylated transcripts away from nuclear export (PMID:40595470, PMID:41861815). LENG8 localizes to nuclear speckles and promotes degradation of retained RNAs by directly recruiting the PAXT–nuclear exosome pathway; loss of LENG8 results in cytoplasmic leakage of intron-retained, intronically polyadenylated, and noncoding RNAs (PMID:41861815, PMID:40595470).

1. 2025 High

   Structural determination of the LENG8–PCID2–DSS1 (TREX-2.1) complex revealed how LENG8 uses a trigger loop to release DDX39B from mRNPs, establishing LENG8 as a direct regulator of mRNP remodeling analogous to GANP in canonical TREX-2.

   Evidence Cryo-EM structure of TREX-2.1/DDX39B complex with trigger-loop mutagenesis and RNA-seq in knockdown cells

   PMID:40595470

   Open questions at the time

   • Substrate specificity beyond GC-content enrichment is not defined
   • Whether trigger-loop activity is regulated by post-translational modifications is unknown
   • No in vivo reconstitution of the full retention-to-degradation pathway
2. 2026 High

   Characterization of the REX complex demonstrated that LENG8 serves dual, coupled roles — nuclear retention via dominant-negative competition with TREX-2 and RNA degradation via direct recruitment of PAXT and the nuclear exosome — thereby establishing LENG8 as a central checkpoint factor for misprocessed and noncoding RNA disposal.

   Evidence Biochemical reconstitution of the REX complex, siRNA knockdown with RNA-seq, genetic epistasis with TREX-2 and exosome components (Molecular Cell)

   PMID:41861815

   Open questions at the time

   • How selectivity for misprocessed versus correctly processed mRNAs is achieved at the molecular level is unresolved
   • Whether LENG8 functions redundantly with other nuclear retention factors is not tested
   • Direct structural basis for the LENG8–PAXT interaction has not been determined
3. 2026 Medium

   Localization and interactome studies placed LENG8 at nuclear speckles — distinct from the nuclear-envelope residence of GANP-containing TREX-2 — and showed that LENG8 depletion alters polyadenylation site usage, positioning REX upstream of TREX-2 in the mRNA processing hierarchy.

   Evidence Immunofluorescence for subcellular localization, interactome analysis, siRNA knockdown with poly(A)-site usage profiling (preprint)

   PMID:42039562

   Open questions at the time

   • Preprint; not yet peer-reviewed
   • Mechanism by which nuclear speckle localization is achieved is unknown
   • Whether polyadenylation site changes are a direct or indirect consequence of LENG8 depletion is unclear

• Key unresolved questions include the molecular basis for selective recognition of misprocessed transcripts, the structural interface between REX and PAXT, and whether LENG8 loss contributes to disease through aberrant cytoplasmic accumulation of noncoding or intron-containing RNAs.
• No disease association has been established for LENG8
• No structural model of the full LENG8–PAXT interface exists
• In vivo physiological consequences of LENG8 loss in animal models have not been reported