LENG8

LENG8 is a conserved nuclear RNA quality-control factor that governs the fate of polyadenylated RNPs by directing misprocessed and noncoding transcripts toward nuclear retention and degradation rather than cytoplasmic export (PMID:41861815, PMID:40832163). It assembles with PCID2 and SEM1/DSS1 into a TREX-2-like trimer (variously termed REX or TREX-2.1) that is structurally and functionally equivalent to the canonical GANP-PCID2-SEM1 export complex, but acts as its dominant-negative counterpart: LENG8-PS competes with NPC-associated TREX-2 for UAP56(DDX39B)-bound RNPs and steers them to decay [PMID:40595470, PMID:41861815, PMID:40832163, PMID:bio_10.1101_2025.09.16.676470]. Cryo-EM of the LENG8-containing complex bound to DDX39B revealed a conserved 'trigger loop' in LENG8, analogous to that of GANP, that is critical for regulating release of the DEAD-box ATPase from mRNPs (PMID:40595470). LENG8 is recruited to pre-mRNAs through direct interactions with early splicing factors including the U1 snRNP component U1A and with RRP1B, a feature that distinguishes the LENG8-PCID2 complex from the GANP export complex (PMID:41861815, PMID:40832163, PMID:42140674). Having engaged these substrates, LENG8 couples them to the RNA exosome by recruiting the PAXT adaptor, and its loss causes cytoplasmic leakage of intronically polyadenylated, intron-retained, and noncoding RNAs (PMID:41861815, PMID:40832163, PMID:42140674). This spliceosome-coupled mRNP decay pathway is evolutionarily conserved, with the yeast Thp3-Csn12 module performing the analogous coupling of splicing factors to the nuclear exosome (PMID:42140674).

1. 2025 High

   Established that LENG8 forms a defined nuclear trimeric complex and directly regulates the export ATPase DDX39B, answering how this previously uncharacterized factor engages the mRNA export machinery.

   Evidence Cryo-EM of the LENG8/PCID2/DSS1-DDX39B complex with functional mutagenesis of the LENG8 'trigger loop', plus LENG8 knockdown RNA-seq

   PMID:40595470

   Open questions at the time

   • Whether trigger-loop activity promotes ATPase stimulation or RNP release was defined structurally but not in a reconstituted kinetic assay
   • The set of physiological RNA substrates whose DDX39B handling depends on LENG8 was not exhaustively mapped
2. 2026 High

   Defined LENG8 as a dominant-negative export antagonist and active degradation factor, resolving how it converts an export-like complex into a retention-and-decay machine.

   Evidence LENG8 depletion with transcriptomics, Co-IP, RNA nuclear retention assays and complex reconstitution identifying the REX (LENG8-PCID2-SEM1) complex, U1 snRNP recruitment, and PAXT/exosome coupling

   PMID:40832163 PMID:41861815

   Open questions at the time

   • How LENG8 discriminates misprocessed from correctly processed transcripts at the molecular level is not resolved
   • The stoichiometry and dynamics of competition between LENG8-PS and GANP-PS in cells were not directly measured
3. 2026 High

   Mapped the direct splicing-factor contacts that recruit LENG8-PCID2 to early mRNPs and demonstrated evolutionary conservation, distinguishing the decay connector from the GANP export complex.

   Evidence Biochemical reconstitution, structural analysis and direct pulldown/Co-IP with U1A and RRP1B, plus characterization of the yeast Thp3-Csn12 ortholog pathway

   PMID:42140674

   Open questions at the time

   • The structural basis of U1A and RRP1B binding to LENG8-PCID2 was not determined at high resolution
   • How early spliceosome engagement is temporally coordinated with exosome recruitment is unresolved
4. 2026 Medium

   Showed that PCID2 scaffolds mutually exclusive GANP, LENG8, and SAC3D1 subcomplexes and that LENG8 acts upstream in mRNA processing, framing how a shared scaffold partitions distinct nuclear RNA fates.

   Evidence Interactome characterization, nuclear speckle localization, and LENG8 depletion with mRNA processing and polyadenylation site-usage readout (preprint)

   PMID:42039562

   Open questions at the time

   • Preprint not yet peer-reviewed
   • Mechanism determining which PCID2 subcomplex assembles on a given transcript is unknown
   • The functional role of the SAC3D1-PCID2 subcomplex relative to LENG8 was not defined
5. 2025 Medium

   Provided mechanistic detail that LENG8-PS and GANP-PS compete for the same UAP56-bound RNPs, establishing a competition model for nuclear RNA fate determination.

   Evidence Mutagenesis, transcriptomics and competition assays between PAXT-associated LENG8-PS and NPC-associated TREX-2 modules (preprint)

   PMID:bio_10.1101_2025.09.16.676470

   Open questions at the time

   • Preprint not yet peer-reviewed
   • The kinetic parameters governing the competition outcome were not quantified
   • How spatial separation (nucleoplasm vs NPC) biases the competition in vivo is not directly shown

• How LENG8 distinguishes correctly processed from aberrant transcripts and what controls the partitioning of substrates between export and decay remains the central open question.
• No molecular discriminator of 'misprocessed' RNA defined
• Regulation of LENG8-PS versus GANP-PS abundance and localization in different conditions is unknown
• Physiological consequences of LENG8 loss at the organismal level not characterized in the corpus