L3MBTL2

L3MBTL2 is a component of the non-canonical polycomb repressive complex PRC1.6 that participates in promoter-specific transcriptional silencing [PMID:bio_10.1101_2024.07.12.603173]. It co-localizes with the HUSH complex on chromatin, primarily at active promoters, and contributes to HUSH-mediated silencing of proviruses, with PRC1.6 recruitment at a subset of HUSH-silenced genes depending on the core HUSH component MPP8 [PMID:bio_10.1101_2024.07.12.603173]. Beyond this single preprint observation, no further mechanistic detail on L3MBTL2 has been characterized in the available corpus.

1. 2024 Low

   It was unknown how the non-canonical PRC1.6 complex coordinates with the HUSH silencing machinery; proximity labeling and chromatin profiling established that L3MBTL2/PRC1.6 co-localizes with HUSH at active promoters and that its binding at a subset of targets requires the HUSH component MPP8.

   Evidence proximity labeling (C-BERST/dCas9-APEX2), forward genetic screen, genome-wide chromatin co-localization, and loss-of-function analysis in human cells (preprint)

   PMID:bio_10.1101_2024.07.12.603173

   Open questions at the time

   • Single preprint without in vitro reconstitution or direct biochemical interaction assay between L3MBTL2 and HUSH components
   • Mechanism by which MPP8 recruits PRC1.6 to chromatin is not defined
   • No direct demonstration that L3MBTL2 itself, rather than the broader PRC1.6 complex, mediates the silencing

• Whether L3MBTL2 directly contacts HUSH components and the molecular basis of its promoter-specific silencing activity remain unresolved.
• No reconstituted biochemistry defining L3MBTL2-HUSH contacts
• No structural model of PRC1.6 engagement with HUSH-silenced promoters