QSER1

QSER1 is a chromatin-associated epigenetic regulator that safeguards the transcriptional and developmental programs of pluripotent stem cells by protecting key cis-regulatory regions from aberrant de novo DNA methylation (PMID:33833093). A genome-wide CRISPR screen in human embryonic stem cells identified QSER1 as the top regulator of DNA methylation, where it cooperates genetically and biochemically with TET1 to protect bivalent promoters, poised enhancers, and DNA methylation valleys from DNMT3-mediated methylation (PMID:33833093), and extends this protection to a distinct class of distal transcriptionally competent chromatin regions (PMID:37398096). At lineage-specific loci QSER1 acts as a transcriptional brake: it is recruited to YAP1:TEAD4 enhancers and blocks RNA Polymerase II recruitment, so that its loss—like YAP1 loss—derepresses NODAL and produces hyperactive NODAL signaling in human gastruloids (PMID:41888256). QSER1 additionally partners with SIN3A to occupy cis-regulatory elements of pro-apoptotic genes such as PUMA, where it antagonizes p53-driven transcription and restrains apoptosis (PMID:36371602). Consistent with these developmental roles, QSER1 is enriched in the chromatome of ground and formative pluripotency states (PMID:36806742), and heterozygous loss-of-function variants in humans are associated with neurodevelopmental phenotypes (PMID:41139957).

1. 2021 High

   Established QSER1 as a principal guardian of the DNA methylation landscape in pluripotent cells, answering whether a dedicated factor protects developmental regulatory regions from de novo methylation.

   Evidence Genome-wide CRISPR-Cas9 screen with a knockin methylation reporter in hESCs, plus genetic epistasis and biochemical interaction with TET1

   PMID:33833093

   Open questions at the time

   • Molecular basis by which QSER1 recognizes or is recruited to methylation valleys not resolved
   • Direct enzymatic activity, if any, of QSER1 undefined
   • Structural basis of the QSER1-TET1 interaction not determined
2. 2022 High

   Showed QSER1 actively restrains apoptosis by silencing pro-apoptotic genes, revealing a transcriptional repressive role distinct from methylation protection.

   Evidence ChIP-seq mapping of QSER1 and p53 occupancy, CRISPR deletion of the QBP element at PUMA, siRNA knockdown with apoptosis readout, and Co-IP with SIN3A

   PMID:36371602

   Open questions at the time

   • How QSER1 selects pro-apoptotic target loci is unknown
   • Mechanism linking SIN3A recruitment to p53 antagonism not defined
   • Whether the PUMA QBP behavior generalizes across all pro-apoptotic targets unestablished
3. 2023 Medium

   Extended QSER1/TET1 methylation protection to a previously uncharacterized class of distal transcriptionally competent chromatin regions, and placed QSER1 in the pluripotency chromatome.

   Evidence CRISPR-activation screens with methylation and chromatin accessibility readouts (preprint); ChAC-DIA-MS chromatin proteomics across pluripotency states

   PMID:36806742 PMID:37398096

   Open questions at the time

   • CCR findings derive from a single-lab preprint
   • Functional consequence of QSER1 enrichment in ground/formative states not directly tested
   • Relationship between CCRs and previously defined bivalent/valley regions unclear
4. 2025 Medium

   Defined a mechanistic link between Hippo/YAP signaling and QSER1-mediated repression, showing QSER1 enforces a Pol II block at lineage enhancers to restrain NODAL signaling.

   Evidence Proximity labeling and Co-IP in human pluripotent stem cells, QSER1 depletion with scRNA-seq, and CUT&RUN/ChIP for TEAD4 and Pol II occupancy in 2D-gastruloids

   PMID:41888256

   Open questions at the time

   • Direct physical contact between QSER1 and the YAP1:TEAD4 complex versus indirect recruitment not fully resolved
   • How QSER1 mechanistically blocks Pol II recruitment unknown
   • Single-lab study
5. 2025 Low

   Connected QSER1 dosage to human neurodevelopment, addressing whether its molecular functions have an organismal phenotype.

   Evidence Trio sequencing identifying de novo loss-of-function variants, minigene splice assay, and in situ hybridization of qser1 in zebrafish embryos

   PMID:41139957

   Open questions at the time

   • No direct mechanistic rescue experiment linking variants to QSER1 chromatin function
   • Causality from association alone is limited
   • Neural phenotype inferred from expression pattern, not functional perturbation

• The molecular mechanism by which QSER1 senses unmethylated chromatin and physically excludes DNMT3, blocks Pol II, or recruits its partners remains undefined.
• No structural model of QSER1 or its chromatin-binding mode
• No defined catalytic or domain-level activity
• Recruitment logic distinguishing protective versus repressive targets unknown