Affinage

SCML2

Sex comb on midleg-like protein 2 · UniProt Q9UQR0

Length
700 aa
Mass
77.3 kDa
Annotated
2026-06-10
15 papers in source corpus 15 papers cited in narrative 15 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SCML2 is a germline-enriched Polycomb protein that establishes distinct chromatin states in the male germline through opposing control of histone H2A ubiquitination (PMID:25703348). On autosomes it promotes RNF2-dependent H2AK119 ubiquitination to repress somatic and progenitor genes, while on the meiotic sex chromosomes it recruits the deubiquitinase USP7 to the XY body and suppresses H2A ubiquitination, producing two antithetical epigenetic programs (PMID:25703348, PMID:25634095). Through USP7 it bridges to PRC1.4 and stabilizes BMI1, coupling deubiquitinase activity to maintenance of functional PRC1 and appropriate repressive H2Aub levels (PMID:25605328). SCML2 is targeted to hypomethylated, H3K4me2/3-rich promoters where it facilitates PRC2-mediated H3K27me3 deposition and builds bivalent chromatin domains on developmental and somatic gene classes (PMID:29686098), and it organizes pericentromeric heterochromatin by suppressing PRC1-mediated H2AK119ub while promoting H3K27me3 (PMID:30097555). Chromatin targeting is multivalent, integrating MBT-domain recognition of monomethylated lysine (PMID:18706910), sequence-specific double-stranded DNA binding by the SLED domain (PMID:24727478), an RNA-binding region engaging ncRNAs, and SPM-domain-mediated PRC1 association (PMID:24986859). The H3K27me3 deposited by SCML2 on bivalent promoters in sperm transmits paternal epigenetic information to offspring (PMID:37283086). Beyond the germline, the nucleoplasmic isoform SCML2B forms inhibitory complexes with CDK/CYCLIN and p21/p27 to restrain G1/S progression (PMID:24358021), and SCML2 functions in the DNA-damage response, where CHK1-mediated phosphorylation stabilizes it and its competition with p53 for USP7 binding influences chemoresistance (PMID:37353627).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 2008 High

    Established the structural basis by which SCML2 reads histone methylation, defining a molecular recognition module before its in vivo Polycomb role was known.

    Evidence NMR and X-ray crystallography with histone peptide binding assays on human SCML2 MBT repeats

    PMID:18706910

    Open questions at the time
    • Did not establish which methylated histone marks are physiological targets in cells
    • No link to chromatin localization or gene regulation
  2. 2013 High

    Showed that the nucleoplasmic isoform SCML2B has a cell-cycle function distinct from chromatin regulation, directly coupling SCML2 to CDK inhibition.

    Evidence Protein purification, Co-IP, in vitro kinase assays and cell-cycle analysis of SCML2B/CDK/CYCLIN/p21/p27 complexes

    PMID:24358021

    Open questions at the time
    • Physiological context where SCML2B cell-cycle control operates not defined
    • Relationship to germline chromatin functions unclear
  3. 2014 High

    Defined how SCML2A is recruited to chromatin, identifying RNA binding and SPM-PRC1 interaction as coordinated targeting determinants.

    Evidence Domain deletion mutagenesis, ChIP and RNA-binding assays with overexpression rescue

    PMID:24986859

    Open questions at the time
    • Identity of the targeting ncRNAs not resolved
    • Quantitative contribution of each domain to targeting not separated
  4. 2014 Medium

    Identified the SLED domain as a sequence-specific dsDNA-binding module, providing a candidate mechanism linking SCML2/PRC1 to specific promoters.

    Evidence Solution NMR structure determination with in vitro DNA-binding assays

    PMID:24727478

    Open questions at the time
    • No in vivo validation of sequence-specific DNA binding in this study
    • Target sequence preferences not mapped genome-wide
  5. 2015 High

    Revealed the central paradox of SCML2 biology: it is a germline PRC1 subunit that both promotes H2A ubiquitination on autosomes and prevents it on sex chromosomes during meiosis.

    Evidence Knockout mouse, ChIP-seq and histone modification analysis

    PMID:25703348

    Open questions at the time
    • Mechanism distinguishing autosomal vs sex-chromosome behavior not fully resolved
    • Downstream consequences for fertility partially defined
  6. 2015 High

    Explained the sex-chromosome arm of the paradox by showing SCML2 recruits the deubiquitinase USP7 to the XY body and that USP7 bridges to PRC1.4 to regulate RING1B/BMI1 status.

    Evidence Reciprocal Co-IP, immunofluorescence in KO spermatocytes, ChIP, USP7 inhibition and protein stability assays

    PMID:25605328 PMID:25634095

    Open questions at the time
    • What restricts USP7 recruitment to sex chromosomes versus autosomes not defined
    • Catalytic mechanism of selective deubiquitination on chromatin not reconstituted
  7. 2018 High

    Placed SCML2 within an ordered germline pathway, showing it facilitates PRC2-mediated H3K27me3 at bivalent promoters and acts in epistasis with RNF8 to control the ubiquitin-to-acetylation switch.

    Evidence ChIP-seq and genetic epistasis with Scml2 and Rnf8 mutant mice across multiple histone marks

    PMID:29462142 PMID:29686098 PMID:30097555

    Open questions at the time
    • How SCML2 selects bivalent versus monovalent targets not resolved
    • Direct mechanism coupling H2Aub removal to acetylation not biochemically reconstituted
  8. 2019 Medium

    Identified a rapidly evolved DNA-binding repeat module (SDB) that, with the RNA-binding region, lets SCML2 sense DNA hypomethylation for target locus binding.

    Evidence Domain deletion mutagenesis, ChIP-seq, evolutionary and DNA methylation correlation analysis in mouse

    PMID:30137219

    Open questions at the time
    • Direct mechanism of hypomethylation sensing not reconstituted in vitro
    • Conservation of this module beyond rodents not established
  9. 2023 High

    Demonstrated that SCML2-dependent H3K27me3 in sperm is heritable, establishing a route for paternal epigenetic inheritance into offspring.

    Evidence Assisted reproduction with testicular sperm, sperm ChIP-seq, and transcriptomics in F1 offspring from Scml2-KO-derived germ cells

    PMID:37283086

    Open questions at the time
    • Persistence of inherited marks beyond preimplantation embryos not defined
    • Phenotypic consequences in adult offspring not characterized
  10. 2023 Medium

    Extended SCML2 function to the DNA-damage response and cancer, showing CHK1-dependent phosphorylation stabilizes SCML2 and that it tunes p53, CHK1 and p21 stability via USP7 competition.

    Evidence Co-IP, site-specific mutagenesis (Ser570, Ser441), ubiquitination and kinase assays, viability after DNA damage; separately YAP1 interaction by Co-IP/MS/PLA/GST pulldown

    PMID:37353627 PMID:37810219

    Open questions at the time
    • Generality of chemoresistance mechanism across tumor types not established
    • Functional consequence of the SCML2-YAP1 interaction incompletely defined
  11. 2025 Low

    Tested whether SCML2 drives Polycomb spreading at hypomethylated pericentromeric heterochromatin in stem cells, finding it dispensable in this context.

    Evidence Inducible Dnmt1 knockdown mESC model with ChIP-seq for H2AK119ub1 and H3K27me3 in SCML2-depleted cells (preprint)

    PMID:bio_10.1101_2025.11.14.688451

    Open questions at the time
    • Negative result in a single ESC context; not independently confirmed
    • Does not address germ-cell PCH role where SCML2 functions

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unresolved how SCML2's multivalent targeting modules are integrated to dictate the autosome-versus-sex-chromosome and bivalent-versus-monovalent decisions in vivo.
  • No reconstituted model linking MBT, SLED/SDB DNA binding, RNA binding and SPM-PRC1 contacts to locus selection
  • Mechanism switching SCML2 between ubiquitin-promoting and ubiquitin-suppressing modes unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 3 GO:0098772 molecular function regulator activity 3 GO:0003677 DNA binding 2 GO:0003723 RNA binding 2 GO:0042393 histone binding 1
Localization
GO:0005694 chromosome 3 GO:0005634 nucleus 1 GO:0005654 nucleoplasm 1
Pathway
R-HSA-4839726 Chromatin organization 4 R-HSA-1474165 Reproduction 2 R-HSA-74160 Gene expression (Transcription) 2 R-HSA-1640170 Cell Cycle 1 R-HSA-73894 DNA Repair 1
Partners
BMI1CDK2P21P27P53RNF2USP7YAP1
Complex memberships
PRC1PRC1.4 (BMI1-containing)SCML2-USP7 complexSCML2B-CDK/CYCLIN/p21/p27 complex

Evidence

Reading pass · 15 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2015 SCML2 is a germline-specific subunit of PRC1 that promotes RNF2-dependent ubiquitination of H2A on autosomes (marking somatic/progenitor genes for repression) while paradoxically preventing RNF2-dependent H2A ubiquitination on sex chromosomes during meiosis, establishing distinct epigenetic programs through two antithetical mechanisms. Genetic knockout mouse model, ChIP-seq, histone modification analysis Developmental Cell High 25703348
2015 SCML2 interacts with and recruits the deubiquitinase USP7 to the XY body in spermatocytes; in the absence of SCML2, USP7 fails to accumulate on the XY body and H2A monoubiquitination is dramatically augmented in XY chromatin, establishing SCML2/USP7 as a complex that modulates epigenetic state of sex chromosomes during male meiosis. Co-immunoprecipitation, immunofluorescence in knockout mouse spermatocytes, histone modification analysis PLoS Genetics High 25634095
2015 USP7 bridges with PRC1.4 (BMI1-containing) via SCML2; SCML2 modulates USP7 localization and stabilizes BMI1 through USP7-mediated deubiquitination. USP7 catalytic activity is required to maintain functional PRC1 and appropriate levels of repressive H2Aub, regulating the post-translational status of RING1B and BMI1. Co-immunoprecipitation, ChIP, USP7 inhibition, protein stability assays Molecular and Cellular Biology High 25605328
2014 SCML2A (chromatin-bound isoform) binds PRC1 via its SPM domain and interacts with ncRNAs through a novel RNA-binding region (RBR); deletion of the RBR reduces SCML2A occupancy at target genes and overexpression of RBR-deleted SCML2A causes defects in PRC1 recruitment, indicating coordinated action of MBT domains, RNA binding, and SPM-PRC1 interaction for chromatin targeting. Domain deletion mutagenesis, ChIP, RNA-binding assays, overexpression rescue experiments eLife High 24986859
2013 SCML2B (nucleoplasmic isoform) forms a stable complex with CDK/CYCLIN/p21 and p27, enhancing p21/p27 inhibitory effect; SCML2B stabilizes p21 and favors its interaction with CDK2/CYCE, reducing kinase activity and inhibiting G1/S progression. CDK/CYCLIN complexes in turn phosphorylate SCML2, and CDK2 interaction with SCML2B is regulated through the cell cycle. Protein purification, Co-immunoprecipitation, kinase activity assays, cell-cycle analysis, CDK2-SCML2B interaction through cell cycle PLoS Biology High 24358021
2008 The two MBT repeat domains of human SCML2 preferentially bind histone peptides monomethylated at lysine residues with no apparent sequence specificity; crystal structure reveals that monomethyllysine binds an aromatic-rich pocket at one end of the beta-barrel of the second MBT repeat. NMR spectroscopy, X-ray crystallography, peptide binding assays Journal of Molecular Biology High 18706910
2014 A conserved domain within human SCML2, termed SLED (Scm-like embedded domain), adopts a novel α/β fold and binds double-stranded DNA in a sequence-specific manner as determined by solution NMR, potentially linking PRC1 complexes to target gene promoters. Solution NMR spectroscopy, DNA-binding assays Journal of Biological Chemistry Medium 24727478
2018 SCML2 binds to H3K4me2/3-rich hypomethylated promoters in undifferentiated spermatogonia to facilitate PRC2-mediated H3K27me3 deposition, establishing bivalent chromatin domains on two classes of genes: developmental regulator genes silent throughout spermatogenesis (Class I) and somatic genes silenced during late spermatogenesis (Class II). ChIP-seq in Scml2 knockout mice, genome-wide bivalency mapping PNAS High 29686098
2018 RNF8 and SCML2 cooperate in ubiquitin regulation during meiosis: SCML2 deubiquitinates RNF8-independent H2AK119ub but does not deubiquitinate RNF8-dependent polyubiquitination; RNF8-dependent polyubiquitination is required for H3K27 acetylation (active enhancer mark), while persistent H2AK119ub inhibits H3K27 acetylation establishment, followed by H3K4 dimethylation on poised promoters. Double mutant (Rnf8 and Scml2) genetic epistasis, ChIP-seq, histone modification analysis PLoS Genetics High 29462142
2018 SCML2 accumulates on pericentromeric heterochromatin (PCH) in male germ cells, suppresses PRC1-mediated H2AK119ub and promotes PRC2-mediated H3K27me3 during meiosis; loss of SCML2 in postmeiotic spermatids leads to ectopic facultative heterochromatin patches driven by ectopic somatic lamin expression, and impairs CENP-V localization on PCH. Immunofluorescence, ChIP-seq in Scml2 KO mice, heterochromatin marker analysis, CENP-V localization Journal of Cell Science High 30097555
2019 Mouse SCML2 contains a novel, rapidly evolved domain termed SDB (SCML2 DNA-binding) repeats comprising 28-amino-acid repeat units that undergo positive selection in rodents; these cooperate with the RNA-binding region to recruit SCML2 to hypomethylated chromatin, enabling SCML2 to sense DNA hypomethylation in vivo for target locus binding. Domain deletion mutagenesis, ChIP-seq, evolutionary analysis, DNA methylation correlation Biology of Reproduction Medium 30137219
2023 SCML2 is required for H3K27me3 deposition on bivalent promoters in testicular sperm; loss of SCML2 in F0 males causes dysregulation of SCML2-target genes in wild-type F1 male germline during spermiogenesis and in F1 preimplantation embryos, establishing that Polycomb-mediated H3K27me3 in sperm mediates paternal epigenetic inheritance. Assisted reproductive technology with testicular sperm, ChIP-seq of testicular and epididymal sperm, F1 gene expression analysis in Scml2-KO-derived wild-type offspring Nucleic Acids Research High 37283086
2023 DNA damage stabilizes SCML2 through CHK1-mediated phosphorylation at Ser570; SCML2 binds the TRAF domain of USP7 (with Ser441 critical for interaction) and in p53-positive cells competes with p53 for USP7 binding to destabilize p53, promoting chemoresistance; in p53-negative cells, SCML2 promotes CHK1 and p21 stability by inhibiting their ubiquitination. SCML2A primarily stabilizes CHK1, while SCML2B regulates p21 stability. Co-immunoprecipitation, mutagenesis (Ser570, Ser441), ubiquitination assays, kinase assays, cell viability after DNA damage Cell Death and Differentiation Medium 37353627
2023 SCML2 physically interacts with YAP1 as demonstrated by co-immunoprecipitation, mass spectrometry, proximity ligation assay, and GST pulldown; androgen regulates this interaction in human tumor cell models, and silencing SCML2 alters cell growth behavior in response to androgen signaling. Co-immunoprecipitation, mass spectrometry, proximity ligation assay, GST pulldown, RNAi knockdown with growth assays iScience Medium 37810219
2025 Neither PRC1 nor PRC2 recruitment to hypomethylated pericentromeric heterochromatin depends on SCML2 in mouse embryonic stem cells, as demonstrated in a doxycycline-inducible Dnmt1 model; this is a negative result specifically for SCML2's role in Polycomb spreading at hypomethylated PCH in ESCs. Inducible Dnmt1 knockdown mESC model, ChIP-seq for H2AK119ub1 and H3K27me3 in SCML2-depleted cells bioRxivpreprint Low bio_10.1101_2025.11.14.688451

Source papers

Stage 0 corpus · 15 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2015 SCML2 establishes the male germline epigenome through regulation of histone H2A ubiquitination. Developmental cell 119 25703348
2018 Polycomb protein SCML2 facilitates H3K27me3 to establish bivalent domains in the male germline. Proceedings of the National Academy of Sciences of the United States of America 72 29686098
2015 Polycomb protein SCML2 associates with USP7 and counteracts histone H2A ubiquitination in the XY chromatin during male meiosis. PLoS genetics 66 25634095
2018 RNF8 and SCML2 cooperate to regulate ubiquitination and H3K27 acetylation for escape gene activation on the sex chromosomes. PLoS genetics 48 29462142
2015 USP7 cooperates with SCML2 to regulate the activity of PRC1. Molecular and cellular biology 46 25605328
2014 Interactions with RNA direct the Polycomb group protein SCML2 to chromatin where it represses target genes. eLife 42 24986859
1999 Identification of SCML2, a second human gene homologous to the Drosophila sex comb on midleg (Scm): A new gene cluster on Xp22. Genomics 36 10331946
2008 The malignant brain tumor repeats of human SCML2 bind to peptides containing monomethylated lysine. Journal of molecular biology 31 18706910
2018 SCML2 promotes heterochromatin organization in late spermatogenesis. Journal of cell science 28 30097555
2013 Polycomb protein SCML2 regulates the cell cycle by binding and modulating CDK/CYCLIN/p21 complexes. PLoS biology 25 24358021
2023 Polycomb protein SCML2 mediates paternal epigenetic inheritance through sperm chromatin. Nucleic acids research 15 37283086
2023 SCML2 contributes to tumor cell resistance to DNA damage through regulating p53 and CHK1 stability. Cell death and differentiation 9 37353627
2014 Solution NMR structure of the DNA-binding domain from Scml2 (sex comb on midleg-like 2). The Journal of biological chemistry 7 24727478
2019 A rapidly evolved domain, the SCML2 DNA-binding repeats, contributes to chromatin binding of mouse SCML2†. Biology of reproduction 3 30137219
2023 Discordant interactions between YAP1 and polycomb group protein SCML2 determine cell fate. iScience 1 37810219

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