Affinage

SCML2

Sex comb on midleg-like protein 2 · UniProt Q9UQR0

Length
700 aa
Mass
77.3 kDa
Annotated
2026-04-28
15 papers in source corpus 15 papers cited in narrative 15 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SCML2 is a germline-enriched Polycomb group protein that functions as a context-dependent epigenetic regulator of histone H2A ubiquitination and H3K27 trimethylation during spermatogenesis and cell cycle control. On autosomes, the chromatin-bound SCML2A isoform associates with PRC1 via its SPM domain and promotes RNF2-dependent H2AK119 ubiquitination to repress somatic genes, while on sex chromosomes it recruits the deubiquitinase USP7 to remove H2AK119ub, enabling a distinct epigenetic state required for meiotic sex chromosome inactivation (PMID:25703348, PMID:25634095, PMID:29462142). SCML2 binds hypomethylated, H3K4me2/3-rich promoters through its MBT repeats, SLED/SDB DNA-binding domains, and an RNA-binding region, facilitating PRC2-mediated H3K27me3 deposition that establishes bivalent chromatin at developmental and somatic gene loci; this sperm-borne H3K27me3 serves as a vehicle for paternal intergenerational epigenetic inheritance (PMID:29686098, PMID:37283086, PMID:18706910, PMID:24727478). The nucleoplasmic SCML2B isoform additionally participates in cell cycle regulation by stabilizing the CDK inhibitors p21 and p27 to inhibit CDK2 activity, and in the DNA damage response it competes with p53 for USP7 binding, modulating p53 stability in a context-dependent manner (PMID:24358021, PMID:37353627).

Mechanistic history

Synthesis pass · year-by-year structured walk · 13 steps
  1. 1999 Medium

    Identification of SCML2 as a human Polycomb group homolog on Xp22 established it as a candidate epigenetic regulator, but its function remained unknown.

    Evidence Genomic cloning and sequence analysis revealing homology to Drosophila Scm

    PMID:10331946

    Open questions at the time
    • No functional data; role inferred solely from sequence homology
    • Expression pattern not characterized beyond genomic mapping
  2. 2008 High

    Structural determination of the MBT domains revealed that SCML2 reads monomethylated histone marks via an aromatic cage in the second MBT repeat, providing the first molecular mechanism for its chromatin engagement.

    Evidence X-ray crystallography and NMR spectroscopy of MBT domain–histone peptide complexes

    PMID:18706910

    Open questions at the time
    • In vivo relevance of monomethyllysine binding not tested
    • Contribution of MBT domains relative to other targeting domains unknown
  3. 2013 High

    Discovery that the nucleoplasmic SCML2B isoform directly enhances p21/p27-mediated CDK2 inhibition revealed an unexpected cell cycle regulatory function for a Polycomb protein, linking PcG biology to G1/S checkpoint control.

    Evidence Co-IP, in vitro kinase assays, and flow cytometry in human cells

    PMID:24358021

    Open questions at the time
    • Physiological significance during spermatogenesis not addressed
    • Whether CDK-mediated phosphorylation of SCML2B feeds back to chromatin function was unclear
  4. 2014 High

    Identification of the RNA-binding region (RBR) and SLED DNA-binding domain established that SCML2A uses multivalent interactions—PRC1 binding via SPM, ncRNA binding via RBR, histone reading via MBT, and DNA binding via SLED—for chromatin targeting, explaining how it achieves locus specificity.

    Evidence ChIP-seq, RNA immunoprecipitation, domain deletion mutants in human cells; NMR structure of SLED domain with DNA-binding assays

    PMID:24727478 PMID:24986859

    Open questions at the time
    • Identities of ncRNA partners not defined
    • Whether SLED DNA binding is truly sequence-specific in vivo was untested
  5. 2015 High

    Mouse knockout studies resolved the central paradox of SCML2 function: it promotes H2AK119ub on autosomes via PRC1/RNF2 while simultaneously recruiting USP7 to deubiquitinate H2AK119ub on sex chromosomes, establishing SCML2 as a context-dependent dual regulator of ubiquitin signaling during meiosis.

    Evidence Scml2 knockout mice with genome-wide ChIP-seq, Co-IP of SCML2–USP7, immunofluorescence on spermatocyte spreads, and USP7 localization studies

    PMID:25634095 PMID:25703348

    Open questions at the time
    • How SCML2 switches between promoting and opposing H2Aub at different genomic compartments was mechanistically unresolved
    • Whether the USP7 interaction is direct or bridged by other factors in vivo
  6. 2015 High

    In somatic cancer cells, SCML2 was shown to bridge USP7 to PRC1.4 (BMI1-containing), where USP7-mediated deubiquitination stabilizes BMI1 and RING1B, extending the SCML2–USP7 axis beyond the germline to PRC1 complex homeostasis.

    Evidence Co-IP, ChIP at target genes, USP7 pharmacological inhibition, western blot in human cell lines

    PMID:25605328

    Open questions at the time
    • Relevance of PRC1 stabilization by USP7 in the germline context not tested
    • Whether SCML2-dependent USP7 recruitment is the dominant PRC1-stabilizing mechanism was unclear
  7. 2018 High

    Genome-wide profiling in knockout spermatogonia revealed that SCML2 reads DNA hypomethylation and H3K4me2/3 to direct PRC2-mediated H3K27me3, establishing bivalent chromatin domains at developmental regulators and late-spermatogenesis genes—linking SCML2 to PRC2 cooperation, not just PRC1.

    Evidence ChIP-seq for multiple histone marks in Scml2 KO mice, ATAC-seq, bisulfite sequencing

    PMID:29686098

    Open questions at the time
    • Direct physical interaction between SCML2 and PRC2 not demonstrated
    • Whether SCML2 is needed to maintain bivalency or only to establish it was unresolved
  8. 2018 High

    Genetic epistasis between SCML2 and RNF8 on sex chromosomes showed that SCML2-mediated deubiquitination opposes both RNF8-dependent and RNF8-independent H2AK119ub, and that persistent H2AK119ub blocks H3K27ac at enhancers, revealing the crosstalk between ubiquitin and acetylation during meiotic sex chromosome inactivation.

    Evidence Rnf8/Scml2 double knockout mice with ChIP-seq for H2AK119ub and H3K27ac

    PMID:29462142

    Open questions at the time
    • Whether SCML2 enzymatically deubiquitinates or solely recruits USP7 for this was unresolved
    • Downstream transcriptional consequences of altered H3K27ac at sex-linked enhancers not fully mapped
  9. 2018 High

    SCML2 was found to accumulate at pericentromeric heterochromatin where it suppresses H2AK119ub and promotes H3K27me3, and its loss causes ectopic facultative heterochromatin and CENP-V mislocalization, extending its role to centromere-proximal chromatin organization.

    Evidence Scml2 KO mice with immunofluorescence on spermatocyte spreads and ChIP-seq

    PMID:30097555

    Open questions at the time
    • Mechanism by which SCML2 is specifically recruited to PCH not defined
    • Functional consequences of CENP-V mislocalization for chromosome segregation unknown
  10. 2019 Medium

    Identification of rapidly evolving SDB DNA-binding repeats in mouse SCML2, which cooperate with the RBR and other domains to sense DNA hypomethylation, explained how SCML2 achieves specificity for unmethylated genomic targets in vivo.

    Evidence Domain deletion mutants with ChIP-seq and in vitro DNA-binding assays

    PMID:30137219

    Open questions at the time
    • SDB repeats are poorly conserved, raising questions about the human mechanism
    • Structural basis for methylation-sensitivity of SDB repeats not determined
  11. 2023 High

    SCML2-deposited sperm H3K27me3 was shown to transmit epigenetic information intergenerationally: loss of SCML2 in fathers caused dysregulated gene expression in wild-type F1 germline and preimplantation embryos, establishing SCML2 as a mediator of paternal epigenetic inheritance.

    Evidence Scml2 KO fathers with ART rescue, ChIP-seq of testicular and epididymal sperm, RNA-seq of F1 tissues

    PMID:37283086

    Open questions at the time
    • Whether the inherited effects persist beyond the F1 generation was not tested
    • Which specific SCML2-dependent H3K27me3 loci are causally responsible for F1 phenotypes is unknown
  12. 2023 Medium

    SCML2 was integrated into the DNA damage response: CHK1 phosphorylates SCML2 at Ser570 to stabilize it, and SCML2 competes with p53 for USP7 binding via the TRAF domain, providing a mechanism by which SCML2 levels modulate p53 stability in cancer cells and p21/CHK1 stability in p53-null contexts.

    Evidence Co-IP with site-directed mutagenesis, ubiquitination assays, kinase assays in human cancer cell lines

    PMID:37353627

    Open questions at the time
    • Competition model for USP7 binding tested in overexpression systems; endogenous stoichiometry not validated
    • Relevance to the germline DNA damage response not explored
  13. 2023 Medium

    The discovery that SCML2 physically interacts with the Hippo pathway effector YAP1 in an androgen-regulated manner suggested a signaling integration point, but mechanistic consequences remain poorly defined.

    Evidence Co-IP, mass spectrometry, proximity ligation assay, GST pulldown in prostate cancer cells

    PMID:37810219

    Open questions at the time
    • Downstream transcriptional targets of SCML2–YAP1 interaction not identified
    • Whether YAP1 interaction is relevant in the germline is unknown
    • Single-lab finding without independent replication

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include the structural basis for SCML2's context-dependent switching between ubiquitination promotion and removal at different genomic compartments, the direct versus indirect nature of SCML2–PRC2 cooperation, and the extent to which SCML2-mediated paternal epigenetic inheritance affects phenotypic outcomes across generations.
  • No structural model of full-length SCML2 or its complex with USP7/PRC1 exists
  • Direct SCML2–PRC2 physical interaction has not been demonstrated
  • Transgenerational persistence of SCML2-dependent epigenetic effects beyond F1 is untested

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 4 GO:0003677 DNA binding 2 GO:0060090 molecular adaptor activity 2 GO:0003723 RNA binding 1 GO:0042393 histone binding 1
Localization
GO:0005694 chromosome 3 GO:0005654 nucleoplasm 2
Pathway
R-HSA-4839726 Chromatin organization 6 R-HSA-1474165 Reproduction 5 R-HSA-1266738 Developmental Biology 2 R-HSA-1640170 Cell Cycle 1
Partners
BMI1CDK2CDKN1ACDKN1BCHEK1RNF2USP7YAP1
Complex memberships
CDK2/CYCLIN/p21/p27PRC1PRC1.4 (BMI1-containing)

Evidence

Reading pass · 15 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1999 SCML2 was identified as a novel human gene on Xp22 homologous to Drosophila Sex comb on midleg (Scm), encoding a 700 amino acid protein and a constituent of the Polycomb group (PcG) transcriptional repressor system. Genomic cloning, sequence analysis, chromosomal mapping Genomics Medium 10331946
2008 The two MBT (malignant brain tumor) repeat domains of human SCML2 preferentially bind histone peptides monomethylated at lysine residues, with the monomethyllysine binding to an aromatic-rich pocket at one end of the beta-barrel of the second MBT repeat, as determined by NMR spectroscopy and crystal structure. NMR spectroscopy, X-ray crystallography Journal of molecular biology High 18706910
2013 SCML2B (the nucleoplasmic isoform) forms a stable complex with CDK/CYCLIN/p21 and p27, enhancing the inhibitory effect of p21/p27 on CDK2 kinase activity, thereby participating in the G1/S checkpoint; in turn, CDK/CYCLIN complexes phosphorylate SCML2B, and the interaction is regulated through the cell cycle. Protein purification, Co-IP, in vitro kinase assay, cell cycle analysis by flow cytometry PLoS biology High 24358021
2014 SCML2A (chromatin-bound isoform) binds to PRC1 via its SPM domain and interacts with ncRNAs through a novel RNA-binding region (RBR); targeting of SCML2A to chromatin involves coordinated action of MBT domains, RNA binding, and PRC1 interaction. Deletion of RBR reduces occupancy at target genes and overexpression of RBR-deleted SCML2A causes defects in PRC1 recruitment. Chromatin immunoprecipitation (ChIP), RNA immunoprecipitation, domain deletion/mutagenesis, ChIP-seq eLife High 24986859
2014 A conserved domain within human SCML2, named 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 spectroscopy. Solution NMR spectroscopy, DNA-binding assay The Journal of biological chemistry High 24727478
2015 SCML2, as a germline-specific subunit of PRC1, promotes RNF2-dependent H2A ubiquitination on autosomes to repress somatic/progenitor genes, while paradoxically preventing RNF2-dependent H2A ubiquitination on sex chromosomes during meiosis, enabling unique epigenetic programming of sex chromosomes. Mouse knockout model, ChIP-seq, immunofluorescence, H2A ubiquitination assays Developmental cell High 25703348
2015 Mouse 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, demonstrating that the SCML2/USP7 complex modulates the epigenetic state of sex chromosomes during male meiosis. Mouse knockout, Co-IP, immunofluorescence on spermatocyte spreads, H2A ubiquitination assay PLoS genetics High 25634095
2015 SCML2 bridges USP7 to PRC1.4 (BMI1-containing complex), stabilizing BMI1 via USP7-mediated deubiquitination; USP7 is found at SCML2/BMI1 target genes by ChIP, and USP7 inhibition reduces H2Aub levels and destabilizes PRC1 components RING1B and BMI1. Co-IP, ChIP, USP7 inhibition, western blot Molecular and cellular biology High 25605328
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 regulators (Class I) and somatic genes silenced during late spermatogenesis (Class II). ChIP-seq in Scml2 knockout mice, ATAC-seq, bisulfite sequencing Proceedings of the National Academy of Sciences High 29686098
2018 RNF8 and SCML2 cooperate antagonistically in ubiquitin regulation on sex chromosomes during meiosis: SCML2 deubiquitinates RNF8-independent H2AK119ub, while RNF8-dependent polyubiquitination is required for establishment of H3K27 acetylation at enhancers; persistent H2AK119ub inhibits H3K27ac. Double mutant epistasis revealed that RNF8-dependent H2AK119ub is a substrate for SCML2-mediated deubiquitination. Double knockout mouse (Rnf8 and Scml2), ChIP-seq, H2A ubiquitination assays, immunofluorescence PLoS genetics High 29462142
2018 SCML2 accumulates on pericentromeric heterochromatin (PCH) in male germ cells, suppresses PRC1-mediated H2AK119ub, and promotes PRC2-mediated H3K27me3 at PCH during meiosis; loss of SCML2 in spermatids leads to ectopic facultative heterochromatin patches and mislocalization of centromere protein CENP-V from PCH. Mouse KO, immunofluorescence on spermatocyte spreads, ChIP-seq, western blot Journal of cell science High 30097555
2019 Mouse SCML2 contains a novel rapidly evolved DNA-binding domain called SDB (SCML2 DNA-binding) repeats composed of 28-amino acid repeat units; these repeats cooperate with the RNA-binding region and other domains to recruit SCML2 to hypomethylated chromatin targets, enabling sensing of DNA hypomethylation in vivo. Domain deletion/mutagenesis, ChIP-seq, in vitro DNA-binding assay, bisulfite sequencing Biology of reproduction Medium 30137219
2023 SCML2 mediates paternal epigenetic inheritance: SCML2 is required for PRC2-dependent H3K27me3 deposition in testicular sperm at bivalent promoters, and loss of SCML2 in F0 fathers dysregulates gene expression in wild-type F1 male germline and preimplantation embryos, identifying SCML2-mediated sperm H3K27me3 as a vehicle of intergenerational epigenetic information. Mouse KO with ART rescue, ChIP-seq of testicular and epididymal sperm, RNA-seq of F1 germ cells and embryos Nucleic acids research High 37283086
2023 DNA damage stabilizes SCML2 through CHK1-mediated phosphorylation at Ser570. In p53-positive cancer cells, SCML2 binds the TRAF domain of USP7 (via Ser441) and competes with p53 for USP7 binding, thereby destabilizing p53. In p53-negative cells, SCML2 promotes CHK1 and p21 stability by inhibiting their ubiquitination; SCML2A primarily stabilizes CHK1, while SCML2B regulates p21 stability. Co-IP, site-directed mutagenesis, ubiquitination assay, kinase assay, western blot, cell viability assay Cell death and differentiation Medium 37353627
2023 SCML2 physically interacts with transcriptional cofactor YAP1, as shown by co-immunoprecipitation, mass spectrometry, proximity ligation assay, and GST pulldown; androgen signaling regulates this interaction, and SCML2 knockdown alters cell growth in response to androgen. Co-IP, mass spectrometry, proximity ligation assay, GST pulldown, RNAi iScience Medium 37810219

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 114 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 67 29686098
2015 Polycomb protein SCML2 associates with USP7 and counteracts histone H2A ubiquitination in the XY chromatin during male meiosis. PLoS genetics 65 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 26 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 12 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 0 37810219