title: Sex comb on midleg (Scm) is a functional link between PcG-repressive complexes in Drosophila.
abstract: The Polycomb group (PcG) proteins are key regulators of development in Drosophila and are strongly implicated in human health and disease. How PcG complexes form repressive chromatin domains remains unclear. Using cross-linked affinity purifications of BioTAP-Polycomb (Pc) or BioTAP-Enhancer of zeste [E(z)], we captured all PcG-repressive complex 1 (PRC1) or PRC2 core components and Sex comb on midleg (Scm) as the only protein strongly enriched with both complexes. Although previously not linked to PRC2, we confirmed direct binding of Scm and PRC2 using recombinant protein expression and colocalization of Scm with PRC1, PRC2, and H3K27me3 in embryos and cultured cells using ChIP-seq (chromatin immunoprecipitation [ChIP] combined with deep sequencing). Furthermore, we found that RNAi knockdown of Scm and overexpression of the dominant-negative Scm-SAM (sterile α motif) domain both affected the binding pattern of E(z) on polytene chromosomes. Aberrant localization of the Scm-SAM domain in long contiguous regions on polytene chromosomes revealed its independent ability to spread on chromatin, consistent with its previously described ability to oligomerize in vitro. Pull-downs of BioTAP-Scm captured PRC1 and PRC2 and additional repressive complexes, including PhoRC, LINT, and CtBP. We propose that Scm is a key mediator connecting PRC1, PRC2, and transcriptional silencing. Combined with previous structural and genetic analyses, our results strongly suggest that Scm coordinates PcG complexes and polymerizes to produce broad domains of PcG silencing.
authors.affiliation: Division of Genetics, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA; Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA;
authors.forename: Hyuckjoon
authors.initials: H
authors.lastname: Kang
authors.affiliation: Division of Genetics, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA; Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA; Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA;
authors.forename: Kyle A
authors.initials: KA
authors.lastname: McElroy
authors.affiliation: Division of Genetics, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA; Center for Biomedical Informatics, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: Youngsook Lucy
authors.initials: YL
authors.lastname: Jung
authors.affiliation: Division of Genetics, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA; Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA;
authors.forename: Artyom A
authors.initials: AA
authors.lastname: Alekseyenko
authors.affiliation: Division of Genetics, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA; Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA;
authors.forename: Barry M
authors.initials: BM
authors.lastname: Zee
authors.affiliation: Division of Genetics, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA; Center for Biomedical Informatics, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Park
authors.affiliation: Division of Genetics, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA; Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA; mkuroda@genetics.med.harvard.edu.
authors.forename: Mitzi I
authors.initials: MI
authors.lastname: Kuroda
mesh_terms: D000818:Animals; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D063146:Polycomb-Group Proteins / Q000235:genetics / Q000378:metabolism*; D059007:Polytene Chromosomes / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D012097:Repressor Proteins / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D006657:Histones; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins; C099357:SCM protein, Drosophila
keywords: BioTAP-XL; Drosophila; Polycomb group (PcG); SAM domain; Scm