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Stem cell proliferation is kept in check by the chromatin regulators Kismet/CHD7/CHD8 and Trr/MLL3/4

ABSTRACT: Chromatin remodeling accompanies differentiation, however, its role in self-renewal is less-well understood. We report that in Drosophila the chromatin remodeler Kismet/CHD7/CHD8 limits intestinal stem cells (ISC) number and proliferation without affecting differentiation. Stem cell-specific whole-genome profiling of Kismet revealed its enrichment at transcriptionally active regions bound by RNA Polymerase II and Brahma, its recruitment to transcription start site of activated genes and developmental enhancers and its depletion from regions bound by Polycomb, Histone H1 and heterochromatin Protein 1. We demonstrate that the Trithorax-related/MLL3/4 chromatin modifier regulates ISC proliferation, colocalizes extensively with Kismet throughout ISC genome, and co-regulates genes in ISCs, including Cbl a negative regulator of Epidermal Growth Factor Receptor (EGFR). Loss of kismet or trr leads to elevated levels of EGFR protein and signaling, thereby promoting ISC self-renewal. We propose that Kismet with Trr establishes a chromatin state that limits EGFR proliferative signaling, preventing tumor-like stem cell overgrowths.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE128941 | GEO | 2019/03/28

REPOSITORIES: GEO

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Project description:Background & Aims: Hierarchical organization of intestine relies on their stem cells by self-renew and producing committed progenitors. Although signals like Wnt are known to animate the continued renewal by maintaining intestinal stem cells (ISCs) activity, molecular mechanisms especially E3 ubiquitin ligases that modulate ISCs ‘stemness’ and supportive niche have not been well understood. Here, we investigated the role of Cullin 4B (Cul4b) in regulating ISC functions. Methods: We generated mice with intestinal epithelial-specific disruption of Cul4b (pVillin-cre; Cul4bfn/Y), inducible disruption of Cul4b (Lgr5-creERT2; Cul4bfn/Y, CAG-creERT2; Cul4bfn/Y) and their control (Cul4bfn/Y). Intestinal tissues were analyzed by histology, immunofluorescence, RNA sequencing and mass spectrum. Intestinal organoids deprived from mice with pVillin-Cre; Cul4bfn/Y, Lgr5-Cre; Cul4bfn/Y, Tg-Cul4b and their controls were used in assays to measure intestinal self-renewal, proliferation and differentiation. Wnt signaling and intestinal markers were analyzed by immunofluorescence and immunoblot assays. Differential proteins upon Cul4b ablation or Cul4b-interacting proteins were identified by mass spectrometry. Results: Cul4b specifically located at ISCs zone. Block of Cul4b impaired intestinal homeostasis maintenance by reduced self-renewal and proliferation. Transcriptome analysis revealed that Cul4b-null intestine lose ISC characterization and showed disturbed ISC niche. Mechanistically, reactivated Wnt pathway could recover intestinal dysfunction of Cul4b knockout mice. Analysis of differential total and ubiquitylated proteins uncovered the novel targeting substrate of Cullin-Ring ubiquitin ligase 4b (CRL4b), immunity-related GTPase family M member 1 (Irgm1) in intestine. Decreased Irgm1 rescued abnormally interferon signaling, overemphasized autophagy and downstream phosphate proteins in Cul4b knockout mice. Conclusion: We conclude that Cul4b is essential for ISC self-renewal and Paneth cell function by targeting Irgm1 and modulating Wnt signaling. Our results demonstrate that Cul4b is a novel ISC stemness and niche regulator.

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Stem cell proliferation is kept in check by the chromatin regulators Kismet/CHD7/CHD8 and Trr/MLL3/4

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