CAF-1 promotes Notch signaling through epigenetic control of target gene expression during Drosophila development

Abstract

SUMMARYThe histone chaperone CAF-1 is known for its role in DNA replication-coupled histone deposition. However, loss of function causes lethality only in higher multicellular organisms such as mice and flies, but not in unicellular organisms such as yeasts, suggesting that CAF-1 has other important functions than histone deposition during animal development. Emerging evidence indicates that CAF-1 also has a role in higher order chromatin organization and heterochromatin-mediated gene expression; it remains unclear whether CAF-1 has a role in specific signaling cascades to promote gene expression during development. Here, we report that knockdown of one of the subunits of Drosophila CAF-1, dCAF-1-p105 (Caf1-105), results in phenotypes that resemble those of, and are augmented synergistically by, mutations of Notch positive regulatory pathway components. Depletion of dCAF-1-p105 leads to abrogation of cut expression and to downregulation of other Notch target genes in wing imaginal discs. dCAF-1-p105 is associated with Suppressor of Hairless [Su(H)] and regulates its binding to the enhancer region of E(spl)mβ. The association of dCAF-1-p105 with Su(H) on chromatin establishes an active local chromatin status for transcription by maintaining a high level of histone H4 acetylation. In response to induced Notch activation, dCAF-1 associates with the Notch intracellular domain to activate the expression of Notch target genes in cultured S2 cells, manifesting the role of dCAF-1 in Notch signaling. Together, our results reveal a novel epigenetic function of dCAF-1 in promoting Notch pathway activity that regulates normal Drosophila development.

E(y)1/TAF9 mediates the transcriptional output of Notch signaling in Drosophila

“…The regulation of this pathway occurs at different levels and is especially well-characterized for the stages before nuclear entry of NICD (Andersson et al, 2011;Guruharsha et al, 2012;Tien et al, 2009). Recent findings from our laboratory and others have shown that Notch signaling can be regulated epigenetically by the CAF1 chromatin chaperone complex or by the SWI/SNF chromatin remodeling complex in different tissues (Yu et al, 2013;Zeng et al, 2013). Our studies address how the Su(H)-NICD-Mam transcriptional complex of the Notch pathway interacts with the general transcription factor complexes to initiate expression of Notch target genes.…”

“…These genetic experiments suggest that e(y)1 functionally interacts with the Notch pathway during Drosophila wing development. The Notch signaling pathway is delicately regulated at multiple levels, including ligand and receptor post-translational modification, endocytosis and vesicle trafficking, and epigenetic regulation of target gene expression (Fischer et al, 2006;Fortini and Bilder, 2009;Tien et al, 2009;Yu et al, 2013;Zeng et al, 2013). Interaction between Notch ligand and receptor induces two consecutive proteolytic cleavages of the Notch receptor, S2 and S3, which results in the release of NICD (Guruharsha et al, 2012).…”

“…Although numerous Notch target genes have been identified in different tissues or organs during different developmental stages, how the Su(H)-NICD-Mam ternary complex regulates their expression is largely unclear. Recent findings in different systems have suggested that chromatin-associated epigeneticallyregulatory mechanisms are very important for proper expression of Notch target genes (Bray et al, 2005;Domanitskaya and Schüpbach, 2012;Endo et al, 2011;Kugler and Nagel, 2007;Mulligan et al, 2011;Yu et al, 2013;Zeng et al, 2013). In flies, histone chaperones Asf1 and Nap1 are differentially associated with LID-associated factor (LAF) and RPD3-LID-associated factor (RLAF) silencing complexes to mediate epigenetic silencing at the Notch target Enhancer of Split [E(spl)] cluster (Moshkin et al, 2009).…”

“…A SIRT1-LSD1 co-repressor complex regulates Notch target gene expression in both mammalian and Drosophila cultured cells (Mulligan et al, 2011). Our very recent study has demonstrated that the histone chaperone CAF-1 complex epigenetically and positively regulates Notch target gene expression in Drosophila (Yu et al, 2013). But the most basic questions of how the Su(H)-NICD-Mam complex activates expression of Notch target genes and which cofactor(s) bring it to the general transcription machinery are unanswered.…”

“…To determine whether E(y)1 is necessary for the transcription of Notch target genes when Notch signaling is artificially induced, we employed a well-documented transient Notch activation system in cultured S2 cells by transfecting a Notchexpressing plasmid, pMT-Notch (Krejcí and Bray, 2007;Yu et al, 2013). In this assay, the overexpressed full-length Notch can be cleaved to produce a constitutively active form of NICD (denoted by N ICD ) upon treatment with EDTA.…”