EMBO Reports最新文献

Cell polarity is a crucial biological process essential for cell division, directed growth, and motility. In Saccharomyces cerevisiae, polarity establishment centers around the small Rho-type GTPase Cdc42, which cycles between GTP-bound and GDP-bound states, regulated by GEFs like Cdc24 and GAPs such as Rga2. To dissect the dynamic regulation of Cdc42, we employed in vitro GTPase assays, revealing inverse concentration-dependent profiles for Cdc24 and Rga2: with increasing concentration, Cdc24's GEF activity is nonlinear and oligomerization-dependent, which is possibly linked to the relief of its self-inhibition. In contrast, Rga2's GAP activity saturates, likely due to self-inhibition upon oligomerization. Together, Cdc24 and Rga2 exhibit a strong synergy driven by weak Cdc24-Rga2 binding. We propose that the synergy stems from Cdc24 alleviating the self-inhibition of oligomeric Rga2. We believe this synergy contributes to efficient regulation of Cdc42's GTPase cycle over a wide range of cycling rates, enabling cells to resourcefully establish polarity. As Cdc42 is highly conserved among eukaryotes, we propose the GEF-GAP synergy to be a general regulatory property in other eukaryotes.

Proper histone gene expression is critical for cell viability and maintenance of genomic integrity. Multiple histone genes are organized into three genomic loci that encode replication-coupled core and linker histones. Histone gene expression and transcript processing are orchestrated in the histone locus body (HLB) within the nucleus. Here, we identify human CRAMP1 as a selective regulator of the linker histone H1 expression. Human CRAMP1 is recruited to the HLB in RPE1^hTERT cells. Immunoprecipitation combined with mass spectrometry shows CRAMP1 physically associates with the HLB component GON4L (also known as YARP). We demonstrate that the PAH domains of GON4L interact with CRAMP1. CRAMP1 disruption results in reduced histone H1 mRNA expression and histone H1 protein levels, with no significant changes in core histone gene expression. CRAMP1 occupies the promoters of actively expressed replication-coupled linker histone genes that reside within the histone locus body and replication-independent histone H1 loci, which reside in a region of the genome without other histone genes. Together, these data identify CRAMP1 as a novel and selective regulator of histone H1 gene expression.

Proper regulation of ribosome biogenesis is essential for stem cell function and tissue homeostasis, yet its upstream control in adult intestinal stem cells (ISCs) remains unclear. Here, we identify the WD repeat protein Wdr4 as a key regulator of ISC homeostasis in the Drosophila midgut. Wdr4 cooperates with the methyltransferase Mettl1 to catalyze N⁷-methylguanosine (m⁷G) modification of let-7 miRNA. Wdr4 or Mettl1 depletion disrupts this modification, reducing let-7 levels and aberrantly activating TOR-JNK-dMyc signaling. This drives elevated ribosome biogenesis, ISC overproliferation, misdifferentiation, and intestinal dysplasia. Overexpression of let-7, inhibition of TOR, or suppression of JNK rescues these defects. Importantly, expression of human WDR4 and METTL1, but not catalytic-dead METTL1 mutant, restores ISC homeostasis in Wdr4- and Mettl1-depleted flies, establishing a conserved Wdr4/Mettl1-let-7-TOR-JNK axis that links miRNA modification to translational control and tissue integrity. Together, our findings uncover a previously unrecognized function of miRNA m⁷G methylation in regulating ribosome biogenesis and maintaining intestinal homeostasis.

In many animals, primordial germ cells are transiently segregated outside the somatic-cell cluster that forms the embryo's body during early embryogenesis. This physical segregation of the germline from the soma has long been believed to be crucial for germline development, but the mechanisms controlling this segregation and its developmental significance remain unclear. Here, in Drosophila, we show that somatic gene silencing in the germline is essential for maintaining this segregation. Primordial germ cells (pole cells) lacking the Nanos- and Polar granule component (Pgc)-dependent dual repression mechanism misexpress widespread somatic genes. They form abnormal cellular protrusions, invade adjacent somatic epithelium, and intermingle with somatic cells. These mislocalized pole cells ultimately undergo cell death, whereas properly segregated cells survive. Notably, knockdown of miranda (mira), one of the somatic genes ectopically expressed, rescues these phenotypes. Our findings uncover a previously unrecognized mechanism whereby somatic gene silencing safeguards the physical boundary between the germline and the somatic cells forming the embryo's body, highlighting its potential role in ensuring germline viability during early development.

The centriole duplication cycle must be tightly controlled and coordinated with the chromosome cycle. Aberrations in centriole biogenesis can cause developmental disorders, ciliopathies and cancer, yet the molecular determinants controlling centriole numbers and the link between the two cycles remain poorly characterized. Here, we demonstrate that McIdas, previously implicated in cell cycle regulation and multiciliogenesis, plays a critical role in maintaining proper centriole numbers. McIdas localizes to centrioles, where it exhibits dynamic localization throughout the cell cycle, dependent upon a nuclear export signal (NES) in its coiled-coil domain. Overexpression of McIdas induces centriole overduplication, whereas its depletion perturbs daughter centriole biogenesis and SAS6 recruitment. An NES mutant of McIdas that fails to localize to centrioles does not induce centriole amplification. Moreover, McIdas depletion reduces PLK4-induced centriole amplification. McIdas interacts with and is phosphorylated by PLK4, which is critical for its role in centriole number control. Overall, our results demonstrate that in addition to its known nuclear localization, McIdas also localizes to centrioles, affecting centriole duplication. This novel, direct role of McIdas in centriole duplication connects its functions in cell cycle regulation and multiciliogenesis.

The Drosophila Toll/NF-κB pathway has been extensively studied for its roles in innate immunity and embryonic development. Nevertheless, the regulatory mechanisms underlying Spz/Toll signaling in non-immune contexts remain poorly understood. Here, we demonstrate a critical role for Toll in regulating intestinal stem cell activity through direct transcriptional control of PI3K and Akt in an insulin-independent manner. Time-series transcriptomic analysis of intestinal damage and repair responses reveals that the stress-responsive factor Jumu regulates Spz expression to activate Toll signaling. Disruption of the Jumu/Spz/Toll cascade or PI3K/Akt signaling impairs intestinal regeneration and suppresses tumor growth, and epistasis analysis confirms that PI3K/Akt functions downstream of Toll. Our findings elucidate an autocrine Spz/Toll-mediated mechanism that drives stem cell function via the PI3K/Akt pathway during tissue homeostasis and uncover a critical non-immune role of Toll signaling in both physiological and pathological contexts.

Cyclic guanosine monophosphate (GMP)-AMP synthase (cGAS) is a critical cytosolic DNA sensor, whose activity can be regulated by acetylation. Here, we show that nicotinamide adenine dinucleotide (NAD⁺)-dependent lysine deacetylase SIRT4 interacts with cGAS and positively regulates innate immune responses triggered by DNA viruses or cytoplasmic DNA. Overexpression of SIRT4 inhibits HSV-1 infection, whereas knockdown of SIRT4 has the opposite effect. Deficiency of SIRT4, or treatment with a SIRT4 inhibitor, impairs antiviral innate immune signaling in response to DNA viruses or cytoplasmic DNA, both in vitro and in vivo. Moreover, SIRT4 inhibitor treatment attenuates type I interferon signaling in Trex1-deficient cells and in peripheral blood mononuclear cells (PBMCs) from patients with systemic lupus erythematosus (SLE). Mechanistically, SIRT4 deacetylates cGAS and enhances its association with double‑stranded DNA. Collectively, our study identifies SIRT4 as a positive regulator of cGAS-mediated innate immune signaling pathways, which advances the understanding of the regulation of cGAS activity.