Biology subjects

Ivens, A.

Publications and source records attributed to Ivens, A..

8 recordsLinked to original sources

bioRxiv2026

A Genome-Wide Genetic Screen Identifies a Novel kDNA Replication Protein in Trypanosomes

Mitochondrial DNA of trypanosomatid parasites is organized into a topologically complex structure, named kinetoplast (kDNA). Replication, segregation and expression of kDNA involve an estimated [~]300 proteins, only a fraction of which have been identified and characterized. Here, we report the development of a genetic screen in Trypanosoma brucei to identify novel kDNA maintenance factors. Of the 20 highest-ranked genes identified, six are known kDNA maintenance factors. We selected one hit, Tb927.8.4240, a gene of previously unknown function, for experimental follow-up. Ultrastructure expansion microscopy using a tagged version of the protein reveals a dynamic localization during the cell cycle. RNAi-mediated ablation of Tb927.8.4240 results in the progressive but incomplete loss of kDNA, with only a minor effect on the tripartite attachment complex, suggesting the protein is involved in kDNA replication but not segregation. The growth phenotype of Tb927.8.4240 ablation is fully rescued in a kDNA-independent genetic background, confirming a specific role in kDNA replication. In summary, we describe a functional genetic screen for the identification of kDNA maintenance factors in trypanosomes, validate one hit as a novel kDNA replication factor, and provide a prioritized hit list as a promising starting point for the future identification of additional factors.

molecular biology↗

bioRxiv2025

Control of retrotransposon-driven activation of the interferon response by the double-stranded RNA binding protein DGCR8

The type I interferon (IFN) response is the main innate immune pathway against viruses in mammals. This pathway must be tightly regulated to prevent viral spread while avoiding excessive immune responses. Here, we show that inactivation of the double-stranded RNA (dsRNA)-binding protein DGCR8 unleashes the IFN response in human cells. We demonstrate that DGCR8 restricts the accumulation of endogenous dsRNA originating from protein-coding mRNAs that harbour transposable elements (TEs), primarily Alu. We propose that DGCR8 binding to TE-rich mRNAs is essential to resolve dsRNA structures, and in its absence, accumulated dsRNA signals through the RIG-I-like signalling pathway triggering the IFN response. This mechanism is relevant to conditions where DGCR8 expression levels are altered, including the 22q11.2 deletion syndrome (22qDS). Supporting this, we show that 22qDS-derived cells exhibit an exacerbated type I IFN response which inversely correlated with DGCR8 levels. All these together demonstrate the importance of suppressing endogenous TE-dsRNA accumulation to prevent unwanted immune activation and associated disease pathogenesis.

molecular biology↗

bioRxiv2025

Double stranded RNA sensing drives interferon silencing in early development

In early mammalian development, the type I interferon (IFN) response is inactive, only becoming functional after gastrulation. As a result, the totipotent and pluripotent embryonic stages remain highly susceptible to pathogens, including viruses. Here, we show that pluripotent mouse embryonic stem cells (mESCs) suppress the RIG-I-like receptor sensing pathway by silencing the expression of the dsRNA sensor MDA5. We show that this silencing is required to avoid the recognition of dsRNAs from endogenous origin, which only accumulate in mESCs. Reintroducing MDA5 results in recognition of these endogenous dsRNAs, and activation of the IFN response through IRF3. The production of IFN alters the differentiation ability of mESCs, as well as the pluripotency gene expression program, as shown by epigenetic, transcriptomic and proteomic analyses. These findings are conserved in zebrafish, where MDA5 is also expressed at later stages of development. Similarly, zebrafish lack early-stage IFN activation and premature IFN signalling results in developmental defects. Altogether, we conclude that silencing the RIG-I-like receptor pathway during early development is the widely conserved and is required to prevent aberrant immune recognition of endogenous dsRNAs, safeguarding normal development.

cell biology↗

bioRxiv2024

Developmental editing control of mRNA ND7 involves KREH2 helicase-dependent gRNAselection and proposed RNA structure in Trypanosoma brucei

Unknown factors regulate mitochondrial U-insertion/deletion (U-indel) RNA editing in procyclic-form (PCF) and bloodstream-form (BSF) T. brucei. This editing, directed by anti-sense gRNAs, creates canonical protein-encoding mRNAs and may developmentally control respiration. Canonical editing by gRNAs that specify protein-encoding mRNA sequences occurs amid massive non-canonical editing of unclear sources and biological significance. We found PCF-specific repression at a major early checkpoint in mRNA ND7, involving helicase KREH2-dependent opposite modulation of canonical and non-canonical "terminator" gRNA utilization. Terminator-programmed editing derails canonical editing and installs proposed repressive structure in 30% of the ND7 transcriptome. BSF-to-PCF differentiation in vitro recreated this negative control. Remarkably, KREH2-RNAi knockdown relieved repression and increased editing progression by reverting canonical/terminator gRNA utilization. ND7 transcripts lacking early terminator-directed editing in PCF exhibited similar negative editing control along the mRNA sequence, suggesting global modulation of gRNA utilization fidelity. The terminator is a "moonlighting" gRNA also associated with mRNA COX3 canonical editing, so the gRNA transcriptome seems multifunctional. Thus, KREH2 is the first identified repressor in developmental editing control. This and our prior work support a model whereby KREH2 activates or represses editing in a stage and substrate-specific manner. KREH2s novel dual role tunes mitochondrial gene expression in either direction during development.

molecular biology↗

bioRxiv2024

DGCR8 haploinsufficiency leads to primate-specific RNA dysregulation and pluripotency defects

The 22q11.2 deletion syndrome (22qDS) is caused by a microdeletion in chromosome 22, including DGCR8, an essential gene for miRNA production. The contribution of human DGCR8 hemizygosity to the disease is still unclear. In this study, we generated two human pluripotent cell models containing a single functional DGCR8 allele to elucidate its role on 22qDS. DGCR8+/-cells show increased apoptosis as well as self-renewal and differentiation defects in both the naive and primed states. The expression of primate-specific miRNAs was largely affected, due to impaired miRNA processing and chromatin accessibility. DGCR8+/- cells also displayed a pronounced reduction in human endogenous retrovirus class H (HERVH) expression, a primate-specific retroelement essential for pluripotency maintenance. Importantly, the reintroduction of primate-specific miRNAs as well as the miR-371-3 cluster rescued the cellular and molecular phenotypes of DGCR8+/-cells. Our results suggest that DGCR8 is haploinsufficient in humans and that miRNAs and transposable elements may have co-evolved in primates as part of an essential regulatory network to maintain stem cell identity.

molecular biology↗

bioRxiv2023

A conserved trypanosomatid differentiation regulator controls substrate attachment and morphological development in Trypanosoma congolense

Trypanosomatid parasites undergo developmental regulation to adapt to the different environments encountered during their life cycle. In Trypanosoma brucei, a genome wide selectional screen previously identified a regulator of the protein family ESAG9, which is highly expressed in stumpy forms, a morphologically distinct bloodstream stage adapted for tsetse transmission. This regulator, TbREG9.1, has an orthologue in Trypanosoma congolense, despite the absence of a stumpy morphotype in that parasite species, which is an important cause of livestock trypanosomosis. RNAi mediated gene silencing of TcREG9.1 in Trypanosoma congolense caused a loss of attachment of the parasites to a surface substrate in vitro, a key feature of the biology of these parasites that is distinct from T. brucei. This detachment was phenocopied by treatment of the parasites with a phosphodiesterase inhibitor, which also promotes detachment in the insect trypanosomatid Crithidia fasciculata. RNAseq analysis revealed that TcREG9.1 silencing caused the upregulation of mRNAs for several classes of surface molecules, including transferrin receptor-like molecules, immunodominant proteins, and molecules related to those associated with stumpy development in T. brucei. Depletion of TcREG9.1 in vivo also generated an enhanced level of parasites in the blood circulation consistent with reduced parasite attachment to the microvasculature. The morphological progression to insect forms of the parasite was also perturbed. We propose a model whereby TcREG9.1 acts as a regulator of attachment and development, with detached parasites being adapted for transmission. Author summaryTrypanosoma congolense is a major cause of livestock trypanosomosis in sub-Saharan Africa where it contributes to lost economic productivity and poverty. These parasites differ in two key respects from the better-studied African trypanosomes, Trypanosoma brucei. Firstly, T. congolense adheres to surfaces in vitro and in the vaculature in vivo. Secondly, they lack a morphologically distinct transmission stage equivalent to the stumpy form of T. brucei. In the current work we identify a T congolense orthologue of a key developmental regulator in T. brucei, REG9.1, previously identified by a genome-wide RNAi screen. By RNA interference in transgenic T. congolense we demonstrate that TcREG9.1 functions both in parasite adherence in vitro and in vivo, and also in parasite development. The work provides a first insight into the unusual adherence and developmental biology of T. congolense and also suggests a possible model for how these characteristics interact to promote disease spread.

microbiology↗

bioRxiv2020

Inducible mechanisms of disease tolerance provide an alternative strategy of acquired immunity to malaria

Immunity to malaria is often considered slow to develop but this only applies to defense mechanisms that function to eliminate parasites (resistance). In contrast, immunity to severe disease can be acquired quickly and without the need for improved pathogen control (tolerance). We show that a single malaria episode is sufficient to induce host adaptations that can minimise inflammation, prevent tissue damage and avert endothelium activation, a hallmark of severe disease. Furthermore, monocytes are functionally reprogrammed in tolerised hosts to prevent their differentiation into inflammatory macrophages and instead promote mechanisms of stress tolerance to protect their niche. This alternative fate is not underpinned by epigenetic reprogramming of bone marrow progenitors but is imprinted within the remodelled spleen. Crucially, all of these adaptations operate independently of pathogen load and limit the damage caused by malaria parasites in subsequent infections. Inducible mechanisms of disease tolerance therefore provide an alternative strategy of acquired immunity.

immunology↗

bioRxiv2019

Identification of a functional small non-coding RNA encoded by African swine fever virus

African swine fever virus (ASFV) causes a lethal haemorrhagic disease of domestic pigs, to which there is no vaccine available. ASFV has a large, double-stranded DNA genome that encodes over 150 proteins. Replication takes place in the cytoplasm of the cell and involves complex interactions with host cellular components including small non-coding RNAs (sncRNAs). A number of DNA viruses are known to manipulate sncRNA either by encoding their own or disrupting host sncRNA. In order to investigate the interplay between ASFV and sncRNAs, study of host and viral small RNAs extracted from ASFV-infected primary porcine macrophages (PAMs) was undertaken. We discovered that ASFV infection had only a modest effect on host miRNAs, with only 6 miRNAs differentially expressed during infection. The data also revealed 3 potential novel small RNAs encoded by ASFV, ASFVsRNA1-3. Further investigation of ASFVsRNA2 detected it in lymphoid tissue from pigs with ASF. Overexpression of ASFVsRNA2 led to up to a 1 log reduction in ASFV growth indicating that ASFV utilises a virally-encoded small RNA to disrupt its own replication. This study describes the modest impact of ASFV on host sncRNAs and the identification of a functional ASFV-encoded sncRNA. ImportanceAfrican swine fever (ASF) poses a major threat to pig populations and food security worldwide. The disease is endemic in Africa and Eastern Europe and rapidly emerging into Asia where it has led to the deaths of millions of pigs in the past 12 months. The development of safe and effective vaccines to protect pigs against ASF has been hindered by lack of understanding of the complex interactions between ASFV and the host cell. We focused our work on characterising the interactions between ASFV and sncRNAs. We found only modest changes to host sncRNA abundance after ASFV infection, and discovered a functional ASFV-encoded sncRNA. The knowledge from this study can be exploited to develop more effective ASFV vaccines that take advantage of the sncRNA system.

molecular biology↗