Biology subjects

Appert, A.

Publications and source records attributed to Appert, A..

9 recordsLinked to original sources

bioRxiv2026

Innate immune stress pathway activation underlies heterochromatin dysfunction pathology

Heterochromatin loss disrupts nuclear architecture, gene regulation and repetitive element silencing, and is associated with diverse human diseases. However, mechanisms linking heterochromatin dysfunction to pathological phenotypes remain unclear. Using genetic interaction screening and genomic analyses in C. elegans, we identify secondary activation of the Intracellular Pathogen Response (IPR), an innate immune stress pathway, as a major contributor to heterochromatin mutant phenotypes. Constitutive IPR activation phenocopies slow growth and indirect transcriptional changes observed in these mutants. Depletion of genetic enhancers further increased, whereas suppressor RNAi attenuated IPR activation, with direct heterochromatin targets remaining substantially deregulated. Notably, many suppressors encode active chromatin components, and mild reduction of RNA polymerase II activity ameliorates growth defects in C. elegans HP1 mutants and human HP1-deficient cells. Our findings reveal secondary stress response activation as an important mechanism linking heterochromatin dysfunction to pathology and identify transcriptional dampening as a potential therapeutic strategy for mitigating these effects.

genetics↗

bioRxiv2026

The SynMuvA lin-15A licenses natural transdifferentiation by antagonizing identity safeguarding mechanisms

The mechanisms that restrict or enable latent cellular plasticity have attracted growing interest over the past decade, with important implications for cancer and regenerative therapies. However, the diversity of both pro- and anti-plasticity mechanisms remains incompletely understood. Here, we identify the THAP domain gene lin-15A as a novel factor involved in the natural rectal-to-neuronal Y-to-PDA transdifferentiation in Caenorhabditis elegans. We found that, unlike previously described essential factors, lin-15A is not a Driver of transdifferentiation. Instead, it antagonizes several chromatin-modifying complexes known to safeguard differentiated cell identities. We also show that lin-15A is not a core plasticity factor per se but acts as one specifically in the Y cell context. Together, our findings support a model in which diverse molecular players coordinate controlled cell identity conversions: plasticity factors function as Drivers, while others like lin-15A which we propose to term Licensers attenuate identity safeguarding mechanisms, thereby facilitating transdifferentiation.

developmental biology↗

bioRxiv2024

A lineage-resolved multimodal single-cell atlas reveals the genomic dynamics of early C. elegans development

Multimodal single-cell profiling provides a powerful approach for unravelling the gene regulatory mechanisms that drive development, by simultaneously capturing cell-type- specific transcriptional and chromatin states. However, its inherently destructive nature hampers the ability to trace regulatory dynamics between mother and daughter cells. Taking advantage of the invariant cell lineage of Caenorhabditis elegans, we constructed a lineage- resolved single-cell multimodal map of pre-gastrulation development, which allows the tracing of chromatin and gene expression changes across cell divisions and regulatory cascades. We characterise the early dynamics of genome regulation, revealing that zygotic genome activation occurs on an accessible chromatin landscape pre-patterned both maternally and zygotically, and we identify a redundant family of transcriptional regulators that drive a transient pre-gastrulation program. Our findings demonstrate the power of a lineage-resolved atlas for dissecting the genome regulatory events of development.

genomics↗

bioRxiv2023

The histone chaperone activity of SPT2 controls chromatin structure and function in Metazoa

Histone chaperones control nucleosome density and chromatin structure. In yeast, the H3-H4 chaperone Spt2 controls histone deposition at active genes but its roles in metazoan chromatin structure and organismal physiology are not known. Here we identify the Caenorhabditis elegans orthologue of SPT2 (CeSPT-2) and show that its ability to bind histones H3-H4 is important for germline development and transgenerational epigenetic gene silencing, and that spt-2 mutants display signatures of a global stress response. Genome-wide profiling showed that CeSPT-2 binds to a range of highly expressed genes, and we find that spt-2 mutants have increased chromatin accessibility at these loci. We also show that human SPT2 controls the incorporation of new H3.3 into chromatin. Our work reveals roles for SPT2 in controlling chromatin structure and function in Metazoa.

molecular biology↗

bioRxiv2022

Widespread transposon co-option in the Caenorhabditis germline regulatory network

The movement of selfish DNA elements can lead to widespread genomic alterations with potential to create novel functions. Here we show that transposon expansions in Caenorhabditis nematodes led to extensive rewiring of germline transcriptional regulation. We find that about one third of C. elegans germline-specific promoters have been co-opted from two related Miniature Inverted Repeat Transposable Elements (MITEs), CERP2 and CELE2. The promoters are regulated by HIM-17, a THAP domain-containing transcription factor related to a transposase. Expansion of CERP2 occurred prior to radiation of the Caenorhabditis genus, as did fixation of mutations in HIM-17 through positive selection, whereas CELE2 expanded only in C. elegans. Through comparative analyses in C. briggsae, we find evolutionary conservation of most CERP2 co-opted promoters, but a substantial fraction of events are species specific. Our work reveals the emergence of a novel transcriptional network driven by TE co-option with a major impact on regulatory evolution.

genomics↗

bioRxiv2020

DREAM represses distinct targets by cooperating with different THAP domain proteins

The DREAM (DP, Retinoblastoma [Rb]-like, E2F, and MuvB) complex controls cellular quiescence by repressing cell cycle and other genes, but its mechanism of action is unclear. Here we demonstrate that two C. elegans THAP domain proteins, LIN-15B and LIN-36, co-localize with DREAM and function by different mechanisms for repression of distinct sets of targets. LIN-36 represses classical cell cycle targets by promoting DREAM binding and gene body enrichment of H2A.Z, and we find that DREAM subunit EFL-1/E2F is specific for LIN-36 targets. In contrast, LIN-15B represses germline specific targets in the soma by facilitating H3K9me2 promoter marking. We further find that LIN-36 and LIN-15B differently regulate DREAM binding. In humans, THAP proteins have been implicated in cell cycle regulation by poorly understood mechanisms. We propose that THAP domain proteins are key mediators of Rb/DREAM function.

genomics↗

bioRxiv2018

Physical and functional interaction between SET1/COMPASS complex component CFP-1 and a Sin3 HDAC complex

The CFP1 CXXC zinc finger protein targets the SET1/COMPASS complex to non-methylated CpG rich promoters to implement tri-methylation of histone H3 Ly4 (H3K4me3). Although H3K4me3 is widely associated with gene expression, the effects of CFP1 loss depend on chromatin context, so it is important to understand the relationship between CFP1 and other chromatin factors. Using a proteomics approach, we identified an unexpected link between C. elegans CFP-1 and a Rpd3/Sin3 histone deacetylase complex. We find that mutants of CFP-1, SIN-3, and the catalytic subunit SET-2/SET1 have similar phenotypes and misregulate common genes. CFP-1 directly binds SIN-3 through a region including the conserved PAH1 domain and recruits SIN-3 and the HDA-1/HDAC subunit to H3K4me3 enriched promoters. Our results reveal a novel role for CFP-1 in mediating interaction between SET1/COMPASS and a Sin3 HDAC complex at promoters and uncover coordinate regulation of gene expression by chromatin complexes having distinct activities.

genomics↗

bioRxiv2018

Chromatin accessibility dynamics across C. elegans development and ageing

An essential step for understanding the transcriptional circuits that control development and physiology is the global identification and characterization of regulatory elements. Here we present the first map of regulatory elements across the development and ageing of an animal, identifying 42,245 elements accessible in at least one C. elegans stage. Based on nuclear transcription profiles, we define 15,714 protein-coding promoters and 19,231 putative enhancers, and find that both types of element can drive orientation-independent transcription. Additionally, hundreds of promoters produce transcripts antisense to protein coding genes, suggesting involvement in a widespread regulatory mechanism. We find that the accessibility of most elements is regulated during development and/or ageing and that patterns of accessibility change are linked to specific developmental or physiological processes. The map and characterization of regulatory elements across C. elegans life provides a platform for understanding how transcription controls development and ageing.

genomics↗

bioRxiv2017

A team of heterochromatin factors collaborates with small RNA pathways to combat repetitive elements and germline stress

Repetitive sequences derived from transposons make up a large fraction of eukaryotic genomes and must be silenced to protect genome integrity. Repetitive elements are often found in heterochromatin; however, the roles and interactions of heterochromatin proteins in repeat regulation are poorly understood. Here we show that a diverse set of C. elegans heterochromatin proteins act together with the piRNA and nuclear RNAi pathways to silence repetitive elements and prevent genotoxic stress in the germ line. Mutants in genes encoding HPL-2/HP1, LIN-13, LIN-61, LET-418/Mi-2, and H3K9me2 histone methyltransferase MET-2/SETDB1 also show functionally redundant sterility, increased germline apoptosis, DNA repair defects, and interactions with small RNA pathways. Remarkably, fertility of heterochromatin mutants could be partially restored by inhibiting cep-1/p53, endogenous meiotic double strand breaks, or the expression of MIRAGE1 DNA transposons. Functional redundancy among these factors and pathways underlies the importance of safeguarding the genome through multiple means.

genomics↗