Biology subjects

Rosspopoff, O.

Publications and source records attributed to Rosspopoff, O..

8 recordsLinked to original sources

bioRxiv2025

Tissue-specific restriction of TE-derived regulatory elements safeguards cell-type identity

Transposable elements (TEs) have extensively reshaped the cis-regulatory landscape of mammalian genomes, yet the mechanisms that govern their context-specific activity remain incompletely understood. KRAB zinc finger proteins (KZFPs), a large family of transcription factors specialized in TE recognition, are known repressors of TE-derived regulatory activity through TRIM28-mediated H3K9me3 deposition. Here, we expand this paradigm by uncovering noncanonical relationships between TEs and KZFPs. By generating a comprehensive epigenomic map of KZFP-bound TEs, we find that the regulatory activity of ancient mammalian L2/MIR elements is broadly delineated by KZFP binding patterns, despite low H3K9me3 enrichment. We further dissect this relationship by investigating the function of ZNF436, a non-canonical KZFP, highly expressed during in vivo human fetal heart development. Using loss-of-function approaches, we show that ZNF436 preserves cardiomyocyte function by promoting cardiac gene expression while restricting the activation of alternative lineage programs. Mechanistically, ZNF436 recruits specialized SWI/SNF chromatin remodeling complexes to limit the accessibility of L2/MIR-derived enhancers, many of which are active in non-cardiac tissues. These findings reveal a noncanonical, TRIM28-independent role for KZFPs in shaping cell-type-specific regulatory landscapes and emphasize the importance of repressing alternative regulatory programs alongside activating lineage-specific ones to safeguard cell identity.

genomics↗

bioRxiv2025

Cancer cells subvert the primate-specific KRAB zinc finger protein ZNF93 to control APOBEC3B

ZNF93 is a primate-restricted KRAB zinc finger protein responsible for repressing 20- to 12-million-year-old L1 transposable elements. Here, we reveal that ZNF93 also regulates the key cancer driver APOBEC3B--a mutagenic enzyme linked to tumorigenesis and cancer progression. ZNF93 depletion impairs DNA synthesis, activates replication and DNA damage checkpoints, and triggers proinflammatory phenotypes. Conversely, its overexpression enhances resistance to exogenous genotoxic stress, mirroring the effects observed with APOBEC3B depletion. ZNF93 expression correlates with cell proliferation rates and is overexpressed in many cancer types. These findings suggest that ZNF93 serves as a critical guardian of genome integrity, co-opted by cancer cells to counterbalance APOBEC3B-induced and L1-derived genomic instability and inflammation.

genetics↗

bioRxiv2024

Evolutionarily recent transcription factors partake in human cell cycle regulation

The cell cycle is a fundamental process in eukaryotic biology and is accordingly controlled by a highly conserved core signaling cascade. However, whether recently evolved proteins also influence this process is unclear. Here, we systematically map the influence of evolutionarily recent transcription factors (TFs) on human cell cycle progression. We find that the genomic targets of select young TFs, many of which belong to the rapidly evolving Kruppel-associated box (KRAB) zinc-finger proteins (KZFP) family, exhibit synchronized cell cycle expression. Systematic perturbation studies reveal that silencing recent TFs disrupts normal cell cycle progression, which we experimentally confirm for ZNF519, a simian-restricted KZFP. Further, we show that the therian-specific KZFP ZNF274 sets the cell cycle expression and replication timing of hundreds of clustered genes. These findings highlight an underappreciated level of lineage specificity in cell cycle regulation.

cell biology↗

bioRxiv2024

Clusters of lineage-specific genes are anchored by ZNF274 in repressive perinucleolar compartments

Long known as the site of ribosome biogenesis, the nucleolus is increasingly recognized for its role in shaping 3D genome organization. Still, the mechanisms governing the targeting of selected regions of the genome to nucleolus-associated domains (NADs) remain enigmatic. Here we reveal the essential role of ZNF274, a SCAN-bearing member of the Kruppel-associated box (KRAB)-containing zinc finger proteins (KZFP) family, in sequestering lineage-specific gene clusters within NADs. Ablation of ZNF274 triggers transcriptional activation across entire genomic neighborhoods - encompassing, among others, protocadherin and KZFP-encoding genes - with loss of repressive chromatin marks, altered 3D genome architecture and de novo CTCF binding. Mechanistically, ZNF274 anchors target DNA sequences at the nucleolus and facilitates their compartmentalization via a previously uncharted function of the SCAN domain. Our findings illuminate the mechanisms underlying NADs organization and suggest that perinucleolar entrapment into repressive hubs constrains the activation of tandemly arrayed genes to enable selective expression and modulate cell differentiation programs during development.

molecular biology↗

bioRxiv2023

Clock driven waves of Tbx6 expression prefigure somite boundaries

The segmented body plan of vertebrates is established during embryogenesis by periodic and sequential formation of multi-cellular structures called somites. Somitogenesis is an example of patterning by a biological oscillator, the segmentation clock, which manifests as traveling waves of oscillating Hes/Her gene expression, reiterating during the formation of each1-3. How these waves are converted into the striped Mesp gene expression pattern that prefigures morphological somite boundaries4-8 remains unclear. Here, we image this conversion in real-time at single-cell resolution in zebrafish, using light-sheet microscopy of a novel reporter of Tbx6, a key activator of Mesp expression. We observe cellular oscillations and kinematic waves of Tbx6 expression that are driven by Hes/Her genes. Tbx6 waves arrest precisely in boundary cells that eventually express Mesp, thereby prefiguring the Mesp pattern, whereas Hes/Her waves do not. Although Hes/Her oscillations began before somitogenesis9-11, the first Tbx6 wave defines the boundary cells of the anterior-most somite, forming the head-trunk interface. Our findings imply that Tbx6 acts as a genetic clutch, converting Her/Hes pacemaker waves into Mesp stripes. We propose that this clock design shields the pacemaker from external perturbations, allowing flexible and robust patterning, making it of interest for organoids and tissue-engineering.

developmental biology↗

bioRxiv2023

KRAB zinc finger proteins ZNF587/ZNF417 protect lymphoma cells from replicative stress-induced inflammation

Heterochromatin loss and genetic instability enhance cancer progression by favoring clonal diversity, yet uncontrolled replicative stress can lead to mitotic catastrophe and inflammatory responses promoting immune rejection. KRAB-containing zinc finger proteins (KZFPs) are epigenetic modulators, which for many control heterochromatin at transposable element (TE)-embedded regulatory sequences. We identified a cluster of 18 KZFPs associated with poor prognosis in diffuse large B cell lymphoma (DLBCL). We found their upregulation to correlate with increased copy number alterations and suppression of immune responses in tumor samples. Upon depleting two that target evolutionarily recent TEs, the primate-specific ZNF587 and ZNF417 paralogs, the proliferation of DLBCL cell lines was drastically impaired and replicative stress abruptly induced with marked alterations of the chromatin landscape and multiplication of DNA replication origins. Furthermore, ZNF587/417 knockdown upregulated interferon/inflammatory-related genes through activation of the cGAS-STING DNA sensing pathway, augmented the susceptibility of tumor cells to macrophage-mediated phagocytosis, and modified their immunogenicity through an increased surface expression of HLA-I and reshuffling of their immunopeptidome. ZNF587 and ZNF417 are thus pro-oncogenic factors allowing for higher degrees of genetic instability through attenuation of replicative stress and secondary inflammation, an influence that likely facilitates the clonal expansion, diversification, and immune evasion of cancer cells.

cancer biology↗

bioRxiv2019

A primate-specific retroviral enhancer wires the XACT lncRNA into the core pluripotency network in human

Transposable elements (TEs) have been of paramount importance in shaping genomic and epigenomic landscapes of their hosts and in driving the expansion of gene regulatory networks during mammalian evolution. They are found in nearly all long non-coding RNAs (lncRNAs) and have promoted their evolution and function, often in a species- and tissue-specific manner. X-chromosome inactivation (XCI) is an essential process that relies on several TE-enriched lncRNAs. While XCI is conserved across species, one striking difference between human and mouse is the existence of XACT (X active coating transcript), a human-specific lncRNA that coats active X chromosomes in pluripotent cells and may oppose X chromosome silencing in this context. Here, we explore how different families of TEs have contributed to shaping the XACT locus and how they couple its expression to pluripotency in humans. Through a combination of sequence analysis across primates, transcriptional interference and genome editing in human embryonic stem cells (hESCs), we identify a critical enhancer for the transcriptional regulation of the XACT locus that evolved from an ancestral group (LTR48B/ERV1) of mammalian endogenous retroviruses (ERVs), prior to the emergence of XACT. Furthermore, we show that this ancient ERV was hijacked by evolutionarily younger hominoid-specific ERVs that gave rise to the promoter of XACT, thus wiring its expression to the pluripotency network. This work illustrates how retroviral-derived sequences may intervene in species-specific regulatory pathways.

molecular biology↗

bioRxiv2019

Mechanistic diversification of XIST regulatory network in mammals

X chromosome inactivation (XCI) is a developmental regulatory process that initiates with remarkable diversity in various mammalian species. Here we addressed the contribution of XCI regulators, most of which are lncRNA genes characterized in the mouse, to this mechanistic diversity. By combining analysis of single-cell RNA-seq data from early human embryogenesis with various functional assays in naive and primed pluripotent stem cells and in differentiated cells, we demonstrate that JPX is a major regulator of XIST expression in human and in mouse. However, the underlying mechanisms differ radically between species and require Jpx RNA in the mouse and the act of transcription of JPX locus in the human. Moreover, biogenesis of XIST is affected at different regulatory steps between these species. This study illustrates how diversification of LRGs modes of action during evolution provide opportunities for innovations within constrained gene regulatory networks.\n\nGraphical abstract\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=164 SRC=\"FIGDIR/small/689430v1_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (25K):\norg.highwire.dtl.DTLVardef@18b8583org.highwire.dtl.DTLVardef@ea605aorg.highwire.dtl.DTLVardef@15bc8aborg.highwire.dtl.DTLVardef@d38689_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗