Biology subjects

Pettko-Szandtner, A.

Publications and source records attributed to Pettko-Szandtner, A..

9 recordsLinked to original sources

bioRxiv2026

Revamped transposon-induced hepatocellular carcinoma model reveals deep similarities of cancer-driver landscapes across mice and humans

Genome-scale cancer-driver discovery is limited by statistical uncertainty in driver calling and by experimental constraints on mutations available for selection. We developed 3xfOnc3 - a three-frame Sleeping Beauty (SB) mutagenesis system designed to broaden functional perturbations and reduce integration biases of traditional SB screens - and tested it in vivo in mouse liver. Within 12 months, 60% of mice developed heterogeneous hepatocellular tumors. Tumor-selected integrations were interpreted against an empirical reference from SB-based therapeutic gene delivery to hepatocytes, enabling correction for gene targetability. Background-aware filtering prioritized 315 driver candidates, including 243 protein-coding genes. Tumors were multiclonal, and identical integration-marked lineages expanded differently across lesions, supporting context-dependent clonal expansion. SB hits within young L1 subfamily members were selectively enriched in tumors. Human orthologues of candidate drivers were enriched for Cancer Gene Census genes and protein-altering pan-cancer mutations. Together, 3xfOnc3 reveals a background-corrected driver landscape linking driver selection to clonal tumor evolution and cross-species cancer relevance.

cancer biology↗

bioRxiv2026

The multifunctional scaffold protein Small ovary couples piRNA-guided transposon recognition to nuclear RNA decay and heterochromatin formation

The piRNA pathway maintains genome integrity by silencing transposons cotranscriptionally in the nucleus through recognition of nascent transposon RNAs and recruitment of endogenous transcriptional and chromatin-level repressive mechanisms to transposon loci. However, the molecular link between the SFiNX complex, which recognizes nascent transposon RNA, and downstream effector complexes has remained elusive. Here, we demonstrate that the Small ovary (Sov) protein mediates this connection. By mapping the functional activities of its structural elements, we reveal that Sov contributes to transposon silencing through two distinct molecular mechanisms. First, Sov specifically directs nascent transposon transcripts toward nuclear RNA exosome-mediated degradation by physically interacting with the RNA decay factor TEsup1. Second, Sov directly binds the heterochromatin protein HP1a via multiple conserved motifs and undergoes phase separation, facilitating heterochromatin formation and genome-wide gene repression. Genetic analyzes of sov mutants reveal that these functions are separable: RNA-mediated transcriptional silencing is essential for piRNA pathway activity, while phase separation-dependent heterochromatin regulation is critical for stable transposon repression. We propose that Sov acts as a molecular scaffold in piRNA-guided transposon silencing, integrating transposon recognition with cotranscriptional RNA decay and chromatin-based regulatory pathways.

molecular biology↗

bioRxiv2026

Flightless I and LRRFIP work together to regulate lateral growth of the sarcomeres in Drosophila

Myofibrils are structurally highly conserved elements of the cardiac and striated muscles. The striking commonalities in their basic organization principles emerge during myofibrillogenesis when the initially formed premyofibrils grow in length and width to attain their final dimensions, characteristic of each muscle type. Although the molecular composition of the myofibrils is well known, the mechanisms governing their growth remain poorly understood, particularly those driving peripheral thickening. Here, we show that two cardiac disease associated proteins, Flightless I and LRRFIP, are required for lateral integration of the myofilaments that is essential for circumferential myofibril growth in the Drosophila flight muscle. Genetic and biochemical analysis reveal that these proteins form multimeric complexes enriched at the barbed end of the actin filaments. Furthermore, we found that the Flightless I/LRRFIP complex acts in a formin dependent manner. Together, our findings demonstrate that Flightless I and LRRFIP cooperate to promote the spatially controlled integration of peripheral actin filaments at the Z-disc, uncovering a key step in myofibril maturation.

cell biology↗

bioRxiv2026

Complex regulation of RETINOBLASTOMA-RELATED's interactions with E2Fs via phosphorylation

Arabidopsis RETINOBLASTOMA-RELATED (RBR) regulates cell proliferation by interacting with E2F transcription factors and DIMERIZATION PARTNER, RB-LIKE, E2F AND MULTI-VULVAL CLASS B COMPLEX (DREAM) components. Although CDK-CYCD phosphorylation is believed to affect RBRs E2F-binding capacity, the precise phosphorylation events inhibiting RBRs cell cycle function remain unclear. This study found RBR phosphorylated at 13 of 16 CDK sites in Arabidopsis, with many phosphorylated forms still binding E2Fs. In contrast, multi-phosphorylated RBR forms with phosphorylated 911S site in Arabidopsis thaliana and corresponding sites in Medicago truncatula or Brassica napus do not co-purify with E2Fs and DREAM components but interact with RNA-binding proteins involved in post-transcriptional regulation through ribosomal biogenesis and protein translation. The 911S phosphorylation is high in proliferating cells and rapidly diminishes under DNA damage conditions, indicating its role in switching from proliferation to quiescence under stress. However, molecular modelling implies that this site is not accessible for phosphorylation if RBR is in complex with E2Fs. These findings suggest that different phosphorylation events inhibit RBRs capacity to form complexes with E2Fs and to release E2Fs from RBR inhibition. We posit that multi-site phosphorylation coupled to 911S impedes free RBRs binding to E2Fs and DREAM components, but this is not the initial inhibitory phosphorylation contributing to the disruption of RBR-E2F-DP complexes. Rather, it facilitates RBR interaction with proteins involved in post-transcriptional cell cycle regulation.

plant biology↗

bioRxiv2024

Functional framework of the kinetochore and spindle assembly checkpoint in Arabidopsis thaliana

The kinetochore, critical for accurate chromosome segregation and genome stability in eukaryotes, comprises the Constitutive Centromere Associated Network (CCAN) and the KMN network. In animals, the CCAN associates with centromeric nucleosomes throughout the cell cycle, while the KMN network assembles at kinetochores during M phase, binding spindle microtubules and serving as a platform for the spindle assembly checkpoint (SAC) complex. Despite conserved functions, kinetochore components vary across organisms. This study investigates the subcellular localization and interaction maps of core kinetochore components in Arabidopsis thaliana, finding that only CENP-C of the four conserved CCAN components localizes to kinetochores, while all KMN components consistently localize to the kinetochore throughout the cell cycle. Immunoprecipitation assays revealed interactions between core kinetochore proteins and regulators involved in DNA replication, histone modification, and chromatin remodeling, suggesting that the kinetochore may also function outside of M phase. Examining interactions between kinetochore and SAC components elucidates plant-specific SAC localization mechanisms providing a functional framework for understanding plant kinetochores and offering new insights into SAC regulation in plants.

cell biology↗

bioRxiv2024

LIFERING, an E3 ligase, targets the acyl-CoA dehydrogenase-like protein IBR3, for ubiquitination and coordinates cell proliferation and cell death upon DNA damage

Plants rapidly respond to environmental changes to ensure an optimal balance between growth and survival with intact genome. Here, we show that a DNA damage response gene, which we named LIFERING, is under the direct and independent regulation of ATM/ATR-SOG1 and RBR pathways. We demonstrate that LIFERING upon DNA damage plays an essential role in maintaining the balance between cell proliferation and cell death. Downstream of RBR, it is required to maintain proliferation, and in response to DNA damaging agents it initiates a cell death accompanied by rapid elongation and differentiation of the transit amplifying cells in the root meristem. LIFERING is a RING-between-RING E3 ligase; its ligase activity is dependent on the Cys392 residue located in the BRcat domain, responsible for the coordination of zinc ion binding. Using proximity labelling, we identified the acyl-CoA dehydrogenase-like protein IBR3, which is involved in the conversion of indole-3-butyric acid (IBA) to indole-3-acetic acid (IAA), as one of its targets. We provide evidence that IBR3 is ubiquitinated at several Lys residues in the presence of LIFERING. Our findings show that LIFERING rapidly responds to DNA damage and via ubiquitination of IBR3, is likely to be involved in the regulation of free-auxin level, indicating a link between DNA damage response and auxin regulation in the root.

plant biology↗

bioRxiv2024

Retinoblastoma-related (RBR) has both canonical and non-canonical regulatory functions during thermo-morphogenic responses in Arabidopsis seedlings

Warm temperatures accelerate plant growth, but the underlying molecular mechanism is not fully understood. Here, we show that increasing the temperature from 22{degrees}C to 28{degrees}C rapidly activates proliferation in the apical shoot and root meristems of wild-type Arabidopsis seedlings. We found that one of the central regulators of cell proliferation, the cell cycle inhibitor RETINOBLASTOMA-RELATED (RBR), is suppressed by warm temperatures. RBR became hyper-phosphorylated at a conserved CYCLIN-DEPENDENT KINASE (CDK) site in young seedlings growing at 28{degrees}C, in parallel with the stimulation of the expressions of the regulatory CYCLIN D/A subunits of CDK(s). Interestingly, while under warm temperatures ectopic RBR slowed down the acceleration of cell proliferation, it triggered elongation growth of post-mitotic cells in the hypocotyl. In agreement, the central regulatory genes of thermomorphogenic response, including PIF4 and PIF7, as well as their downstream auxin biosynthetic YUCCA genes (YUC1-2 and YUC8-9) were all up-regulated in the ectopic RBR expressing line but down-regulated in a mutant line with reduced RBR level. We suggest that RBR has both canonical and non-canonical functions under warm temperatures to control proliferative and elongation growth, respectively.

plant biology↗

bioRxiv2024

TFIIS is required for reproductive development and thermal adaptation in barley

Regulation of transcriptional machinery and its adaptive role under different stress conditions are studied extensively in the dicot model plant Arabidopsis, but our knowledge on monocot species remains elusive. TFIIS is an RNA polymerase II associated transcription elongation co-factor. Previously it was shown that TFIIS ensures efficient transcription elongation that is necessary for heat stress survival in A. thaliana. However, the function of TFIIS has not been analysed in monocots. In the present work, we have generated and studied independent tfIIscrispr mutant barley lines. We show that, TFIIS is needed for reproductive development and heat stress survival in barley. The molecular basis of HS-sensitivity of tfIIs mutants is the retarded expression of heat stress protein transcripts, that leads to late accumulation of HSP chaperones, enhanced proteotoxicity and ultimately to lethality. We also show that TFIIS is induced and autoregulated in response to heat, supporting a conserved adaptive function of these control elements for plant thermal adaptation. In sum, our results are a step forward for the better understanding of transcriptional machinery regulation in monocot crops.

plant biology↗

bioRxiv2018

Drosophila small ovary gene ensures germline stem cell maintenance and differentiation by silencing transposons and organising heterochromatin

Self-renewal and differentiation of stem cells is one of the fundamental biological phenomena relying on proper chromatin organisation. In our study, we describe a novel chromatin regulator encoded by the Drosophila small ovary (sov) gene. We demonstrate that sov is required in both the germline stem cells (GSCs) and the surrounding somatic niche cells to ensure GSC survival and differentiation. Sov maintains niche integrity and function by repressing transposon mobility, not only in the germline, but also in the soma. Protein interactome analysis of Sov revealed a physical interaction between Sov and HP1a. In the germ cell nuclei, Sov co-localises with HP1a, suggesting that Sov affects transposon repression as a component of the heterochromatin. In a position effect variegation assay, we found a dominant genetic interaction between sov and HP1a, indicating their functional cooperation in promoting the spread of heterochromatin. An in vivo tethering assay and FRAP analysis revealed that Sov enhances heterochromatin formation by supporting the recruitment of HP1a to the chromatin. We propose a model in which sov maintains GSC niche integrity by regulating piRNA-mediated transposon silencing as a heterochromatin regulator.\n\nSummary statementSmall ovary maintains the integrity of the stem cell niche by regulating piRNA-mediated transposon silencing acting as a key component of the heterochromatin.

developmental biology↗