Biology subjects

Golfier, S.

Publications and source records attributed to Golfier, S..

8 recordsLinked to original sources

bioRxiv2025

Dynamic switching of cell-substrate contact sites allows gliding diatoms to modulate the curvature of their paths

The directed motility of unicellular organisms is critical for their survival and ecological success, yet the mechanisms that enable rigid-walled cells to dynamically reorient and alter the shape of their trajectories remain poorly understood. Here, we investigate the gliding motility of Craspedostauros australis, a raphid pennate diatom that moves rapidly across submerged surfaces using an intracellular actomyosin motility complex and adhesive mucilage strand secretion. Using high-precision single-cell tracking, scanning electron microscopy (SEM), and interference reflection microscopy (IRM), we reveal how diatoms achieve diverse path curvatures by dynamically modulating the location of raphe-substrate contact and switching between one- and two-raphe contact gliding. Our results show that local curvature variations along the raphes dictate trajectory shapes, with one-raphe contact gliding producing highly curved paths, while two-raphe contact gliding results in paths of lower curvature. IRM imaging further confirms that transitions between these gliding modes underlie abrupt changes in path curvature and cell reorientation. This dynamic-raphe-switching mechanism is conserved across cell sizes and correctly predicts the increased path curvatures observed in smaller cells according to their more pronounced local raphe curvature. By quantitatively linking raphe geometry, cell-substrate attachment dynamics and motility patterns, our study provides insights into a novel motility mechanism that allows diatoms to adapt their movement to complex environments.

biophysics↗

bioRxiv2023

Novel YAP1/TAZ pathway inhibitors identified through phenotypic screening with potent anti-tumor activity via blockade of GGTase-I / Rho-GTPase signaling

This study describes the identification and target deconvolution of novel small molecule inhibitors of oncogenic YAP1/TAZ activity with potent anti-tumor activity in vivo. A high-throughput screen (HTS) of 3.8 million compounds was conducted using a cellular YAP1/TAZ reporter assay. Target deconvolution studies identified the geranylgeranyltransferase-I (GGTase-I) complex, as the direct target of YAP1/TAZ pathway inhibitors. The novel small molecule inhibitors block the activation of Rho-GTPases, leading to subsequent inactivation of YAP1/TAZ and inhibition of cancer cell proliferation in vitro. Multi-parameter optimization resulted in BAY-593, an in vivo probe with favorable PK properties, which demonstrated anti-tumor activity and blockade of YAP1/TAZ signaling in vivo. SIGNIFICANCEYAP1/TAZ have been shown to be aberrantly activated oncogenes in several human solid tumors, resulting in enhanced cell proliferation, metastasis and provision of a pro-tumorigenic microenvironment, making YAP1/TAZ targets for novel cancer therapies. Yet, the development of effective inhibitors of these potent oncogenes has been challenging. In this work, we break new ground in this direction through the identification of novel inhibitors of YAP1/TAZ activity. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=192 HEIGHT=200 SRC="FIGDIR/small/555331v2_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@4aac3forg.highwire.dtl.DTLVardef@728b6forg.highwire.dtl.DTLVardef@203a2eorg.highwire.dtl.DTLVardef@1cbc5f9_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTSO_LINovel YAP1/TAZ pathway inhibitors identified by phenotypic high-throughput screen C_LIO_LITarget deconvolution identifies GGTase-I as the direct target of the novel YAP1/TAZ pathway inhibitors C_LIO_LIGGTase-I inhibitors block Rho-GTPase signaling and downstream YAP1/TAZ C_LIO_LIGGTase-I inhibitor BAY-593 demonstrates potent anti-tumor activity in vivo C_LI

cancer biology↗

bioRxiv2020

Surface condensation of a pioneer transcription factor on DNA

In the last decade, extensive studies on the properties of non-membrane-bound compartments in the cellular cytoplasm have shown that concepts in phase separation drawn from physical chemistry can describe their formation and behaviour1-4. Current evidence also suggests that phase separation plays a role in the organization inside the cell nucleus5-8. However, the influence and role of DNA on the physical chemistry of phase separation is not well understood. Here, we are interested in the role of interactions between phase separating proteins and the DNA surface. The interaction of liquid phases with surfaces has been extensively studied in soft matter physics, in the context of macroscopic surfaces and non-biological liquids9-11. The conditions in the nucleus are different from those studied in conventional soft matter physics because DNA with a diameter of about 2 nm12 provides a microscopic surface, and liquid-like phases are complex mixtures of proteins subject to a myriad of biochemical modifications13. Transcriptional condensates, which are thought to serve as regulatory hubs in gene expression14-21, provide an accessible system to investigate the physics of condensates that emerge from DNA-protein and protein-protein interactions. These condensates are typically small22, and the mechanisms that determine their size are unknown. Whether they can be understood as phase separated compartments has been subject to debate23-26. Here, we use optical tweezers to directly observe the condensation of the pioneer transcription factor Klf427,28 on DNA in vitro. We demonstrate that Klf4 forms microphases that are enabled by interaction with the DNA surface. This sets their typical size and allows them to form below the saturation concentration for liquid-liquid phase separation. We combine experiment with theory to show that these microphases can be understood as forming by surface condensation on DNA via a switch-like transition similar to prewetting. Polymer surface mediated condensation reconciles several observations that were previously thought to be at odds with the idea of phase separation as an organizing principle in the nucleus.

biophysics↗

bioRxiv2020

Capillary forces drive pioneer transcription factor-mediated DNA condensation

Interactions between liquids and surfaces generate forces1,2 that are crucial for many processes in biology, physics, and engineering, including the motion of insects on the surface of water3, modulation of the material properties of spider silk4, and self-assembly of microstructures5. Recent studies have shown that cells assemble biomolecular condensates via phase separation6. In the nucleus, these condensates are thought to drive transcription7, heterochromatin formation8, nucleolus assembly9, and DNA repair10. Here, we show that the interaction between liquid-like condensates and DNA generates forces that might play a role in bringing distant regulatory elements of DNA together, a key step in transcriptional regulation. We combine quantitative microscopy, in vitro reconstitution, optical tweezers, and theory to show that the transcription factor FoxA1 mediates the condensation of a DNA-protein phase via a mesoscopic first- order phase transition. After nucleation, co-condensation forces drive growth of this phase by pulling non-condensed DNA. Altering the tension on the DNA strand enlarges or dissolves the condensates, revealing their mechanosensitive nature. These findings show that DNA condensation mediated by transcription factors could bring distant regions of DNA in close proximity, suggesting that this physical mechanism is a possible general regulatory principle for chromatin organization that may be relevant in vivo.

biophysics↗

bioRxiv2020

Top-down engineering of complex communities by directed evolution

Directed evolution has been used for decades to engineer biological systems from the top-down. Generally, it has been applied at or below the organismal level, by iteratively sampling the mutational landscape in a guided search for genetic variants of higher function. Above the organismal level, a small number of studies have attempted to artificially select microbial communities and ecosystems, with uneven and generally modest success. Our theoretical understanding of artificial ecosystem selection is still limited, particularly for large assemblages of asexual organisms, and we know little about designing efficient methods to direct their evolution. To address this issue, we have developed a flexible modeling framework that allows us to systematically probe any arbitrary selection strategy on any arbitrary set of communities and selected functions, in a wide range of ecological conditions. By artificially selecting hundreds of in-silico microbial metacommunities under identical conditions, we examine the fundamental limits of the two main breeding methods used so far, and prescribe modifications that significantly increase their power. We identify a range of directed evolution strategies that, particularly when applied in combination, are better suited for the top-down engineering of large, diverse, and stable microbial consortia. Our results emphasize that directed evolution allows an ecological structure-function landscape to be navigated in search for dynamically stable and ecologically and functionally resilient high-functioning communities.

evolutionary biology↗

bioRxiv2020

Spindle scaling is governed by cell boundary regulation of microtubule nucleation

Cellular organelles such as the mitotic spindle adjust their size to the dimensions of the cell. It is widely understood that spindle scaling is governed by regulation of microtubule polymerization. Here we use quantitative microscopy in living zebrafish embryos and Xenopus egg extracts in combination with theory to show that microtubule polymerization dynamics are insufficient to scale spindles and only contribute below a critical cell size. In contrast, microtubule nucleation governs spindle scaling for all cell sizes. We show that this hierarchical regulation arises from the partitioning of a nucleation inhibitor to the cell membrane. Our results reveal that cells differentially regulate microtubule number and length using distinct geometric cues to maintain a functional spindle architecture over a large range of cell sizes.

cell biology↗

bioRxiv2019

Cohesin and condensin extrude loops in a cell-cycle dependent manner

Chromatin undergoes a dramatic reorganization during the cell cycle1-3. In interphase, chromatin is organized into compartments and topological-associating domains (TADs) that are cell-type specific4-7, whereas in metaphase, chromosomes undergo large-scale compaction, leading to the loss of specific boundaries and the shutdown of transcription8-12. Loop extrusion by structural maintenance of chromosomes complexes (SMCs) has been proposed as a mechanism to organize chromatin in interphase and metaphase13-19. However, the requirements for chromatin organization in these cell phases are very different, and it is unknown whether loop extrusion dynamics and the complexes that extrude them also differ. Here, we used Xenopus egg extracts to reconstitute and image loop extrusion of single DNA molecules during the cell cycle. We show that loops form in both metaphase and interphase, but with distinct dynamic properties. Condensin extrudes asymmetric loops in metaphase, whereas cohesin extrudes symmetric loops in interphase. Our data show that loop extrusion is a general mechanism for the organization of DNA, with dynamic and structural properties that are molecularly regulated during the cell cycle.

cell biology↗

bioRxiv2019

Increasing demand for plasma membrane contributes to the energetic cost of early zebrafish embryogenesis.

How do early embryos apportion the resources stored in the sperm and egg? Recently, we established isothermal calorimetry (ITC) to measure heat dissipation by living zebrafish embryos and to estimate the energetics of specific developmental events. During the reductive cleavage divisions, the rate of heat dissipation increases from [~]60 nJ{middle dot}s-1 at the 2-cell stage to [~]90 nJ{middle dot}s-1 at the 1024-cell stage. Here we ask, which cellular process(es) drive these increasing energetic costs? We present evidence that the cost is due to the increase in the total surface area of all of the cells of the embryo. First, embryo volume stays constant during the cleavage stage, indicating that the increase is not due to growth. Second, the heat increase is blocked by nocodazole, which inhibits DNA replication, mitosis and cell division; this implicates some aspect of cell proliferation contributing to these costs. Third, the heat increase scales with total cell surface area rather than total cell number. Finally, the calculated costs of maintaining and assembling plasma membranes and associated proteins probably accounts for a significant proportion of the heat increase. Thus, the cells membrane is likely to contribute significantly to the total energy budget of the embryo.\n\nHighlight summary for TOCRodenfels et al. measure the energetic costs of early zebrafish development, using calorimetry. Embryonic heat dissipation increases, but, more slowly than the number of cells during early cleavage stage development. Instead, the heat dissipation scales with the energetic cost associated with maintaining and producing new plasma membrane.

developmental biology↗