Biology subjects

Prevo, B.

Publications and source records attributed to Prevo, B..

9 recordsLinked to original sources

bioRxiv2025

Calyculin A Induces Premature Chromosome Condensation and Chromatin Compaction in G1-Phase HeLa Cells without Histone H1 Phosphorylation

We show here that treatment of HeLa cells with calyculin A, an inhibitor of Protein Phosphatases 1 and 2A, induces premature chromosome condensation (PCC) at any point in interphase of the cell cycle. Chromosomes in G1-phase PCC closely resemble metaphase chromatids in the light microscope, and measurements using FLIM-FRET show that they have the same level of chromatin compaction as metaphase chromosomes. However, histone H1 is not phosphorylated in G1- or early S-phase PCC. These results suggest that H1 phosphorylation is not required for mitotic chromosome condensation and chromatin compaction. They also confirm that Cdk1/cyclin B, which directly phosphorylates histone H1, is not active in G1 and thus is not essential for G1- PCC. We suggest that induction of G1-PCC involves protein kinases or other factors that are either held in an inactive state by protein phosphatases, or constitutively active but countered by phosphatases. The same factors may be involved in the onset of normal mitosis, becoming active when protein phosphatases are downregulated. Induction of PCC with calyculin A should provide a useful system for identifying and studying the biochemical pathways that are required for mitotic chromosome compaction, nuclear envelope breakdown, and other events of mitosis.

cell biology↗

bioRxiv2025

RIF1 orchestrates a multi-step restoration of post-replicative H3K9me3

DNA replication causes the dilution of parental histones along with their specific post-translational modifications. The kinetics of restoring these marks on newly incorporated histones dictate how quickly genomic domains regain their epigenetic identity after replication. H3K9me3 is restored extremely slowly; the process of reconstitution, to achieve the pre-replication levels, continues throughout the following G1 phase. The molecular mechanisms behind this slow reconstitution are unknown. We show here that RIF1s reassociation with heterochromatin during mitotic exit is required to set up a chromatin environment permissive for histone methyltransferases to resume H3K9me3 deposition. RIF1 facilitates the recruitment of SUV39H1, HP1 and HP1{beta} and is required for the increased tri-methylation of H3K9 that occurs during G1 phase. RIF1 is also indispensable for recruiting Protein Phosphatase 1 (PP1) to heterochromatin, and the interaction between RIF1 and PP1 is essential for the maintenance of H3K9me3 levels. In addition, RIF1-PP1 complex temporally restrains the activity of Aurora kinase at heterochromatin, ensuring that phosphorylation of H3S10 does not precede replication. This creates a time- window permissive for SUV39Hs to initiate the reinstatement of H3K9me3.

cell biology↗

bioRxiv2024

DYF-5 regulates intraflagellar transport by affecting train turnaround

Intraflagellar transport (IFT) coordinates the transport of cargo in cilia and is essential for ciliary function. CILK1 has been identified as a key regulator of IFT. The mechanism by which it acts has, however, remained unclear. In this study, we use fluorescence imaging and single-molecule tracking in the phasmid cilia of live C. elegans to study the effect of the CILK1 homolog DYF-5 on the dynamics of the IFT. We show that in the absence of DYF-5, IFT components accumulate at the ciliary tip. kinesin-II is no longer restricted to the proximal segment of the cilium but is present all throughout the cilium, while its velocity is different from that of OSM-3. The frequency of IFT trains is reduced and in particular retrograde trains were rarely observed. In the absence of DYF-5, retrograde transport is vastly reduced, resulting in the accumulation of IFT components at the tip and depletion at the base. The latter results in impeded anterograde train assembly, resulting in fewer trains with irregular composition. Our results show that DYF-5 plays a key role in regulating the turnarounds of IFT trains at the ciliary tip.

molecular biology↗

bioRxiv2024

SID-2 localises to extracellular vesicles in parasitic nematodes and does not function in environmental RNAi

In the free-living nematode Caenorhabditis elegans the transmembrane protein SID-2 imports double-stranded RNA into intestinal cells to trigger systemic RNA interference (RNAi), allowing organisms to sense and respond to environmental cues such as the presence of pathogens. This process, known as environmental RNAi, has not been observed in the most closely related parasites that are also within clade V. Previous sequence-based searches failed to identify sid-2 orthologs in available clade V parasite genomes. In this study we identified sid-2 orthologues in these parasites using genome synteny and protein structure-based comparison, following identification of a SID-2 orthologue in extracellular vesicles from the murine intestinal parasitic nematode Heligmosomoides bakeri. Expression of GFP-tagged H. bakeri SID-2 in C. elegans showed comparable localisation to the intestinal apical membrane as seen for GFP-tagged C. elegans SID-2 and further showed mobility in intestinal cells in vesicle-like structures. We tested the capacity of H. bakeri SID-2 to functionally complement environmental RNAi in a C. elegans SID-2 null mutant and show that H. bakeri SID-2 does not rescue the phenotype in this context. Therefore, our work identifies SID-2 as a highly abundant nematode EV protein whose ancestral function may be unrelated to environmental RNA and rather highlights an association with extracellular vesicle-mediated communication in free-living and parasitic nematodes.

evolutionary biology↗

bioRxiv2024

The Outer Kinetochore Proteins KNL-1 and Ndc80 complex are Required to Pattern the Central Nervous System

The KMN (Knl1/Mis12/Ndc80) network at the kinetochore, primarily known for its role in chromosome segregation, has been shown to be repurposed during neurodevelopment. Here, we investigate the underlying neuronal mechanism and show that the KMN network is essential to establish the proper axonal organization within the C. elegans head nervous system. Post-mitotic degradation of KNL-1, which acts as a scaffold for signaling and has microtubule-binding activities at the kinetochore, led to disorganized ganglia and aberrant placement and organization of axons in the nerve ring - an interconnected axonal network. Through gene-replacement approaches, we demonstrate that the signaling motifs within KNL-1, responsible for recruiting the protein phosphatase 1, and activating the spindle assembly checkpoint are required for neurodevelopment. Interestingly, while the microtubule-binding activity is crucial to KMNs neuronal function, microtubule dynamics and organization were unaffected in the absence of KNL-1. Instead, the NDC-80 microtubule-binding mutant displayed notable defects in axon bundling during nerve ring formation, indicating its role in facilitating axon-axon contacts. Overall, these findings provide evidence for a non-canonical role for the KMN network in shaping the structure and connectivity of the nervous system in C. elegans during brain development.

cell biology↗

bioRxiv2023

The Kinetochore Protein KNL-1 Regulates Actin Cytoskeleton Dynamics to Promote Dendrite Branching in Sensory Neurons

The function of the nervous system is intimately tied to its complex and highly inter-connected architecture. Precise control of dendritic branching in individual neurons is central to building the complex structure of the nervous system. Here we show that the kinetochore protein KNL-1 and its associated KMN (Knl1/Mis12/Ndc80 complex) network partners, typically known for their role in chromosome-microtubule coupling during mitosis, control dendrite branching in the C. elegans mechanosensory PVD neuron. KNL-1 restrains excess dendritic branching and promotes contact-dependent repulsion events, ensuring robust sensory behavior and preventing premature neurodegeneration. Unexpectedly, KNL-1 loss resulted in significant alterations of the actin cytoskeleton alongside changes in microtubule dynamics within dendrites. We show that KNL-1 modulates F-actin dynamics to generate proper dendrite architecture, and that its N-terminus can initiate F-actin assembly. These findings reveal that the post-mitotic neuronal KMN network acts to shape the developing nervous system by regulating the actin cytoskeleton and provide new insight into the mechanisms controlling dendrite architecture.

neuroscience↗

bioRxiv2023

Kinetochore dynein is sufficient to biorient chromosomes and remodel the outer kinetochore

Multiple microtubule-directed activities concentrate on chromosomes during mitosis to ensure their accurate distribution to daughter cells. These activities include couplers and dynamics regulators localized at the kinetochore, the specialized microtubule interface built on centromeric chromatin, as well as motor proteins recruited to kinetochores and to mitotic chromatin. Here, we describe an in vivo reconstruction approach in which the effect of removing the major microtubule-directed activities on mitotic chromosomes is compared to the selective presence of individual activities. This approach revealed that the kinetochore dynein module, comprised of the minus end-directed motor cytoplasmic dynein and its kinetochore-specific adapters, is sufficient to biorient chromosomes and to remodel outer kinetochore composition following microtubule attachment; by contrast, the kinetochore dynein module is unable to support chromosome congression. The chromosome-autonomous action of kinetochore dynein, in the absence of the other major microtubule-directed factors on chromosomes, rotates and orients a substantial proportion of chromosomes such that their sister chromatids attach to opposite spindle poles. In tight coupling with orientation, the kinetochore dynein module drives removal of outermost kinetochore components, including the dynein motor itself and spindle checkpoint activators. The removal is independent of the other major microtubule-directed activities and kinetochore-localized protein phosphatase 1, suggesting that it is intrinsic to the kinetochore dynein module. These observations indicate that the kinetochore dynein module has the ability coordinate chromosome biorientation with attachment state-sensitive remodeling of the outer kinetochore that facilitates cell cycle progression.

cell biology↗

bioRxiv2017

Dynactin Binding To Tyrosinated Microtubules Promotes Centrosome Centration In C. Elegans By Enhancing Dynein-Mediated Organelle Transport

The microtubule-based motor dynein generates pulling forces for centrosome centration and mitotic spindle positioning in animal cells. How the essential dynein activator dynactin regulates these functions of the motor is incompletely understood. Here, we dissect the role of dynactins microtubule binding activity, located in p150s CAP-Gly domain and an adjacent basic patch, in the C. elegans zygote. Using precise mutants engineered by genome editing, we show that microtubule tip tracking of dynein-dynactin is dispensable for targeting the motor to the cell cortex and for generating cortical pulling forces. Instead, p150 CAP-Gly mutants inhibit cytoplasmic pulling forces responsible for centration of centrosomes and attached pronuclei. The centration defects are mimicked by mutations of the C-terminal tyrosine of -tubulin, and both p150 CAP-Gly and tubulin tyrosination mutants decrease the frequency of organelle transport from the cell periphery towards centrosomes during centration. In light of recent work on dynein-dynactin motility in vitro, our results suggest that p150 GAP-Gly domain binding to tyrosinated microtubules promotes initiation of dynein-mediated organelle transport in the dividing embryo, and that this function of dynactin is important for generating robust cytoplasmic pulling forces for centrosome centration.

cell biology↗

bioRxiv2017

A toolkit for tissue-specific protein degradation in C. elegans

Proteins essential for embryo production, cell division, and early embryonic events are frequently re-utilized later in embryogenesis, during organismal development, or in the adult. Examining protein function across these different biological contexts requires tissue-specific perturbation. Here, we describe a method that utilizes expression of a fusion between a GFP-targeting nanobody and SOCS-box containing ubiquitin ligase adaptor to target GFP tagged proteins for degradation. When combined with endogenous locus GFP tagging by CRISPR-Cas9 or rescue of a null mutant with a GFP fusion, this approach enables routine and efficient tissue-specific protein ablation. We show that this approach works in multiple tissues--the epidermis, intestine, body wall muscle, sensory neurons, and touch neurons--where it recapitulates expected loss-of-function mutant phenotypes. The transgene toolkit and the strain set described here will complement existing approaches to enable routine analysis of the tissue-specific roles of C. elegans proteins.

developmental biology↗