Biology subjects

Maddox, P.

Publications and source records attributed to Maddox, P..

6 recordsLinked to original sources

bioRxiv2026

Coordinated chromosome motion emerges from mechanical coupling mediated by the physical spindle environment

During metaphase, chromosomes undergo oscillatory motion and exhibit distance-dependent coordinated movement with neighboring chromosomes within the spindle. However, the physical mechanism that gives rise to coordinated chromosome motion remains unclear. Here, we combine quantitative live-cell imaging in PTK1 cells, targeted perturbations of spindle microtubules and chromatin, and minimal mechanical modeling to uncover the mechanical basis of chromosome coordination during metaphase. We show that chromosome oscillations are dampened by stabilizing microtubules or by decondensing chromatin, yet inter-chromosomal coordination is preserved. The dissociation between chromosome oscillations and chromosome coordination suggests that coordination can arise from forces transmitted through the spindle environment. To test this idea, we developed a minimal mechanical model in which oscillating chromosome pairs are coupled through transient inter-chromosomal springs, while oscillations of each chromosome pair are generated by feedback between kinetochore-microtubule dynamics and centromere elasticity. The model demonstrates that stochastic mechanical connections are sufficient to generate correlated chromosome motion. To quantify chromosome coordination in a manner that reflects the mechanical properties of the surrounding spindle environment, we employed a microrheology-inspired analysis of time-lagged chromosome displacements. This framework reveals that microtubules and chromatin play distinct mechanical roles: microtubules primarily determine the spatial range and temporal build-up of coordination, while chromatin tunes its strength. Together, our results establish coordinated chromosome motion as an emergent mechanical property of the mitotic spindle, mediated by its viscoelastic properties and collective force transmission.

cell biology↗

bioRxiv2024

Cellular context specific tuning of actomyosin ring contractility within a common cytoplasm

Actomyosin rings are specializations of the non-muscle actomyosin cytoskeleton that drive cell shape changes during division, wound healing, and other events. Contractile rings throughout phylogeny and in a range of cellular contexts are built from conserved components including non-muscle myosin II, actin filaments, and crosslinking proteins. To explore whether diverse actomyosin rings generate contractile force and close via a common mechanism, we studied three instances of ring closure within the continuous cytoplasm of the C. elegans syncytial oogenic germline: mitotic cytokinesis of germline stem cells, apoptosis of meiotic compartments, and cellularization of oocytes. The three ring types exhibited distinct closure kinetics and component protein abundance dyanmics. We formulated a physical model to relate measured closure speed and molecular composition dynamics to ring active stress and viscosity. We conclude that these ring intrinsic factors vary among the ring types. Our model suggests that motor and non-motor crosslinkers abundance and distribution along filaments are important to recapitulate observed closure dynamics. Thus, our findings suggest that across ring closure contexts, fundamental contractile mechanics are conserved, and the magnitude of contractile force is tuned via regulation of ring component abundance and distribution. These results motivate testable hypotheses about cytoskeletal regulation, architecture, and remodeling.

cell biology↗

bioRxiv2023

Septins throughout phylogeny are predicted to have a transmembrane domain, which in Caenorhabditis elegans is functionally important.

Septins, a conserved family of filament-forming proteins, contribute to eukaryotic cell division, polarity, and membrane trafficking. Septins scaffold other proteins to cellular membranes, but it is not fully understood how septins associate with membranes. We identified and characterized an isoform of Caenorhabditis elegans septin UNC-61 that was predicted to contain a transmembrane domain (TMD). The TMD isoform is expressed in a subset of tissues where the known septins were known to act, and TMD function was required for tissue integrity of the egg-laying apparatus. We found predicted TMD-containing septins across much of opisthokont phylogeny and demonstrated that the TMD-containing sequence of a primate TMD-septin is sufficient for localization to cellular membranes. Together, our findings reveal a novel mechanism of septin-membrane association with profound implications for septin dynamics and regulation.

cell biology↗

bioRxiv2022

Trajectory classification method for anchored molecular motor-biopolymer interactions in the C. elegans first mitosis.

During zygotic mitosis, forces generated at the cell cortex are required for the separation and migration of paternally provided centrosomes, pronuclear migration, proper segregation of genetic material, and successful cell division. Identification of individual cortical force generating units in vivo is necessary to study the regulation of microtubule dependent force generation throughout the cell cycle, to further understanding of asymmetric cell division, and to identify the molecular mechanism of force generation. Here we present a method to determine both the location and relative number of microtubule dependent cortical force generating units using single molecule imaging of fluorescently labelled dynein. Dynein behavior is modeled to differentiate and categorize trajectories that correspond to that which is cortically bound and interacting with a microtubule, and is cortically bound and not interacting with a microtubule. The categorization strategy recapitulates well known force asymmetries in the first mitosis of the C. elegans embryo. To evaluate the robustness of categorization, we RNAi depleted the microtubule subunit TBA-2 resulting in reduction of the number of trajectories categorized as engaged with a microtubule. This technique will be a valuable tool to provide new insight to the molecular mechanisms of dynein cortical force generation and its regulation as well as other instances wherein anchored motors interact with biopolymers (eg. Actin, tubulin, DNA).

cell biology↗

bioRxiv2019

POT-1 telomere binding protein promotes a novel form of Transgenerational Epigenetic Inheritance

Transgenerational Epigenetic Inheritance occurs when gametes transmit forms of information without altering genomic DNA1. Although deficiency for telomerase in human families causes transgenerational shortening of telomeres2, a role for telomeres in Transgenerational Epigenetic Inheritance is unknown. Here we show that Protection Of Telomeres 1 (Pot1) proteins, which interact with single-stranded telomeric DNA3,4, function in gametes to regulate developmental expression of telomeric foci for multiple generations. C. elegans POT-1 and POT-25,6 formed abundant telomeric foci in adult germ cells that vanished in 1-cell embryos and gradually accumulated during development. pot-2 mutants displayed abundant POT-1::mCherry foci throughout development. pot-2 mutant gametes created F1 cross-progeny with constitutively abundant POT-1::mCherry and mNeonGreen::POT-2 foci, which persisted for 6 generations but did not alter telomere length. pot-1 mutant and pot-2; pot-1 double mutant gametes gave rise to progeny with constitutively diminished Pot1 foci. Genomic silencing and small RNAs potentiate many transgenerational effects7 but did not affect Pot1 foci. We conclude that C. elegans POT-1 functions at telomeres of pot-2 mutant gametes to create constitutively high levels of Pot1 foci in future generations. As regulation of telomeres and Pot1 have been tied to cancer8,9, this novel and highly persistent form of Transgenerational Epigenetic Inheritance could be relevant to human health.

genetics↗

bioRxiv2018

Centrosome-nuclear envelope tethering and microtubule motor-based pulling forces collaborate in centrosome positioning during mitotic entry

Centrosome positioning relative to the nucleus and cell shape is highly regulated across cell types, during cell migration and during spindle formation in cell division. Across most sexually reproducing animals, centrosomes are provided to the oocyte through fertilization and must be positioned properly to establish the zygotic mitotic spindle. How centrosomes are positioned in space and time through the concerted action of key mitotic entry biochemical regulators including Protein Phosphatase 2A (PP2A-B55/SUR-6), biophysical regulators including Dynein and the nuclear lamina is unclear. Here, we uncover a role for PP2A-B55/SUR-6 in regulating centrosome positioning. Mechanistically, PP2A-B55/SUR-6 regulates nuclear size prior to mitotic entry, in turn affecting nuclear envelope-based Dynein density and motor capacity. Using computational simulations, PP2A-B55/ SUR-6 regulation of nuclear size and nuclear envelope Dynein density were both predicted to be required for proper centrosome positioning. Conversely, compromising nuclear lamina integrity led to centrosome detachment from the nuclear envelope and migration defects. Removal of PP2A-B55/SUR-6 and the nuclear lamina simultaneously further disrupted centrosome positioning, leading to unseparated centrosome pairs dissociated from the nuclear envelope. Taken together, we propose a model in which centrosomes migrate and are positioned through the concerted action of nuclear envelope-based Dynein pulling forces and cen-trosome-nuclear envelope tethering.

cell biology↗