Biology subjects

Glotzer, M.

Publications and source records attributed to Glotzer, M..

10 recordsLinked to original sources

bioRxiv2026

The Rap1 GTPase performs two separable functions during cellularization to enable ventral furrow formation

Morphogenetic processes involve dynamic cell-level events, such as contractility, shape changes, and adhesion between cells and extracellular structures. These cell-level changes require intercellular coordination in order to generate the appropriate tissue-level output. Although the repertoire of these cell-level changes is limited, these processes are reused serially during development to generate diverse tissue-level transformations. Dissecting any one of them benefits from perturbations controlled with high spatiotemporal resolution. Despite extensive analysis of ventral furrow formation, a model gastrulation event in the early Drosophila embryo, it remains unclear how tissue-level events are orchestrated at the molecular level. We therefore developed a biosensor and optogenetic tools for spatiotemporal modulation of Rap1, a small GTPase known to be required for ventral furrow formation. Using the biosensor, we show that Rap1 activity declines in ventral cells as the furrow forms. Optogenetic dissection of Rap1 activity reveals that acute inhibition during furrowing has little effect. Instead, Rap1 contributes to furrowing through two separable functions during the preceding process, cellularization: it is continuously required for efficient membrane ingression, and transiently required to nucleate the adherens junctions that later coordinate contractility across the ventral epithelium.

cell biology↗

bioRxiv2024

Phylogenetic analysis of Centralspindlin and Ect2 provides mechanistic insights into the emergence of Metazoa and multicellularity

Obligate multicellularity evolved at least 5 times in eukaryotes, including at the origin of Metazoa 1, 2. The molecular events leading to the acquisition of multicellularity are not understood in any lineage. Here, I present an integrated analysis into the emergence of three regulators of cytokinesis and the Metazoan kingdom. Phylogenetic analysis and structural modeling indicate that three interacting essential regulators of cytokinesis, Kif23, Cyk4, and Ect2, are highly conserved across all Metazoa. These proteins cooperate to link the plane of cell division with the position of the spindle during anaphase and subsequently nucleate the assembly of stable intercellular bridges 3-6, structures prevalent in Metazoan germlines 7. The closest relatives of Metazoa, Choanoflagellata, encode Kif23 and Ect2 orthologs. In contrast, choanoflagellate species variably encode members of paralogous sets of proteins related to Cyk4, some of which are predicted to interact with Kif23. These findings, in conjunction with prior knowledge, suggests that the evolutionary refinement of these three cytokinetic regulators was a proximal prerequisite for the evolution of defining features of Metazoa.

evolutionary biology↗

bioRxiv2024

A minimal mathematical model for polarity establishment and centralsplindlin-independent cytokinesis

Cell polarization and cytokinesis are fundamental processes in organismal development. In the Caenorhabditis elegans model system, both processes are partially driven by a local inhibition of contractility at the cell poles. Polarization is triggered by centrosome-directed, local inhibition of cortical contractility at what becomes the posterior pole, while cytokinesis occurs when spindle elongation-dependent astral relaxation combines with centralspindlin-induced accumulation of myosin at the cell equator. During both processes, Aurora A (AIR-1) kinase is activated on centrosomes and diffuses to the cortex where it inhibits the guanine nucleotide exchange factor (GEF) ECT-2, attenuating RHO-1 activation and actomyosin-based contractility. While these biochemical processes have been characterized experimentally, a quantitative understanding of how this circuit drives cortical dynamics in polarization and cytokinesis is still lacking. Here, we construct a mathematical model to test whether a minimal set of well characterized, essential elements are necessary and sufficient to explain the spatiotemporal dynamics of AIR-1, ECT-2, and myosin during polarization and cytokinesis of C. elegans. We show that robust establishment of polarity can be obtained in response to a weak AIR-1 signal, and demonstrate the relevance of rapid ECT-2 exchange and a persistent AIR-1 cue during polarization. In the minimal model, the rapid turnover of ECT-2 causes a quasi-steady response to changes in the AIR-1 signal, and transient asymmetries are not self-sustaining. After tuning the model for polarization, we demonstrate that it can accurately predict ECT-2 accumulation during cytokinesis, suggesting a quantitative similarity between the two processes.

cell biology↗

bioRxiv2023

Apical polarity and actomyosin dynamics regulate Hippo signaling by controlling Kibra subcellular localization

Cell polarity and actomyosin networks are key features that organize cells of epithelial tissues and are known to regulate tissue growth. However, the mechanisms by which polarity cues and actomyosin cytoskeleton influence intracellular signaling cascades that control growth remain poorly understood. The Hippo pathway is an evolutionarily conserved regulator of tissue growth and is known to integrate inputs from both polarity and actomyosin components. An upstream activator of the Hippo pathway, Kibra, localizes into distinct pools at the junctional and medial regions of the apical cortex in epithelial cells, and medial accumulation was shown to promote Kibra activity. Here, we demonstrate that cortical Kibra distribution is controlled by a tug of war between apical polarity and actomyosin dynamics. We show that while the apical polarity network, in part via aPKC, tethers Kibra at the junctional cortex to silence its activity, medial actomyosin flows promote Kibra-mediated Hippo complex formation at the medial cortex, thereby activating the Hippo pathway. This study provides a mechanistic understanding of the relationship between the Hippo pathway, polarity, and actomyosin cytoskeleton and offers novel insights into how fundamental features of epithelial tissue architecture can serve as inputs into signaling cascades that control tissue growth, patterning, and morphogenesis.

cell biology↗

bioRxiv2022

Aurora A and cortical flows promote polarization and cytokinesis by inducing asymmetric ECT-2 accumulation

In the early C. elegans embryo, cell polarization and cytokinesis are interrelated yet distinct processes. Here, we sought to understand a poorly understood aspect of cleavage furrow positioning. Early C. elegans embryos deficient in the cytokinetic regulator centralspindlin form furrows, due to an inhibitory activity that depends on aster positioning relative to the polar cortices. Here, we show polar relaxation is associated with depletion of cortical ECT-2, a RhoGEF, specifically at the posterior cortex. Asymmetric ECT-2 accumulation requires intact centrosomes, Aurora A (AIR-1), and myosin-dependent cortical flows. Within a localization competent ECT-2 fragment, we identified three putative phospho-acceptor sites in the PH domain of ECT-2 that render ECT-2 responsive to inhibition by AIR-1. During both polarization and cytokinesis, our results suggest that centrosomal AIR-1 breaks symmetry via ECT-2 phosphorylation; this local inhibition of ECT-2 is amplified by myosin-driven flows that generate regional ECT-2 asymmetry. Together, these mechanisms cooperate to induce polarized assembly of cortical myosin, contributing to both embryo polarization and cytokinesis.

cell biology↗

bioRxiv2020

Rho1 activation recapitulates early gastrulation events in the ventral, but not dorsal, epithelium of Drosophila embryos

Ventral furrow formation, the first step in Drosophila gastrulation, is a well-studied example of tissue morphogenesis. Rho1 is highly active in a subset of ventral cells and is required for this morphogenetic event. However, it is unclear whether spatially patterned Rho1 activity alone is sufficient to recapitulate all aspects of this morphogenetic event, including anisotropic apical constriction and coordinated cell movements. Here, using an optogenetic probe that rapidly and robustly activates Rho1 in Drosophila tissues, we show that Rho1 activity induces ectopic deformations in the dorsal and ventral epithelia of Drosophila embryos. These perturbations reveal substantial differences in how ventral and dorsal cells, both within and outside the zone of Rho1 activation, respond to spatially and temporally identical patterns of Rho1 activation. Our results demonstrate that an asymmetric zone of Rho1 activity is not sufficient to recapitulate ventral furrow formation and indicate that additional, ventral-specific factors contribute to the cell- and tissue-level behaviors that emerge during ventral furrow formation.

developmental biology↗

bioRxiv2019

Competition between kinesin-1 and myosin-V define Drosophila posterior determination

Local accumulation of oskar (osk) mRNA in the Drosophila oocyte determines the posterior pole of the future embryo. Two major cytoskeletal components, microtubules and actin filaments, together with a microtubule motor, kinesin-1, and an actin motor, myosin-V, are essential for osk mRNA posterior localization. In this study, we use Staufen, an RNA-binding protein that colocalizes with osk mRNA, as a proxy for posterior determination. We demonstrate that posterior localization of osk/Staufen is determined by competition between kinesin-1 and myosin-V. While kinesin-1 removes osk/Staufen from the cortex along microtubules, myosin-V anchors osk/Staufen at the cortex. Myosin-V wins over kinesin-1 at the posterior pole due to low microtubule density at this site, while kinesin-1 wins it at anterior and lateral positions because they have high density of cortically-anchored microtubules. As a result, posterior determinants are removed from the anterior and lateral cortex but retained at the posterior pole. Thus, posterior determination of Drosophila oocyte is defined by kinesin-myosin competition, whose outcome is primarily determined by cortical microtubule density.

cell biology↗

bioRxiv2018

PLK1 plays dual roles in centralspindlin regulation during cytokinesis

Cytokinesis starts in anaphase with the formation of an actomyosin-based contractile ring at the equatorial cortex, which is governed by the local activation of the small GTPase RhoA. Here we delineated the contributions of PLK1 and Aurora B to RhoA activation and cytokinesis initiation in human cells. Knock-down of PRC1, which disrupts the spindle midzone, revealed the existence of two pathways that can initiate cleavage furrow ingression. One pathway depends on a well-organized spindle midzone and PLK1, while the other depends on Aurora B activity and centralspindlin oligomerization at the equatorial cortex and can operate independently of PLK1. We further show that PLK1 inhibition sequesters centralspindlin onto the spindle midzone making it unavailable for Aurora B-dependent oligomerization at the equatorial cortex. We propose that PLK1 activity promotes the release of centralspindlin from the spindle midzone through inhibition of PRC1, allowing centralspindlin to function as a regulator of spindle midzone formation and as an activator of RhoA at the equatorial cortex.

cell biology↗

bioRxiv2017

Cell cycle entry triggers a switch between two modes of Cdc42 activation during yeast polarization

Cell polarization underlies many cellular and organismal functions. The GTPase Cdc42 orchestrates polarization in many contexts. In budding yeast, polarization is associated with a focus of Cdc42*GTP which is thought to self sustain by recruiting a complex containing Cla4, a Cdc42-binding effector, Bem1, a scaffold and Cdc24, a Cdc42 GEF. Using optogenetics, we probe yeast polarization and find that local recruitment of Cdc24 or Bem1 is sufficient to induce polarization by triggering self-sustaining Cdc42 activity. However, the response to these perturbations depends on the recruited molecule, the cell cycle stage, and existing polarization sites. Before cell cycle entry, recruitment of Cdc24, but not Bem1, induces a metastable pool of Cdc42 that is sustained by positive feedback. Upon Cdk1 activation, recruitment of either Cdc24 or Bem1 creates a stable site of polarization that induces budding and inhibits formation of competing sites. Local perturbations have therefore revealed unexpected features of polarity establishment.

cell biology↗

bioRxiv2017

Harnessing optogenetics to probe sub-cellular mechanics

The mechanics of the actin cytoskeleton regulates cell morphogenesis during essential physiological processes. While cellular contractility is known to be largely RhoA-dependent, the process by which localized biochemical signals are translated into cell-level responses is not well understood. Here we combine optogenetic control of RhoA in space and time, live cell imaging and traction force microscopy to investigate the dynamics of actomyosin-based force generation in adherent fibroblasts. Local activation of RhoA not only stimulates local recruitment of actin and myosin, but also leads to increased traction forces outside the activation region that rapidly propagate across the cell via stress fibers and drive actin flow towards the region of heightened RhoA. Surprisingly, the flow reverses direction when local RhoA activation stops. We identify zyxin as a regulator of stress fiber mechanics, as stress fibers are fluid-like without flow reversal in its absence. These experimental data are used to constrain a physical model, which demonstrates that stress fibers are elastic-like, even at time scales exceeding turnover of constituent proteins. Such molecular control of actin mechanics likely plays critical roles in regulation of morphogenic events.

biophysics↗