Biology subjects

Guest, S. L.

Publications and source records attributed to Guest, S. L..

3 recordsLinked to original sources

bioRxiv2025

The Rhizarian amoeba Filoreta ramosa develops a neuron-like arborized network using conserved cytoskeletal mechanisms

The eukaryotic cytoskeleton generates remarkable diversity in cellular architecture despite being built from deeply conserved actin and tubulin polymers. Diversification of cytoskeletal regulators, motors, and filament-organizing proteins produces highly varied cellular morphologies across eukaryotes, yet certain higher-order architectures repeatedly emerge in distantly related lineages. One notable example is cytoskeletal arborization, which occurs not only in metazoan neurons but also in amoeboid lineages distributed throughout the eukaryotic tree. Whether these similar branched architectures arise through conserved cytoskeletal organization, independent reuse of shared molecular systems, or convergence driven by common physical constraints remains unresolved. Here, we investigate the rhizarian amoeba Filoreta ramosa, which forms a multinucleate reticulated network through branching and anastomosis. Using live imaging, immunofluorescence, morphometric analyses, and cytoskeletal drugs, we define how actin and microtubule systems organize branch formation, intracellular transport, and large-scale network architecture. Actin-rich protrusions initiate exploratory branchlets that become selectively stabilized through microtubule incorporation. Longitudinal microtubule arrays reinforce mature branches and support rapid bidirectional organelle transport, while branch nodes function as distributed sites of microtubule nucleation. These cytoskeletal features parallel key mechanisms underlying neuronal arborization, including actin-driven exploration, microtubule-dependent branch stabilization, and transport systems that scale with increasingly extended cytoskeletal networks. However, unlike neurons, Filoreta develops a decentralized reticulated network through repeated anastomosis and distributed microtubule organization, demonstrating that similar arborized morphologies can emerge through distinct architectural strategies. Our findings indicate that arborization can arise through multiple evolutionary adaptations to common cellular constraints. Shared cytoskeletal mechanisms repeatedly support branching architectures, but distinct topologies and modes of cellular organization demonstrate that evolution can reach arborization through different routes. Similar cytoskeletal networks may repeatedly emerge in diverse lineages when cells face the challenges of exploration, stabilization, and transport across increasingly larger scales. Filoreta therefore provides an experimentally tractable model for investigating how conserved cytoskeletal systems generate diverse arborized cellular architectures across eukaryotic evolution.

cell biology↗

bioRxiv2025

Myosin 2 drives actin contractility in fast-crawling species outside of the amorphean lineage

Myosin 2-dependent actin contractility drives essential cell functions including fast crawling motility in animal cells, Dictyostelium amoebae, and other species from the Amorphea lineage. Whether and how species outside this single eukaryotic group can generate contractile actin networks has been largely unexplored. We demonstrate that Naegleria, an amoeba from the Heterolobosea--an evolutionarily distant eukaryotic lineage that includes the fastest known crawling eukaryotes--expresses three distinct Myosin 2 homologs. Using biochemical assays and immunofluorescence, we show that these Myosin 2 proteins bind cellular actin networks and that these networks generate ATP-dependent contractility. By identifying additional Myosin 2 homologs in dozens of additional heterolobosean amoebae (but not obligate flagellates), we find a widespread correlation within this group between crawling behavior and contractile actin networks. This correlation includes the amoeba Vahlkampfia avara, which we demonstrate can crawl at speeds exceeding 180 m/min and has contractile actin networks and Myosin 2 homologs. These findings show that Myosin 2-driven contractility exists beyond Amorphea and is associated with diverse, fast-crawling cell types. Expanding the taxonomic breadth of actin network contractility impacts our basic understanding of cell motility, evolutionary biology, and of the fundamental biology of human pathogens that rely on fast cell migration.

cell biology↗

bioRxiv2023

Dynamic ventral disc contraction is necessary for Giardia attachment and host pathology

Giardia lamblia is a common parasitic protist that infects the small intestine and causes giardiasis, resulting in diarrhea, vomiting, weight loss, and malabsorption. Giardiasis leads to cellular damage, including loss of microvilli, disruption of tight junctions, impaired barrier function, enzyme inhibition, malabsorption, and apoptosis. In the host, motile Giardia trophozoites attach to the duodenal microvilli using a unique microtubule organelle called the ventral disc. Despite early observations of disc-shaped depressions in microvilli after parasite detachment, little is known about disc-mediated attachment mechanisms and there little direct evidence showing that parasite attachment causes cellular damage. However, advancements in in vitro organoid models of infection and genetic tools have opened new possibilities for studying molecular mechanisms of attachment and the impact of attachment on the host. Through high-resolution live imaging and a novel disc mutant, we provide direct evidence for disc contraction during attachment, resolving the long-standing controversy of its existence. Specifically, we identify three types of disc movements that characterize contraction, which in combination result in a decrease in disc diameter and volume. Additionally, we investigate the consequences of attachment and disc contractility using an attachment mutant that has abnormal disc architecture. In a human organoid model, we demonstrate that this mutant has a limited ability to break down the epithelial barrier as compared to wild type. Based on this direct evidence, we propose a model of attachment that incorporates disc contraction to generates the forces required for the observed "grasping" of trophozoites on the host epithelium. Overall, this work highlights the importance of disc contractility in establishing and maintaining parasite attachment, leading to intestinal barrier breakdown.

microbiology↗