Dr. Elting Recent Publications

Abstract Image:

Abstract: Spirostomum is a unicellular ciliate capable of contracting to a quarter of its body length in less than five milliseconds. When measured as fractional shortening, this is an order of magnitude faster than motion powered by actomyosin. Myonemes, which are protein networks found near the cortex of many protists, are believed to power Spirostomum contraction. Fast contraction, slow elongation, and calcium-triggering are hallmarks of myoneme-based motion. The biochemical basis of this motion and the molecular mechanism that supports such fast speeds are not well understood. Previous work suggests that myoneme structures in some protists are rich in centrin and Sfi1 homologs, two proteins that may underlie contraction. Centrin undergoes a significant conformational change in the presence of calcium, allowing it to bind to other centrin molecules. To understand Spirostomum contraction, we measure changes in cortical structures and model contraction of the whole cell and of the underlying protein complexes. We provide evidence that centrin/Sfi1 structures are responsible for contraction, which we propose is powered by a modulated entropic spring. Using this model, we recapitulate organismal-scale contraction in mesh simulation experiments and demonstrate the importance of structural organization of myoneme in a fishnet-like structure. These results provide a cohesive, multiscale model for the contraction of Spirostomum. Deeper understanding of how single cells can execute extreme shape changes holds potential for advancing cell biophysics, synthetically engineering contractile machinery, and cellular-inspired engineering designs.

Abstract: In nature, several ciliated protists possess the remarkable ability to execute ultrafast motions using protein assemblies called myonemes, which contract in response to Ca2+ ions. Existing theories, such as actomyosin contractility and macroscopic biomechanical latches, do not adequately describe these systems, necessitating development of models to understand their mechanisms. In this study, we image and quantitatively analyze the contractile kinematics observed in two ciliated protists (Vorticella sp. and Spirostomum sp.), and, based on the mechanochemistry of these organisms, we propose a minimal mathematical model that reproduces our observations as well as those published previously. Analyzing the model reveals three distinct dynamic regimes, differentiated by the rate of chemical driving and the importance of inertia. We characterize their unique scaling behaviors and kinematic signatures. Besides providing insights into Ca2+- powered myoneme contraction in protists, our work may also inform the rational design of ultrafast bioengineered systems such as active synthetic cells.

Abstract: A recent study highlights the indispensability of the augmin complex for the construction of mitotic spindle bridging fibers, which in turn support accurate chromosome attachment and segregation.

 

Abstract: The fission yeast S. pombe divides via closed mitosis, meaning that spindle elongation and chromosome segregation transpire entirely within the complete nuclear envelope. Both the spindle and nuclear envelope must undergo significant conformation changes and exert varying forces on each other during this process. Previous work has demonstrated that nuclear envelope expansion and spindle pole body (SPB) embedding in the nuclear envelope are required for normal S. pombe mitosis, and mechanical modeling has described potential contributions of the spindle to nuclear morphology. However, it is not yet fully clear how and to what extent the nuclear envelope and mitotic spindle each directly shape each other during closed mitosis. Here, we investigate this relationship by observing the behaviors of spindles and nuclei in live mitotic fission yeast following laser ablation. First, we characterize these dynamics in molecularly typical S. pombe spindles, finding them to be stabilized by dense crosslinking, before demonstrating that the compressive force acting on the spindle poles is higher in mitotic cells with greater nuclear envelope tension and that spindle compression can be relieved by lessening nuclear envelope tension via laser ablation. Finally, we use a quantitative model to interpret how these data directly demonstrate that fission yeast spindles and nuclear envelopes are a mechanical pair that can each shape the other’s morphology.

Abstract: The mechanics that govern the constriction of the contractile ring remain poorly understood yet are critical to understanding the forces that drive cytokinesis. We used laser ablation in fission yeast cells to unravel these mechanics focusing on the role of Cdc15p as a putative anchoring protein. Our work shows that the severed constricting contractile ring recoils to a finite point leaving a gap that can heal if less than ∼1 µm. Severed contractile rings in Cdc15p-depleted cells exhibit an exaggerated recoil, which suggests that the recoil is limited by the anchoring of the ring to the plasma membrane. Based on a physical model of the severed contractile ring, we propose that Cdc15p impacts the stiffness of the contractile ring more than the viscous drag.