Coin Tossing Explains the Activity of Opposing Microtubule Motors on Phagosomes

Abstract

SummaryHow the opposing activity of kinesin and dynein motors generates polarized distribution of organelles inside cells is poorly understood and hotly debated [1, 2]. Possible explanations include stochastic mechanical competition [3, 4], coordinated regulation by motor-associated proteins [5, 6, 7], mechanical activation of motors [8], and lipid-induced organization [9]. Here, we address this question by using phagocytosed latex beads to generate early phagosomes (EPs) that move bidirectionally along microtubules (MTs) in an in vitro assay [9]. Dynein/kinesin activity on individual EPs is recorded as real-time force generation of the motors against an optical trap. Activity of one class of motors frequently coincides with, or is rapidly followed by opposite motors. This leads to frequent and rapid reversals of EPs in the trap. Remarkably, the choice between dynein and kinesin can be explained by the tossing of a coin. Opposing motors therefore appear to function stochastically and independently of each other, as also confirmed by observing no effect on kinesin function when dynein is inhibited on the EPs. A simple binomial probability calculation based on the geometry of EP-microtubule contact explains the observed activity of dynein and kinesin on phagosomes. This understanding of intracellular transport in terms of a hypothetical coin, if it holds true for other cargoes, provides a conceptual framework to explain the polarized localization of organelles inside cells.

Stochastic asymmetric repartition of lytic machinery in dividing CD8+ T cells generates heterogeneous killing behavior

“…Together, our results point out a mechanism of heterogeneity generation that is for the most part stochastic and might be a general mechanism for generating heterogeneity in dividing cells. The possibility that particulate material is unevenly distributed in telophase into two nascent daughter cells has been proposed for other organelles and in other cellular systems (Bergeland et al, 2001;Carlton et al, 2020;Sanghavi et al, 2018).…”

“…Together, our results point out a mechanism of heterogeneity generation that is for the most part stochastic and might be a general mechanism for generating heterogeneity in dividing cells. The possibility that particulate material is unevenly distributed in telophase into two nascent daughter cells has been proposed for other organelles and in other cellular systems ( Bergeland et al, 2001 ; Carlton et al, 2020 ; Sanghavi et al, 2018 ). Indeed, in MDCK cells, microscopy analysis and mathematical modeling based on the laws of probability suggested that endosome/lysosome partitioning between daughter cells is stochastic ( Bergeland et al, 2001 ).…”

Diffusion of kinesin motors on cargo can enhance binding and run lengths during intracellular transport

“…This work adds to a growing body of evidence that, first, the position of motors on the cargo (whether free or not) impacts transport [4,24]; second, that mobility on the cargo surface further influences transport [8,9,17,18,25]; and, third, that there are significant differences in the arrangement of motors on cargo in cells [3,18], for example via changes to lipid content [26,27]. The closest direct experimental study related to our work is by the Xu Lab [9].…”

Stochastic asymmetric repartition of lytic machinery in dividing CD8+T cells generates heterogeneous killing behavior

“…The possibility that particulate material is unevenly distributed in telophase into two nascent daughter cells has been proposed for other organelles and in other cellular systems (Bergeland et al, 2001; Carlton et al, 2020; Sanghavi et al, 2018). Indeed, in MDCK cells, microscopy analysis and mathematical modelling based on the laws of probability suggested that endosomes/lysosomes partitioning between daughter cells is stochastic (Bergeland et al, 2001).…”