dictyNews

Electronic Edition

Volume 49, number 4

February 10, 2023



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Abstracts

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Effects of wounds in the cell membrane on cell division



Md Istiaq Obaidi Tanvir & Shigehiko Yumura





published in Scientific Reports

https://www.nature.com/articles/s41598-023-28339-z



Cells are consistently subjected to wounding by physical or chemical 

damages from the external environment. We previously showed that 

a local wound of the cell membrane modulates the polarity of cell 

migration and the wounded cells escape from the wound site in 

Dictyostelium. Here, we examined effects of wounds on dividing cells. 

When the cell membrane at the cleavage furrow during cytokinesis 

was locally wounded using laserporation, furrow constriction was 

significantly accelerated. Neither myosin II nor cortexillins 

contributed to the acceleration, because the acceleration was not 

hindered in mutant cells deficient in these proteins. When the cell 

membrane outside the furrow was wounded, the furrow constriction 

was not accelerated. Instead, the wounded-daughter half became 

smaller and the unwounded half became larger, resulting in an 

asymmetrical cell division. These phenomena occurred independently 

of wound repair. When cells in anaphase were wounded at the 

presumptive polar region, about 30% of the wounded cells changed 

the orientation of the division axis. From these observations, we 

concluded that dividing cells also escape from the wound site. The 

wound experiments on dividing cells also provide new insights into 

the mechanism of cytokinesis and cell polarity establishment.





Submitted by Shigehiko Yumura [[log in to unmask]]

_________________________________________________________





Dynamics of intracellular cGMP during chemotaxis in Dictyostelium 

cells



Shigehiko Yumura, Masaki Nakano, Aika Honda, Yuuki Hashimoto, 

and Tomo Kondo





published in J. Cell Sci.

https://journals.biologists.com/jcs/article-abstract/136/3/jcs260591/286882/

Dynamics-of-intracellular-cGMP-during-chemotaxis?redirectedFrom=fulltext



Cyclic guanosine 3',5'-monophosphate (cGMP) is a ubiquitous 

important second messenger involved in various physiological functions. 

Here, intracellular cGMP (cGMPi) was visualized in chemotactic 

Dictyostelium cells using the fluorescent probe, D-Green cGull. When 

wild-type cells were stimulated with a chemoattractant, fluorescence 

ransiently increased, but guanylate cyclase-null cells did not show a 

change in fluorescence, suggesting that D-Green cGull is a reliable 

indicator of cGMPi. In the aggregation stage, the responses of cGMPi 

propagated in a wave-like fashion from the aggregation center. The 

oscillation of the cGMPi wave was synchronized almost in phase with 

those of other second messengers, such as the intracellular cAMP and 

Ca2+. The phases of these waves preceded those of the oscillations of 

actomyosin and cell velocity, suggesting that these second messengers 

are upstream of the actomyosin and chemotactic migration. An acute 

increase in cGMPi concentration released from membrane-permeable 

caged cGMP induced a transient shuttle of myosin II between the 

cytosol and cell cortex, suggesting a direct link between cGMP 

signaling and myosin II dynamics.





Submitted by Shigehiko Yumura [[log in to unmask]]

_________________________________________________________





Convergence of Ras- and Rac-regulated formin pathways is pivotal 

for phagosome formation and particle uptake in Dictyostelium

 

Sarah Körber, Alexander Junemann, Christof Litschko, Moritz 

Winterhoff and Jan Faix

 

Institute for Biophysical Chemistry, Hannover Medical School, 

30625 Hannover, Germany

 



PNAS, in press

 

Macroendocytosis comprising phagocytosis and macropinocytosis 

are actin-driven processes regulated by small GTPases that depend 

on the dynamic reorganization of the membrane that protrudes 

and internalizes extracellular material by cup-shaped structures. 

To effectively capture, enwrap, and internalize their targets, these 

cups are arranged into a peripheral ring or ruffle of protruding 

actin sheets emerging from an actin-rich, non-protrusive zone at 

its base. Despite extensive knowledge of the mechanism driving 

actin assembly of the branched network at the protrusive cup edge, 

which is initiated by the actin-related protein (Arp) 2/3 complex 

downstream of Rac signaling, our understanding of actin assembly 

in the base is still incomplete. In the Dictyostelium model system, 

the Ras-regulated formin ForG was previously shown to specifically 

contribute to actin assembly at the cup base. Loss of ForG is 

associated with a strongly impaired macroendocytosis and a 50% 

reduction of F-actin content at the base of phagocytic cups, in 

turn indicating the presence of additional factors that specifically 

contribute to actin formation at the base. Here, we show that ForG 

synergizes with the Rac-regulated formin ForB to form the bulk of 

linear filaments at the cup base. Consistently, combined loss of both 

formins virtually abolishes cup formation and leads to severe defects 

of macroendocytosis, emphasizing the relevance of converging Ras- 

and Rac-regulated formin pathways in assembly of linear filaments 

in the cup base, which apparently provide mechanical support to 

the entire structure. Remarkably, we finally show that active ForB, 

unlike ForG, additionally drives phagosome rocketing to aid particle 

internalization.





Submitted by Jan Faix [[log in to unmask]]

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[End dictyNews, volume 49, number 4]