Biology subjects

Tong, C. S.

Publications and source records attributed to Tong, C. S..

4 recordsLinked to original sources

bioRxiv2025

STIM1 and Endoplasmic Reticulum-Plasma Membrane Contact Sites Oscillate Independently of Calcium-Induced Calcium Release

Calcium (Ca{superscript 2}) release from intracellular stores, Ca{superscript 2} entry across the plasma membrane, and their coordination via store-operated Ca{superscript 2} entry (SOCE) are critical for receptor-activated Ca{superscript 2} oscillations. However, the precise mechanism of Ca{superscript 2} oscillations and whether their control loop resides at the plasma membrane or intracellularly remain unresolved. By examining the dynamics of stromal interaction molecule 1 (STIM1)--an endoplasmic reticulum (ER)-localized Ca{superscript 2} sensor that activates the Orai1 channel on the plasma membrane for SOCE--and in mast cells, we found that a significant proportion of cells exhibited STIM1 oscillations with the same periodicity as Ca{superscript 2} oscillations. These cortical oscillations, occurring in the cells cortical region and shared with ER-plasma membrane (ER-PM) contact sites proteins, were only detectable using total internal reflection fluorescence microscopy (TIRFM). Notably, STIM1 oscillations could occur independently of Ca{superscript 2} oscillations. Simultaneous imaging of cytoplasmic Ca{superscript 2} and ER Ca{superscript 2} with SEPIA-ER revealed that receptor activation does not deplete ER Ca{superscript 2}, whereas receptor activation without extracellular Ca{superscript 2} influx induces cyclic ER Ca{superscript 2} depletion. However, under such nonphysiological conditions, cyclic ER Ca{superscript 2} oscillations lead to sustained STIM1 recruitment, indicating that oscillatory Ca{superscript 2} release is neither necessary nor sufficient for STIM1 oscillations. Using optogenetic tools to manipulate ER-PM contact site dynamics, we found that persistent ER-PM contact sites reduced the amplitude of Ca{superscript 2} oscillations without alteration of oscillation frequency. Together, these findings suggest an active cortical mechanism governs the rapid dissociation of ER-PM contact sites, thereby control amplitude of oscillatory Ca{superscript 2} dynamics during receptor-induced Ca{superscript 2} oscillations.

cell biology↗

bioRxiv2023

Competition and Synergy of Arp2/3 and Formins in Nucleating Actin Waves

The assembly and disassembly of actin filaments and their regulatory proteins are crucial for maintaining cell structure or changing physiological state. However, because of the tremendous global impact of actin on diverse cellular processes, dissecting the specific role of actin regulatory proteins remains challenging. In this study, we employ actin waves that propagate on the cortex of mast cell to investigate the interplay between formins and the Arp2/3 complex in the nucleating and turnover of cortical actin. Our findings reveal that the recruitment of FMNL1 and mDia3 precedes the Arp2/3 complex in cortical actin waves. Membrane and GTPase-interaction can drive oscillations of FMNL1 in an actin-dependent manner, but active Cdc42 waves or constitutively-active FMNL1 mutant can form without actin waves. In addition to the apparent coordinated assembly of formins and Arp2/3, we further reveal their antagonism, where inhibition of Arp2/3 complex by CK-666 led to a transient increase in the recruitment of formins and actin polymerization. Our analysis suggest that the antagonism could not be explained for the competition between FMNL1 and Arp2/3 for monomeric actin. Rather, it is regulated by a limited pool of their common upstream regulator, Cdc42, whose level is negatively regulated by Arp2/3. Collectively, our study highlights the multifaceted interactions, cooperative or competitive, between formins and Arp2/3 complex, in the intricate and dynamic control of actin cytoskeletal network.

cell biology↗

bioRxiv2023

Collective dynamics of formin and microtubule and its crosstalk mediated by FHDC1

The coordination between actin and microtubule network is crucial, yet our understanding of the underlying mechanisms remains limited. In this study, we used travelling waves in the cell cortex to characterize the collective dynamics of cytoskeletal networks. Our findings show that Cdc42 and F-BAR-dependent actin waves in mast cells are mainly driven by formin-mediated actin polymerization, with the microtubule-binding formin FH2 domain-containing protein 1 (FHDC1) identified as an early regulator. The depolymerization of microtubules coincides with the nucleation of actin waves, and the concurrent release of FHDC1 from microtubule is required for actin waves. Lastly, we show the importance of the actin-microtubule linkage mediated by FHDC1 in crucial cellular processes such as cell division and migration. Our data provided molecular insights into the nucleation mechanisms of actin waves and uncover an antagonistic interplay between microtubule and actin polymerization in their collective dynamics.

cell biology↗

bioRxiv2023

Periodicity, Mixed-Mode Oscillations, and Multiple Timescale in a Phosphoinositide-Rho GTPase Network

While rhythmic contractile behavior is prevalent on the cortex of living cells, current experimental observation and mechanistic understanding primarily tackle a small subset of dynamical behavior including excitable or periodic events that can be described by simple activator-delayed inhibitor mechanisms. In this work we found that the oscillatory activation of Rho GTPase in nocodazole-treated mitotic rat basophilic leukemia (RBL) cells exhibited both simple and complex mixed-mode oscillations, with periodicity ranging from 30 sec to 5 min. Complex mixed-mode oscillations require at least two instability-generating mechanisms. We show that Rho oscillations at the fast timescale (20-30 sec) is regulated by phosphatidylinositol (3,4,5)-trisphosphate (PIP3) via an activator-delayed inhibitor mechanism, while the period of the slow reaction (minutes) is regulated by phosphatidylinositol 4-phosphate (PI(4)P) via an activator-substrate depletion mechanism where replenishment of phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2) is rate-limiting. Conversion from simple to complex oscillations could be induced by modulating PIP3 metabolism or membrane contact site dynamics. In particular, a period-doubling intermediate can be captured by PTEN depletion. Both period doubling and mixed-mode oscillations are intermediate states towards chaos. Collectively, these results suggest that phosphoinositide-Rho GTPase signaling network is poised at the edge of chaos and small parameter changes in the phosphoinositide metabolism network could confer cells the flexibility to rapidly transit into a number of ordered states with different periodicities.

cell biology↗