scholarly journals In vivo Interactions between Myosin XI, Vesicles, and Filamentous Actin Are Fast and Transient

2019 ◽  
Author(s):  
Jeffrey P. Bibeau ◽  
Fabienne Furt ◽  
S. Iman Mousavi ◽  
James L. Kingsley ◽  
Max F. Levine ◽  
...  
Keyword(s):  
Membrane Trafficking ◽  
Physcomitrella Patens ◽  
Epifluorescence Microscopy ◽  
Markov Modeling ◽  
Filamentous Actin ◽  
Hidden Markov Modeling ◽  
Short Run ◽  
Myosin Xi ◽  
Run Lengths

AbstractThe apical actin cytoskeleton and active membrane trafficking machinery are essential in driving polarized cell growth. To better understand the interactions between myosin XI, vesicles, and actin filament in vivo, we performed Fluorescence Recovery After Photobleaching (FRAP) and showed that the dynamics of myosin XIa at the tip are actin-dependent and that approximately half of myosin XI is bound to vesicles in the cell. To obtain single particle information, we used Variable Angle Epifluorescence Microscopy (VAEM) in Physcomitrella patens protoplasts to demonstrate that myosin XIa and VAMP72-labeled vesicles localize in time and space for periods lasting only a few seconds. Using tracking data with Hidden Markov Modeling (HMM), we showed that myosin XIa and VAMP72-labeled vesicles exhibit short runs of actin-dependent directed transport. We also found that the interaction of myosin XI with vesicles is short lived. Together, this bound fraction, fast off-rate, and short run lengths are expected to be critical for the dynamic oscillations observed at the cell apex, and may be vital for the regulation and recycling of the exocytosis machinery; while simultaneously promoting the vesicle focusing and secretion at the tip, necessary for cell wall expansion.

scholarly journals In vivo interactions between myosin XI, vesicles and filamentous actin are fast and transient in Physcomitrella patens

2020 ◽  
Vol 133 (4) ◽  
pp. jcs234682 ◽  
Author(s):  
Jeffrey P. Bibeau ◽  
Fabienne Furt ◽  
S. Iman Mousavi ◽  
James L. Kingsley ◽  
Max F. Levine ◽  
...  
Keyword(s):  
Physcomitrella Patens ◽  
Filamentous Actin ◽  
Myosin Xi

Deriving Effective Decision-Making Strategies of Prosthetists: Using Hidden Markov Modeling and Qualitative Analysis to Compare Experts and Novices

2021 ◽  
pp. 001872082110328
Author(s):  
Pratima Saravanan ◽  
Jessica Menold
Keyword(s):  
Decision Making ◽  
Qualitative Analysis ◽  
Clinical Decision Making ◽  
Hidden Markov ◽  
Activity Level ◽  
Markov Modeling ◽  
Support Tool ◽  
Case Complexity ◽  
Hidden Markov Modeling ◽  
Expert And Novice

Objective This research focuses on studying the clinical decision-making strategies of expert and novice prosthetists for different case complexities. Background With an increasing global amputee population, there is an urgent need for improved amputee care. However, current prosthetic prescription standards are based on subjective expertise, making the process challenging for novices, specifically during complex patient cases. Hence, there is a need for studying the decision-making strategies of prosthetists. Method An interactive web-based survey was developed with two case studies of varying complexities. Navigation between survey pages and time spent were recorded for 28 participants including experts ( n = 20) and novices ( n = 8). Using these data, decision-making strategies, or patterns of decisions, during prosthetic prescription were derived using hidden Markov modeling. A qualitative analysis of participants’ rationale regarding decisions was used to add a deep contextualized understanding of decision-making strategies derived from the quantitative analysis. Results Unique decision-making strategies were observed across expert and novice participants. Experts tended to focus on the personal details, activity level, and state of the residual limb prior to prescription, and this strategy was independent of case complexity. Novices tended to change strategies dependent upon case complexity, fixating on certain factors when case complexity was high. Conclusion The decision-making strategies of experts stayed the same across the two cases, whereas the novices exhibited mixed strategies. Application By modeling the decision-making strategies of experts and novices, this study builds a foundation for development of an automated decision-support tool for prosthetic prescription, advancing novice training, and amputee care.

scholarly journals Robust polarity establishment occurs via an endocytosis-based cortical corralling mechanism

2013 ◽  
Vol 200 (4) ◽  
pp. 407-418 ◽  
Author(s):  
Mini Jose ◽  
Sylvain Tollis ◽  
Deepak Nair ◽  
Jean-Baptiste Sibarita ◽  
Derek McCusker
Keyword(s):  
High Resolution ◽  
Membrane Trafficking ◽  
In Vivo Studies ◽  
Biological Processes ◽  
Constant Frequency ◽  
In Silico Modeling ◽  
Resolution Imaging ◽  
Polarity Establishment ◽  
Endocytic Vesicles

Formation of a stable polarity axis underlies numerous biological processes. Here, using high-resolution imaging and complementary mathematical modeling we find that cell polarity can be established via the spatial coordination of opposing membrane trafficking activities: endocytosis and exocytosis. During polarity establishment in budding yeast, these antagonistic processes become apposed. Endocytic vesicles corral a central exocytic zone, tightening it to a vertex that establishes the polarity axis for the ensuing cell cycle. Concomitantly, the endocytic system reaches an equilibrium where internalization events occur at a constant frequency. Endocytic mutants that failed to initiate periodic internalization events within the corral displayed wide, unstable polarity axes. These results, predicted by in silico modeling and verified by high resolution in vivo studies, identify a requirement for endocytic corralling during robust polarity establishment.

The functions of Reelin in membrane trafficking and cytoskeletal dynamics: implications for neuronal migration, polarization and differentiation

2017 ◽  
Vol 474 (18) ◽  
pp. 3137-3165 ◽  
Author(s):  
Jessica Santana ◽  
María-Paz Marzolo
Keyword(s):  
Membrane Trafficking ◽  
Neuronal Migration ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Signaling Cascade ◽  
Low Density ◽  
Lipoprotein Receptor ◽  
Density Lipoprotein Receptor ◽  
Reelin Signaling

Reelin is a large extracellular matrix protein with relevant roles in mammalian central nervous system including neurogenesis, neuronal polarization and migration during development; and synaptic plasticity with its implications in learning and memory, in the adult. Dysfunctions in reelin signaling are associated with brain lamination defects such as lissencephaly, but also with neuropsychiatric diseases like autism, schizophrenia and depression as well with neurodegeneration. Reelin signaling involves a core pathway that activates upon reelin binding to its receptors, particularly ApoER2 (apolipoprotein E receptor 2)/LRP8 (low-density lipoprotein receptor-related protein 8) and very low-density lipoprotein receptor, followed by Src/Fyn-mediated phosphorylation of the adaptor protein Dab1 (Disabled-1). Phosphorylated Dab1 (pDab1) is a hub in the signaling cascade, from which several other downstream pathways diverge reflecting the different roles of reelin. Many of these pathways affect the dynamics of the actin and microtubular cytoskeleton, as well as membrane trafficking through the regulation of the activity of small GTPases, including the Rho and Rap families and molecules involved in cell polarity. The complexity of reelin functions is reflected by the fact that, even now, the precise mode of action of this signaling cascade in vivo at the cellular and molecular levels remains unclear. This review addresses and discusses in detail the participation of reelin in the processes underlying neurogenesis, neuronal migration in the cerebral cortex and the hippocampus; and the polarization, differentiation and maturation processes that neurons experiment in order to be functional in the adult brain. In vivo and in vitro evidence is presented in order to facilitate a better understanding of this fascinating system.

scholarly journals Cleavage activates Dispatched for Sonic Hedgehog ligand release

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Daniel P Stewart ◽  
Suresh Marada ◽  
William J Bodeen ◽  
Ashley Truong ◽  
Sadie Miki Sakurada ◽  
...  
Keyword(s):  
Sonic Hedgehog ◽  
Membrane Trafficking ◽  
Developmental Disorders ◽  
Transmembrane Protein ◽  
Regulatory Mechanisms ◽  
Extracellular Loop ◽  
Site Mutation ◽  
Evolutionarily Conserved ◽  
Processing Site

Hedgehog ligands activate an evolutionarily conserved signaling pathway that provides instructional cues during tissue morphogenesis, and when corrupted, contributes to developmental disorders and cancer. The transmembrane protein Dispatched is an essential component of the machinery that deploys Hedgehog family ligands from producing cells, and is absolutely required for signaling to long-range targets. Despite this crucial role, regulatory mechanisms controlling Dispatched activity remain largely undefined. Herein, we reveal vertebrate Dispatched is activated by proprotein convertase-mediated cleavage at a conserved processing site in its first extracellular loop. Dispatched processing occurs at the cell surface to instruct its membrane re-localization in polarized epithelial cells. Cleavage site mutation alters Dispatched membrane trafficking and reduces ligand release, leading to compromised pathway activity in vivo. As such, convertase-mediated cleavage is required for Dispatched maturation and functional competency in Hedgehog ligand-producing cells.

scholarly journals CYK-4 regulates Rac, but not Rho, during cytokinesis

2017 ◽  
Vol 28 (9) ◽  
pp. 1258-1270 ◽  
Author(s):  
Yelena Zhuravlev ◽  
Sophia M. Hirsch ◽  
Shawn N. Jordan ◽  
Julien Dumont ◽  
Mimi Shirasu-Hiza ◽  
...  
Keyword(s):  
Alternative Model ◽  
Single Cell Analysis ◽  
Myosin Ii ◽  
Small Gtpases ◽  
Nucleotide Exchange ◽  
Filamentous Actin ◽  
Contractile Ring ◽  
Division Plane ◽  
Ring Constriction

Cytokinesis is driven by constriction of an actomyosin contractile ring that is controlled by Rho-family small GTPases. Rho, activated by the guanine-nucleotide exchange factor ECT-2, is upstream of both myosin-II activation and diaphanous formin-mediated filamentous actin (f-actin) assembly, which drive ring constriction. The role for Rac and its regulators is more controversial, but, based on the finding that Rac inactivation can rescue cytokinesis failure when the GTPase-activating protein (GAP) CYK-4 is disrupted, Rac activity was proposed to be inhibitory to contractile ring constriction and thus specifically inactivated by CYK-4 at the division plane. An alternative model proposes that Rac inactivation generally rescues cytokinesis failure by reducing cortical tension, thus making it easier for the cell to divide when ring constriction is compromised. In this alternative model, CYK-4 was instead proposed to activate Rho by binding ECT-2. Using a combination of time-lapse in vivo single-cell analysis and Caenorhabditis elegans genetics, our evidence does not support this alternative model. First, we found that Rac disruption does not generally rescue cytokinesis failure: inhibition of Rac specifically rescues cytokinesis failure due to disruption of CYK-4 or ECT-2 but does not rescue cytokinesis failure due to disruption of two other contractile ring components, the Rho effectors diaphanous formin and myosin-II. Second, if CYK-4 regulates cytokinesis through Rho rather than Rac, then CYK-4 inhibition should decrease levels of downstream targets of Rho. Inconsistent with this, we found no change in the levels of f-actin or myosin-II at the division plane when CYK-4 GAP activity was reduced, suggesting that CYK-4 is not upstream of ECT-2/Rho activation. Instead, we found that the rescue of cytokinesis in CYK-4 mutants by Rac inactivation was Cdc42 dependent. Together our data suggest that CYK-4 GAP activity opposes Rac (and perhaps Cdc42) during cytokinesis.

Decision-Feedback Stages Revealed by Hidden Markov Modeling of EEG

2021 ◽  
pp. 2150031
Author(s):  
Qin Tao ◽  
Yajing Si ◽  
Fali Li ◽  
Peiyang Li ◽  
Yuqin Li ◽  
...  
Keyword(s):  
Frontal Lobe ◽  
Visual Information ◽  
Hidden Markov ◽  
Decision Feedback ◽  
Markov Modeling ◽  
Feedback Process ◽  
Feedback Systems ◽  
Left Frontal Lobe ◽  
Hidden Markov Modeling ◽  
Independent Decision

Decision response and feedback in gambling are interrelated. Different decisions lead to different ranges of feedback, which in turn influences subsequent decisions. However, the mechanism underlying the continuous decision-feedback process is still left unveiled. To fulfill this gap, we applied the hidden Markov model (HMM) to the gambling electroencephalogram (EEG) data to characterize the dynamics of this process. Furthermore, we explored the differences between distinct decision responses (i.e. choose large or small bets) or distinct feedback (i.e. win or loss outcomes) in corresponding phases. We demonstrated that the processing stages in decision-feedback process including strategy adjustment and visual information processing can be characterized by distinct brain networks. Moreover, time-varying networks showed, after decision response, large bet recruited more resources from right frontal and right center cortices while small bet was more related to the activation of the left frontal lobe. Concerning feedback, networks of win feedback showed a strong right frontal and right center pattern, while an information flow originating from the left frontal lobe to the middle frontal lobe was observed in loss feedback. Taken together, these findings shed light on general principles of natural decision-feedback and may contribute to the design of biologically inspired, participant-independent decision-feedback systems.

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