Microtubule detyrosination drives symmetry breaking to polarize cells for directed cell migration

Principles of organelle positioning in motile and non-motile cells

Cells are equipped with asymmetrically localised and functionally specialised components, including cytoskeletal structures and organelles. Positioning these components to specific intracellular locations in an asymmetric manner is critical for their functionality and affects processes like immune responses, tissue maintenance, muscle functionality, and neurobiology. Here, we provide an overview of strategies to actively move, position, and anchor organelles to specific locations. By conceptualizing the cytoskeletal forces and the organelle-to-cytoskeleton connectivity, we present a framework of active positioning of both membrane-enclosed and membrane-less organelles. Using this framework, we discuss how different principles of force generation and organelle anchorage are utilised by different cells, such as mesenchymal and amoeboid cells, and how the microenvironment influences the plasticity of organelle positioning. Given that motile cells face the challenge of coordinating the positioning of their content with cellular motion, we particularly focus on principles of organelle positioning during migration. In this context, we discuss novel findings on organelle positioning by anchorage-independent mechanisms and their advantages and disadvantages in motile as well as stationary cells.

The α-tubulin acetyltransferase ATAT1: structure, cellular functions, and its emerging role in human diseases

The acetylation of α-tubulin on lysine 40 is a well-studied post-translational modification which has been associated with the presence of long-lived stable microtubules that are more resistant to mechanical breakdown. The discovery of α-tubulin acetyltransferase 1 (ATAT1), the enzyme responsible for lysine 40 acetylation on α-tubulin in a wide range of species, including protists, nematodes, and mammals, dates to about a decade ago. However, the role of ATAT1 in different cellular activities and molecular pathways has been only recently disclosed. This review comprehensively summarizes the most recent knowledge on ATAT1 structure and substrate binding and analyses the involvement of ATAT1 in a variety of cellular processes such as cell motility, mitosis, cytoskeletal organization, and intracellular trafficking. Finally, the review highlights ATAT1 emerging roles in human diseases and discusses ATAT1 potential enzymatic and non-enzymatic roles and the current efforts in developing ATAT1 inhibitors.

Patterning of the cell cortex by Rho GTPases

The Rho GTPases - RHOA, RAC1 and CDC42 - are small GTP binding proteins that regulate basic biological processes such as cell locomotion, cell division and morphogenesis by promoting cytoskeleton-based changes in the cell cortex. This regulation results from active (GTP-bound) Rho GTPases stimulating target proteins that, in turn, promote actin assembly and myosin 2-based contraction to organize the cortex. This basic regulatory scheme, well supported by in vitro studies, led to the natural assumption that Rho GTPases function in vivo in an essentially linear matter, with a given process being initiated by GTPase activation and terminated by GTPase inactivation. However, a growing body of evidence based on live cell imaging, modelling and experimental manipulation indicates that Rho GTPase activation and inactivation are often tightly coupled in space and time via signalling circuits and networks based on positive and negative feedback. In this Review, we present and discuss this evidence, and we address one of the fundamental consequences of coupled activation and inactivation: the ability of the Rho GTPases to self-organize, that is, direct their own transition from states of low order to states of high order. We discuss how Rho GTPase self-organization results in the formation of diverse spatiotemporal cortical patterns such as static clusters, oscillatory pulses, travelling wave trains and ring-like waves. Finally, we discuss the advantages of Rho GTPase self-organization and pattern formation for cell function.

[Integrin and N-cadherin Co-Regulate the Polarity of Mesenchymal Stem Cells via Mechanobiological Mechanisms]

Objective

To investigate the synergistic regulation of the polarization of mesenchymal stem cells by integrin and N-cadherin-mediated mechanical adhesion and the underlying mechanobiological mechanisms.

Methods

Bilayer polyethylene glyeol (PEG) hydrogels were formulated and modified with RGD and HAVDI peptides, respectively, to achieve mechanical adhesion to integrin and N-cadherin and to replicate the integrin-mediated mechanical interaction between cells and the extracellular matrix and the N-cadherin-mediated cell-cell mechanical interaction. The polar proteins, phosphatidylinositol 3-kinase (PI3K) and phosphorylated myosin light chain (pMLC), were characterized through immunofluorescence staining in individual cells with or without contact with HAVDI peptides under integrin-mediated adhesion, N-cadherin-mediated adhesion, and different intracellular forces. Their expression levels and polar distribution were analyzed using Image J.

Results

Integrin-mediated adhesion induced significantly higher polar strengths of PI3K and pMLC in the contact group than in those in the no contact group, resulting in the concentration of the polar angle of PI3K to β-catenin in the range of 135° to 180° and the concentration of the polar angle of pMLC to β-catenin in the range of 0° to 45° in the contact group. Inhibition of integrin function led to inhibition of the polarity distribution of PI3K in the contact group, but did not change the polarity distribution of pMLC protein. The effect of N-cadherin on the polarity distributions of PI3K and pMLC was similar to that of integrin. However, inhibition of the mechanical adhesion of N-cadherin led to inhibition of the polarity intensity and polarity angle distribution of PI3K and pMLC proteins in the contact group. Furthermore, inhibition of the mechanical adhesion of N-cadherin caused weakened polarity intensity of integrin β1, reducing the proportion of cells with polarity angles between integrin β1 and β-catenin concentrating in the range of 135° to 180°. Additionally, intracellular forces influenced the polar distribution of PI3K and pMLC proteins. Reducing intracellular forces weakened the polarity intensity of PI3K and pMLC proteins and their polarity distribution, while increasing intracellular forces enhanced the polarity intensity of PI3K and pMLC proteins and their polarity distribution.

Conclusion

Integrin and N-cadherin co-regulate the polarity distribution of cell proteins and N-cadherin can play an important role in the polarity regulation of stem cells through local inhibition of integrin.

Microtubule control of migration: Coordination in confinement

The microtubule cytoskeleton has a well-established, instrumental role in coordinating cell migration. Decades of research has focused on understanding how microtubules couple intracellular trafficking with cortical targeting and spatial organization of signaling to facilitate locomotion. Movement in physically challenging environments requires coordination of forces generated by the actin cytoskeleton to drive cell shape changes, with microtubules acting to spatially regulate contractility. Recent work has demonstrated that the mechanical properties of microtubules are adaptive to stress, leading to a new understanding of their roles in cell migration. Herein we review new developments in how microtubules sense and adapt to changes in the physical properties of their environment during migration. We frame our discussion around our current understanding of how microtubules target cell-matrix adhesions, and their role in the spatiotemporal coordination of signaling to form mechano feedback loops. We expand on how these mechanisms may influence cell morphology in confined three-dimensional settings, and the importance of locally tuning the mechanical stability of polymers in response to mechanical cues. Finally, we discuss new roles for Golgi-derived microtubules in mechanosensing, and how preferential motor use may influence polymer stability to resist the physical constraints cells experience in confined environments.

The Role of MAPRE2 and Microtubules in Maintaining Normal Ventricular Conduction

BACKGROUND

Brugada syndrome is associated with loss-of-function SCN5A variants, yet these account for only ≈20% of cases. A recent genome-wide association study identified a novel locus within MAPRE2, which encodes EB2 (microtubule end-binding protein 2), implicating microtubule involvement in Brugada syndrome.

METHODS

A mapre2 knockout zebrafish model was generated using CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat-associated protein 9) and validated by Western blot. Larval hearts at 5 days post-fertilization were isolated for voltage mapping and immunocytochemistry. Adult fish hearts were used for ECG, patch clamping, and immunocytochemistry. Morpholinos were injected into embryos at 1-cell stage for knockdown experiments. A transgenic zebrafish line with cdh2 tandem fluorescent timer was used to study adherens junctions. Microtubule plus-end tracking and patch clamping were performed in human induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) with MAPRE2 knockdown and knockout, respectively.

RESULTS

Voltage mapping of mapre2 knockout hearts showed a decrease in ventricular maximum upstroke velocity of the action potential and conduction velocity, suggesting loss of cardiac voltage-gated sodium channel function. ECG showed QRS prolongation in adult knockout fish, and patch clamping showed decreased sodium current density in knockout ventricular myocytes and arrhythmias in knockout iPSC-CMs. Confocal imaging showed disorganized adherens junctions and mislocalization of mature Ncad (N-cadherin) with mapre2 loss of function, associated with a decrease of detyrosinated tubulin. MAPRE2 knockdown in iPSC-CMs led to an increase in microtubule growth velocity and distance, indicating changes in microtubule dynamics. Finally, knockdown of ttl encoding tubulin tyrosine ligase in mapre2 knockout larvae rescued tubulin detyrosination and ventricular maximum upstroke velocity of the action potential.

CONCLUSIONS

Genetic ablation of mapre2 led to a decrease in voltage-gated sodium channel function, a hallmark of Brugada syndrome, associated with disruption of adherens junctions, decrease of detyrosinated tubulin as a marker of microtubule stability, and changes in microtubule dynamics. Restoration of the detyrosinated tubulin fraction with ttl knockdown led to rescue of voltage-gated sodium channel-related functional parameters in mapre2 knockout hearts. Taken together, our study implicates microtubule dynamics in the modulation of ventricular conduction.

Advances in Regulating Cellular Behavior Using Micropatterns

Micropatterns, characterized as distinct physical microstructures or chemical adhesion matrices on substance surfaces, have emerged as a powerful tool for manipulating cellular activity. By creating specific extracellular matrix microenvironments, micropatterns can influence various cell behaviors, including orientation, proliferation, migration, and differentiation. This review provides a comprehensive overview of the latest advancements in the use of micropatterns for cell behavior regulation. It discusses the influence of micropattern morphology and coating on cell behavior and the underlying mechanisms. It also highlights future research directions in this field, aiming to inspire new investigations in materials medicine, regenerative medicine, and tissue engineering. The review underscores the potential of micropatterns as a novel approach for controlling cell behavior, which could pave the way for breakthroughs in various biomedical applications.