Coupling of cytoplasm and adhesion dynamics determines cell polarization and locomotion

Observations of single epidermal cells on flat adhesive substrates have revealed two distinct morphological and functional states, namely a non-migrating symmetric unpolarized state and a migrating asymmetric polarized state. These states are characterized by different spatial distributions and dynamics of important biochemical cell components: F-actin and myosin-II form the contractile part of the cytoskeleton, and integrin receptors in the plasma membrane connect F-actin filaments to the substratum. In this way, focal adhesion complexes are assembled, which determine cytoskeletal force transduction and subsequent cell locomotion. So far, physical models have reduced this phenomenon either to gradients in regulatory control molecules or to different mechanics of the actin filament system in different regions of the cell. Here we offer an alternative and self-organizational model incorporating polymerization, pushing and sliding of filaments, as well as formation of adhesion sites and their force dependent kinetics. All these phenomena can be combined into a non-linearly coupled system of hyperbolic, parabolic and elliptic differential equations. Aim of this article is to show how relatively simple relations for the small-scale mechanics and kinetics of participating molecules may reproduce the emergent behavior of polarization and migration on the large-scale cell level.Comment: v2 (updates from proof): add TOC, clarify Fig. 4, fix several typo

Untersuchungen zur Adhäsionsdynamik migrierender Keratinozyten

Einzelzellen innerhalb eines Gewebes sind über vielfältige Verbindungsstrukturen miteinander verknüpft. Die mechanische Verbindung des Aktin-Zytoskeletts an die extrazelluläre Matrix wird über Proteinkomplexe ermöglicht, die abgegrenze Adhäsionsbereiche in der PLasmamembran bilden und als Fokaladhäsionen bezeichnet werden. Durch regulierte Bildung und Auflösung solcher Fokaladhäsionen können sich Gewebe reograniseren bzw. neu bilden, was beispielsweise in der Embryonalentwicklung oder bei Wundheilungsprozessen eine wichtige Rolle spielt. Vor allem in migrierenden Zellen sind Fokaladhäsionen sehr dynamische Strukturen, die innerhalb von Minuten auf und abgebaut werden können. Dabei unterliegen einzlene Proteine einem ständigen kinetischen Austausch, sodass sie teilweise nur wenige Sekunden im Adhäsionskomplex verweilen. In dieser Arbeit wurde die Regulation des Auf- und Abbaus von Fokaladhäsionen in migrierenden Keratinozyten mit verschiedenen quantitativen lichtmikroskopischen Methoden untersucht. Unter anderem wurde die Austauschdynamik des Fokaladhäsionsproteins Vinculin mit FRAP (Fluorescence Recovery After Photobleaching) gemessen.Dabei konnte gezeigt werden,dass Vinculin in der Fokaladhäsion im Laufe ihres Reifungsprozesses stabilisiert wird. Diese Stabiliserung wird durch die Dephosphorylierung von Vinculin an einem betimmten Tyrosinrest (TYR1065) reguliert und geht mit einer erhöhten Zugkraftübertragung der Fokaladhäsion einher. Kurz vor Auflösung der Fokaladhäsion kommt es wieder zur Destabilisierung von Vinculin. Auf Grundlage dieser Ergebnisse wurde die These aufgestellt, dass die Adhäsionsstärke der Zelle über die gezielte Regulation des Vinculinaustausches moduliert werden kann. Desweiteren wurde der Auf- und Abbau von Fokaladhäsionen im Zusammenhang mit der Dynamik des Aktin-Zytoskeletts und der Polarisierung der Zelle untersucht. Anhand der gewonnenen Ergebnisse wurde ein Modell konstruiert, nach dem die Struktur des Aktin-Zytoskeletts über die Bildung von Fokaladhäsionen organisiert wird

Molecular Remodeling of the Presynaptic Active Zone of Drosophila Photoreceptors via Activity-Dependent Feedback

SummaryNeural activity contributes to the regulation of the properties of synapses in sensory systems, allowing for adjustment to a changing environment. Little is known about how synaptic molecular components are regulated to achieve activity-dependent plasticity at central synapses. Here, we found that after prolonged exposure to natural ambient light the presynaptic active zone in Drosophila photoreceptors undergoes reversible remodeling, including loss of Bruchpilot, DLiprin-α, and DRBP, but not of DSyd-1 or Cacophony. The level of depolarization of the postsynaptic neurons is critical for the light-induced changes in active zone composition in the photoreceptors, indicating the existence of a feedback signal. In search of this signal, we have identified a crucial role of microtubule meshwork organization downstream of the divergent canonical Wnt pathway, potentially via Kinesin-3 Imac. These data reveal that active zone composition can be regulated in vivo and identify the underlying molecular machinery

Costamere protein expression and tissue composition of rotator cuff muscle after tendon release in sheep

Previous studies suggested that degradation of contractile tissue requires cleavage of the costamere, a structural protein complex that holds sarcomeres in place. This study examined if costamere turnover is affected by a rotator cuff tear in a previously established ovine model. We found the activity of focal adhesion kinase (FAK), a main regulator of costamere turnover, was unchanged at 2 weeks but decreased by 27% 16 weeks after surgical release of the infraspinatus tendon. This was accompanied by cleavage of the costamere protein talin into a 190 kDa fragment while full length talin remained unchanged. At 2 weeks after tendon release, muscle volume decreased by 17 cm from an initial 185 cm(3) , the fatty tissue volume was halved, and the contractile tissue volume remained unchanged. After 16 weeks, the muscle volume decreased by 36 cm(3) , contractile tissue was quantitatively lost, and the fat content increased by 184%. Nandrolone administration mitigated the loss of contractile tissue by 26% and prevented fat accumulation, alterations in FAK activity, and talin cleavage. Taken together, these findings imply that muscle remodeling after tendon release occurs in two stages. The early decrease of muscle volume is associated with reduction of fat; while, the second stage is characterized by substantial loss of contractile tissue accompanied by massive fat accumulation. Regulation of costamere turnover is associated with the loss of contractile tissue and seems to be impacted by nandrolone treatment. Clinically, the costamere may represent a potential intervention target to mitigate muscle loss after a rotator cuff tear. © 2017 The Authors. Journal of Orthopaedic Research published by Wiley Periodicals, Inc. on behalf of the Orthopaedic Research Society. J Orthop Res

Cytoplasmic poly-GA aggregates impair nuclear import of TDP-43 in C9orf72 ALS/FTLD

A repeat expansion in the non-coding region of C9orf72 gene is the most common mutation causing frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). Sense and antisense transcripts are translated into aggregating dipeptide repeat (DPR) proteins in all reading frames (poly-GA,-GP,-GR,-PA and -PR) through an unconventional mechanism. How these changes contribute to cytoplasmic mislocalization and aggregation of TDP-43 and thereby ultimately leading to neuron loss remains unclear. The repeat RNA itself and poly-GR/PR have been linked to impaired nucleocytoplasmic transport. Here, we show that compact cytoplasmic poly-GA aggregates impair nuclear import of a reporter containing the TDP-43 nuclear localization (NLS) signal. However, a reporter containing a non-classical PY-NLS was not affected. Moreover, poly-GA expression prevents TNF alpha induced nuclear translocation of p65 suggesting that poly-GA predominantly impairs theimportin-alpha/beta-dependent pathway. In neurons, prolonged poly-GA expression induces partial mislocalization of TDP-43 into cytoplasmic granules. Rerouting poly-GA to the nucleus prevented TDP-43 mislocalization, suggesting a cytoplasmic mechanism. In rescue experiments, expression of importin-alpha (KPNA3, KPNA4) or nucleoporins (NUP54, NUP62) restores the nuclear localization of the TDP reporter. Taken together, inhibition of nuclear import of TDP-43 by cytoplasmic poly-GA inclusions causally links the two main aggregating proteins in C9orf72 ALS/FTLD pathogenesis

Checkliste zur Unterstützung der Helmholtz-Zentren bei der Implementierung von Richtlinien für nachhaltige Forschungssoftware

Mit der voranschreitenden Digitalisierung von Forschung und Lehre steigt die Zahl an Software-Lösungen, die an wissenschaftlichen Einrichtungen entstehen und zur Erkenntnisgewinnung genutzt werden. Die – unter dem Stichwort Open Science geforderte – Zugänglichkeit und Nachnutzung von wissenschaftlichen Ergebnissen kann in vielen Fachgebieten nur sichergestellt werden, wenn neben Forschungsdaten auch Programmcode offen zugänglich gemacht wird. Die vorliegende Handreichung richtet sich an Entscheider*innen in den Helmholtz-Zentren, die sich mit der Implementierung von Richtlinien für nachhaltige Forschungssoftware befassen. Sie ergänzt eine Muster-Richtlinie, die den Zentren bereits eine richtungsweisende und nachnutzbare Vorlage zur Erstellung von Regelungen für einen nachhaltigen Umgang mit Forschungssoftware gibt

Cell Polarity: Focal Adhesion and Actin Dynamics in Migrating Cells

International audienceIn this chapter, we learn to identify image objects in time-lapse movies of single migrating cells. We analyze their shape, growth dynamics, and movement of the associated actin network, which is recorded in a separate channel. This way, we get familiar with optical flow analysis and learn how to integrate the information of different image data sources to discover relationships between different object features

Cell Polarity: Focal Adhesion and Actin Dynamics in Migrating Cells

International audienceIn this chapter, we learn to identify image objects in time-lapse movies of single migrating cells. We analyze their shape, growth dynamics, and movement of the associated actin network, which is recorded in a separate channel. This way, we get familiar with optical flow analysis and learn how to integrate the information of different image data sources to discover relationships between different object features