Membrane Tension Gates ERK-Mediated Regulation of Pluripotent Cell Fate

Cell fate transitions are frequently accompanied by changes in cell shape and mechanics. However, how cellular mechanics affects the instructive signaling pathways controlling cell fate is poorly understood. To probe the interplay between shape, mechanics, and fate, we use mouse embryonic stem cells (ESCs), which change shape as they undergo early differentiation. We find that shape change is regulated by a b-cateninmediated decrease in RhoA activity and subsequent decrease in the plasma membrane tension. Strikingly, preventing a decrease in membrane tension results in early differentiation defects in ESCs and gastruloids. Decreased membrane tension facilitates the endocytosis of FGF signaling components, which activate ERK signaling and direct the exit from the ESC state. Increasing Rab5a-facilitated endocytosis rescues defective early differentiation. Thus, we show that a mechanically triggered increase in endocytosis regulates early differentiation. Our findings are of fundamental importance for understanding how cell mechanics regulates biochemical signaling and therefore cell fate

Fluctuation-Based Super-Resolution Traction Force Microscopy

Cellular mechanics play a crucial role in tissue homeostasis and are often misregulated in disease. Traction force microscopy is one of the key methods that has enabled researchers to study fundamental aspects of mechanobiology; however, traction force microscopy is limited by poor resolution. Here, we propose a simplified protocol and imaging strategy that enhances the output of traction force microscopy by increasing i) achievable bead density and ii) the accuracy of bead tracking. Our approach relies on super-resolution microscopy, enabled by fluorescence fluctuation analysis. Our pipeline can be used on spinning-disk confocal or widefield microscopes and is compatible with available analysis software. In addition, we demonstrate that our workflow can be used to gain biologically relevant information and is suitable for fast long-term live measurement of traction forces even in light-sensitive cells. Finally, using fluctuation-based traction force microscopy, we observe that filopodia align to the force field generated by focal adhesions

A Picture of the Research Field of Doctoral Education from the Students’ Perspectives : Studies Using Questionnaires and Scales

Peer reviewe

PHOTOELECTRIC EFFECTS IN HIGH-RESISTIVITY EuSe

On a étudié les propriétés des monocristaux d'EuSe rouge transparent de haute résistivité au moyen de la photoconductivité et de la tension de photodiffusion avec des photons d'energie plus basse ou égale à celle-ci de la bande interdite Eg. Les pointes principales des spectres obtenus par la phoconductiuité ou photovoltaïque se trouvent à l'énergie de 1,85 eV équivalente à Eg dans EuSe. On a trouvé deux niveaux de défaut aux énergies 1,3 eV et 1,67 eV respectivement.The properties of red- transparent high-resistivity EuSe single crystals have been studied by means of the photoconductivity and photodiffusive voltage with photon energies less or equal to the forbidden energy gap Eg. In both the photoconduction and photovoltage spectra the main peak is situated at a photon energy of 1.85 eV corresponding to Eg in EuSe. Two defect levels were found at photon energies 1.3 and 1.67 eV

High frequency alternating current light-emitting diodes using Langmuir-Blodgett films

Alternating current (AC) light emitting diodes (LEDs) have been fabricated where Langmuir-Blodgett (LB) films of quinquethiophene (QT) or poly(3-hexylthiophene) (PHT) have been used as the active material sandwiched between insulating LB layers of poly(methylmethacrylate) (PMMA) or emeraldine base polyaniline (PANI), respectively. The frequency response of the devices has been studied, and as the frequency limit of operation we have used the -3 dB frequency. We have shown that high frequency AC LEDs can be fabricated with as few as 10-15 LB layers of the active material. Electroluminescence (EL) is observed almost equal in intensity in both biases for PMMA/QT/PMMA devices. The EL spectrum for these devices shows a broadening to the low-energy side as compared with the photoluminescence (PL) spectrum. The role of the interfaces for the frequency response is discussed

ELECTRON SPIN RESONANCE STUDIES OF MAGNETIC DEFECTS IN FeCl3-DOPED POLYPARAPHENYLENE (p-C6H4) x

Nous avons étudié les spectres RPE du (C6H4)x dopé avec FeCl3. La concentration en spins de type Curie, la dépendance avec T de la largeur de raie et un shift du facteur g dus au dopage sont interprétés en terme de formation de polarons et bipolarons. Dans le matériau fortement dopé, l'espèce Fe3+ de haut spin donnant des largeurs de raie importantes a été identifiée.ESR spectra of FeCl3 -doped (C6H4)x have been studied. The concentration of Curie-law spins, T-dependence of the linewidth and a shift in the g-factor due to doping are accounted for by polaron and bipolaron formation in doped samples. In heavily doped material high Fe3+ spin densities with broad linewidths were found

Light-emitting diodes using quinquethiophene Langmuir-Blodgett films: effect of electron-transporting layers

Langmuir-Blodgett (LB) films of quinquethiophene have been used as active emitting layers to fabricate light-emitting diodes. Green electroluminescence was visible in a dark room. The effect of the thickness of the film on the electroluminescence efficiency has been investigated. Even 5 LB layers have been shown to yield the same luminance as thicker films. Additional LB films of electron-transporting material have been used to increase the quantum efficiency, which has also resulted in a lower "turn-on" current for the device. The electroluminescence spectrum showed a profile identical to the photoluminescence spectrum of quinquethiophene

Electrical transport and optical properties of tetraanilinobenzene Langmuir-Blodgett films

We report a study of the electrical and optical properties of Langmuir-Blodgett films of tetraanilinobenzene. The optical absorption, peaking at 4.1 eV, is blue shifted by 0.2 eV, and photoluminescence, peaking at 3.0 eV, is red shifted by 0.4 eV compared to the material in solutions, indicating H aggregates. p-type doping by iodine gas or protonation in acidic solutions results in two polaronic subgap absorption bands and leads to an increase in conductivity from 10-10 to about 10-4 S/cm. The optical properties and doping mechanisms have been discussed and compared to those of vacuum-evaporated films. The oxidized units as well as polaronic states were found to act as nonradiative recombination centers for excitons. The conductivity s of the protonation-doped samples has a temperature T dependence logσ ∝T-1/2 indicating variable-range hopping in a quasigap, probably due to the Coulomb interactions between localized carriers in polaronic states. The nonohmic region was studied for moderately high electric fields up to 105 V/cm