Actin Dynamics in Muscle Cells

In every cell, actin is a key component involved in migration, cytokinesis, endocytosis and generation of contraction. In non-muscle cells, actin filaments are very dynamic and regulated by an array of proteins that interact with actin filaments and/or monomeric actin. Interestingly, in non-muscle cells the barbed ends of the filaments are the predominant assembly place, whereas in muscle cells actin dynamics was reported to predominate at the pointed ends of thin filaments. The actin-based thin filament pointed (slow growing) ends extend towards the middle of the sarcomere's M-line where they interact with the thick filaments to generate contraction. The actin filaments in muscle cells are organized into a nearly crystalline array and are believed to be significantly less dynamic than the ones in other cell types. However, the exact mechanisms of the sarcomere assembly and turnover are largely unknown. Interestingly, although sarcomeric actin structures are believed to be relatively non-dynamic, many proteins promoting actin dynamics are expressed also in muscle cells (e.g ADF/cofilin, cyclase-associated protein and twinfilin). Thus, it is possible that the muscle-specific isoforms of these proteins promote actin dynamics differently from their non-muscle counterparts, or that actin filaments in muscle cells are more dynamic than previously thought. To study protein dynamics in live muscle cells, I used primary cell cultures of rat cardiomyocytes. My studies revealed that a subset of actin filaments in cardiomyocyte sarcomeres displays rapid turnover. Importantly, I discovered that the turnover of actin filaments depends on contractility of the cardiomyocytes and that the contractility-induced actin dynamics plays an important role in sarcomere maturation. Together with previous studies those findings suggest that sarcomeres undergo two types of actin dynamics: (1) contractility-dependent turnover of whole filaments and (2) regulatory pointed end monomer exchange to maintain correct thin filament length. Studies involving an actin polymerization inhibitor suggest that the dynamic actin filament pool identified here is composed of filaments that do not contribute to contractility. Additionally, I provided evidence that ADF/cofilins, together with myosin-induced contractility, are required to disassemble non-productive filaments in developing cardiomyocytes. In addition, during these studies we learned that isoforms of actin monomer binding protein twinfilin, Twf-1 and Twf-2a localise to myofibrils in cardiomyocytes and may thus contribute to actin dynamics in myofibrils. Finally, in collaboration with Roberto Dominguez s laboratory we characterized a new actin nucleator in muscle cells - leiomodin (Lmod). Lmod localises towards actin filament pointed ends and its depletion by siRNA leads to severe sarcomere abnormalities in cardiomyocytes. The actin filament nucleation activity of Lmod is enhanced by interactions with tropomyosin. We also revealed that Lmod expression correlates with the maturation of myofibrils, and that it associates with sarcomeres only at relatively late stages of myofibrillogenesis. Thus, Lmod is unlikely to play an important role in myofibril formation, but rather might be involved in the second step of the filament arrangement and/or maintenance through its ability to promote tropomyosin-induced actin filament nucleation occurring at the filament pointed ends. The results of these studies provide valuable new information about the molecular mechanisms underlying muscle sarcomere assembly and turnover. These data offer important clues to understanding certain physiological and pathological behaviours of muscle cells. Better understanding of the processes occurring in muscles might help to find strategies for determining, diagnosis, prognosis and therapy in heart and skeletal muscles diseases.Human heart cells - cardiomoycytes - are constantly contracting cells; about three billion times during an average lifespan - to pump in average 7000 litres of blood per day. To ensure its proper function the multiprotein cytoskeletal complexes (myofibrils) have to be assembled and maintained correctly. The myofibrils consist of set of filaments organized in a paracrystal structure - sarcomere - to ensure maximal contractile force. Sarcomeres are composed by actin and myosin filaments. Their proper interaction is regulated and accompany by vary type of supporting proteins. The actin filaments in muscle cells are organized into a nearly crystalline array and are believed to be significantly less dynamic than the ones in other cell types (eg. skin cells). However, the exact mechanisms of the sarcomere assembly and turnover are largely unknown. This study revealed that two types of actin dynamics exist in muscle cells. First, actin filaments undergo slow dynamics at their ends to maintain the correct length of the filaments. Secondly, entire actin filaments are replaced by new ones during sarcomere assembly and maintenance, and this phenomenon is dependent on the contractility of the muscle cells. Finally, we characterized a new actin-binding protein, Lmod, which nucleates the formation of new actin filaments in muscle cells. These data provide valuable new information about the molecular mechanisms underlying muscle sarcomere assembly and turnover. These data offer important clues to understanding certain physiological and pathological behaviours of muscle cells. Better understanding of the processes occurring in muscles might help to find strategies for determining, diagnosis, prognosis and therapy in heart and skeletal muscles diseases

Processing facial expressions of emotion: upright vs. inverted images

We studied discrimination of briefly presented upright vs. inverted emotional facial expressions (FEs), hypothesizing that inversion would impair emotion decoding by disrupting holistic FE processing. Stimuli were photographs of seven emotion prototypes, of a male and female poser (Ekman and Friesen, 1976), and eight intermediate morphs in each set. Subjects made speeded Same/Different judgments of emotional content for all upright (U) or inverted (I) pairs of FEs, presented for 500 ms, 100 times each pair. Signal Detection Theory revealed the sensitivity measure d′ to be slightly but significantly higher for the upright FEs. In further analysis using multidimensional scaling (MDS), percentages of Same judgments were taken as an index of pairwise perceptual similarity, separately for U and I presentation mode. The outcome was a 4D “emotion expression space,” with FEs represented as points and the dimensions identified as Happy–Sad, Surprise/Fear, Disgust, and Anger. The solutions for U and I FEs were compared by means of cophenetic and canonical correlation, Procrustes analysis, and weighted-Euclidean analysis of individual differences. Differences in discrimination produced by inverting FE stimuli were found to be small and manifested as minor changes in the MDS structure or weights of the dimensions. Solutions differed substantially more between the two posers, however. Notably, for stimuli containing elements of Happiness (whether U or I), the MDS structure showed signs of implicit categorization, indicating that mouth curvature – the dominant feature conveying Happiness – is visually salient and receives early processing. The findings suggest that for briefly presented FEs, Same/Different decisions are dominated by low-level visual analysis of abstract patterns of lightness and edge filters, but also reflect emerging featural analysis. These analyses, insensitive to face orientation, enable initial positive/negative Valence categorization of FEs

Influence of the Modifier Type and its Concentration on Electroosmotic Flow of the Mobile Phase in Pressurized Planar Electrochromatography

The aim of this work was to find a relationship between electroosmotic flow (EOF) velocity of the mobile phase in pressurized planar electrochromatography (PPEC) and physicochemical properties like zeta potential, dielectric constant, and viscosity of the mobile phase as well as its composition. The study included different types of organic modifiers (acetonitrile, methanol, ethanol, acetone, formamide, N-methylformamide and N,N-dimethylformamide) in the full concentration range. In all experiments, chromatographic glass plates HPTLC RP-18 W from Merck (Darmstadt) were used as a stationary phase. During the study we found that there is no linear correlation between EOF velocity of the mobile phase and single variables such as zeta potential or dielectric constant or viscosity. However, there is quite strong linear correlation between EOF velocity of the mobile phase and variable obtained by multiplying zeta potential of the stationary phase–mobile phase interface, by dielectric constant of the mobile phase solution and dividing by viscosity of the mobile phase. Therefore, it could be concluded that the PPEC system fulfilled the Helmholtz–Smoluchowski equation

The Influence of Carbonate Ions on the Structure of the Electrical Double Layer at the Interface of Hydroxyapatite/Electrolyte Solution

The aim of the work was to investigate the changes in the double electrical layer at the hydroxyapatite containing different amount of carbonate ions/electrolyte solution. Besides, the main properties of the edl (electrical double layer), i.e. surface charge density and zeta potential were determined by electrophoresis measurements and potentiometer titration, respectively. The synthesized adsorbents were characterized by the following methods: X-ray diffraction, FTIR (Fourier Transform Infrared Spectroscopy), adsorption and desorption of nitrogen and scanning electron microscopy. The analyzed samples had different structures and particle sizes. It was proved that increase in the carbonate groups content is connected with the decrease of apatite grain sizes and crystallinity reduction. The characteristic parameters of the electric double layer were also different: pHpzc (point zero of charge) of hydroxyapatite was 6.5 whereas for carbonate apatite was higher – pHpzc = 8. In both cases determination of precise pHIEP (isoelectric point) was not possible but it is known that its value is lower than 4

An analysis and simulation of an emergency department with aims towards improving network flow and efficiency of care

The purpose of this project is to help improve E.R. operations, by minimizing patient wait times and utilizing resources fully and properly. One of the biggest issues in an ER is effectively serving all patients quickly without over burdening the human resources of the system. To do so staff must be utilized correctly, patients prioritized, and processes optimized and balanced within the system. However, many hospitals have very little data on actual times within the system or a true understanding of where delays occur. The project will seek to both determine what processes in the hospital are most detrimental to patient wait times along with giving the hospital recommendations on how to improve wait times and resource utilization. Ultimately the goal is for a system that will allow them to better serve their patients

Postulat upraszczania pism urzędowych i decyzji administracyjnych w prawie krajowym

The article outlines the sources of difficulties in fulfilling the demands of the plain language movement in Polish law. It also indicates why the demand for plain language is insufficient and under what conditions it can be realised. Simply put, it would be harmful to attempt the implementation of the model of simplification of official documents and administrative decisions without appropriate assessment of the impact of such simplicity on the application and creation of law, as understood by doctrine. In order to avoid this, it is necessary to clarify the theoretical and legal conditions that are likely to translate into legislative practice. The article discusses the possibility of reaching an agreement regarding the validity and content of these conditions.W artykule nakreślono przyczyny trudności w spełnieniu postulatów ruchu plainlanguage w prawie polskim oraz wskazano, dlaczego roszczenie o prosty język jest niewystarczające i przy założeniu jakich warunków aktualizuje się. Przeniesienie na system prawa modelu upraszczania pism urzędowych i decyzji administracyjnych, bez oceny tak ujętej prostoty w warunkach stosowania prawa i procesie jego tworzenia, byłoby działaniem po prostu szkodliwym. Aby tak się nie stało, konieczne jest doprecyzowanie warunków teoretycznoprawnych mających szansę przełożyć się na praktykę prawodawczą. Artykuł traktuje o możliwości porozumienia się co do ich słuszności i treści