Posts Tagged ‘Substrates’

Holding tight on feathers – structural specializations and attachment properties of the avian ectoparasite Crataerina pallida (Diptera, Hippoboscidae) [RESEARCH ARTICLE]

Dennis S. Petersen, Nils Kreuter, Lars Heepe, Sebastian Büsse, Arndt H. J. Wellbrock, Klaudia Witte, and Stanislav N. GorbThe louse fly Crataerina pallida is an obligate blood-sucking ecto-parasite of the common swift Apus apus. Due to reducti…

Force loading explains spatial sensing of ligands by cells

Cells can sense the density and distribution of extracellular matrix (ECM) molecules by means of individual integrin proteins and larger, integrin-containing adhesion complexes within the cell membrane. This spatial sensing drives cellular activity in a variety of normal and pathological contexts. Previous studies of cells on rigid glass surfaces have shown that spatial sensing of ECM ligands takes place at the nanometre scale, with integrin clustering and subsequent formation of focal adhesions impaired when single integrin–ligand bonds are separated by more than a few tens of nanometres. It has thus been suggested that a crosslinking ‘adaptor’ protein of this size might connect integrins to the actin cytoskeleton, acting as a molecular ruler that senses ligand spacing directly. Here, we develop gels whose rigidity and nanometre-scale distribution of ECM ligands can be controlled and altered. We find that increasing the spacing between ligands promotes the growth of focal adhesions on low-rigidity substrates, but leads to adhesion collapse on more-rigid substrates. Furthermore, disordering the ligand distribution drastically increases adhesion growth, but reduces the rigidity threshold for adhesion collapse. The growth and collapse of focal adhesions are mirrored by, respectively, the nuclear or cytosolic localization of the transcriptional regulator protein YAP. We explain these findings not through direct sensing of ligand spacing, but by using an expanded computational molecular-clutch model, in which individual integrin–ECM bonds—the molecular clutches—respond to force loading by recruiting extra integrins, up to a maximum value. This generates more clutches, redistributing the overall force among them, and reducing the force loading per clutch. At high rigidity and high ligand spacing, maximum recruitment is reached, preventing further force redistribution and leading to adhesion collapse. Measurements of cellular traction forces and actin flow speeds support our model. Our results provide a general framework for how cells sense spatial and physical information at the nanoscale, precisely tuning the range of conditions at which they form adhesions and activate transcriptional regulation.


Methods and kits which utilize a conjugate, preferably an adduct, of ergosterol for determining the presence or level of a broad spectrum of ergosterol-containing organisms (e.g., fungi) in various substrates are disclosed. These methods and kits can b…

Two distinct RNase activities of CRISPR-C2c2 enable guide-RNA processing and RNA detection

Bacterial adaptive immune systems use CRISPRs (clustered regularly interspaced short palindromic repeats) and CRISPR-associated (Cas) proteins for RNA-guided nucleic acid cleavage. Although most prokaryotic adaptive immune systems generally target DNA substrates, type III and VI CRISPR systems direct interference complexes against single-stranded RNA substrates. In type VI systems, the single-subunit C2c2 protein functions as an RNA-guided RNA endonuclease (RNase). How this enzyme acquires mature CRISPR RNAs (crRNAs) that are essential for immune surveillance and how it carries out crRNA-mediated RNA cleavage remain unclear. Here we show that bacterial C2c2 possesses a unique RNase activity responsible for CRISPR RNA maturation that is distinct from its RNA-activated single-stranded RNA degradation activity. These dual RNase functions are chemically and mechanistically different from each other and from the crRNA-processing behaviour of the evolutionarily unrelated CRISPR enzyme Cpf1 (ref. 11). The two RNase activities of C2c2 enable multiplexed processing and loading of guide RNAs that in turn allow sensitive detection of cellular transcripts.

Effects of support diameter and compliance on common marmoset (Callithrix jacchus) gait kinematics [RESEARCH ARTICLE]

Jesse W. Young, Bethany M. Stricklen, and Brad A. Chadwell
Locomotion is precarious in an arboreal habitat, where supports can vary in both diameter and level of compliance. Several previous studies have evaluated the influence of substrate diameter o…

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