A key role is emerging for the cytoskeleton in coordinating receptor signaling, although the underlying molecular requirements remain unclear. Here we show that cytoskeleton disruption triggered ...signaling requiring not only the B cell receptor (BCR), but also the coreceptor CD19 and tetraspanin CD81, thus providing a mechanism for signal amplification upon surface-bound antigen stimulation. By using superresolution microscopy, we demonstrated that endogenous IgM, IgD, and CD19 exhibited distinct nanoscale organization within the plasma membrane of primary B cells. Upon stimulation, we detect a local convergence of receptors, although their global organization was not dramatically altered. Thus, we postulate that cytoskeleton reorganization releases BCR nanoclusters, which can interact with CD19 held in place by the tetraspanin network. These results not only suggest that receptor compartmentalization regulates antigen-induced activation but also imply a potential role for CD19 in mediating ligand-independent “tonic” BCR signaling necessary for B cell survival.
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► In resting cells, the BCR and the coreceptor CD19 are organized in nanoclusters ► Differential compartmentalization of the BCR and CD19 is important for BCR signaling ► Disruption of the actin cytoskeleton triggers signaling through the BCR and CD19 ► This antigen-independent signaling requires CD19 organized by the tetraspanin network
Abstract
In a project aimed at measuring the optical extragalactic background light (EBL), we are using the shadow of a dark cloud. We have performed, with the ESO VLT/FORS, spectrophotometry of the ...surface brightness towards the high-galactic-latitude dark cloud Lynds 1642. A spectrum representing the difference between the opaque core of the cloud and several unobscured positions around the cloud was presented in Paper I. The topic of this paper is the separation of the scattered starlight from the dark cloud itself which is the only remaining foreground component in this difference. While the scattered starlight spectrum has the characteristic Fraunhofer lines and the discontinuity at 400 nm, typical of integrated light of galaxies, the EBL spectrum is a smooth one without these features. As template for the scattered starlight, we make use of the spectra at two semitransparent positions. The resulting EBL intensity at 400 nm is I
EBL = 2.9 ± 1.1 10−9 erg cm−2 s−1 sr−1 Å−1 or 11.6 ± 4.4 nW m−2sr−1, which represents a 2.6σ detection; the scaling uncertainty is +20 per cent/−16 per cent. At 520 nm, we have set a 2σ upper limit of I
EBL ≤4.5 10−9 erg cm−2 s−1 sr−1 Å−1 or ≤ 23.4 nW m−2sr−1 +20 per cent/−16 per cent. Our EBL value at 400 nm is ≳ 2 times as high as the integrated light of galaxies. No known diffuse light sources, such as light from Milky Way halo, intra-cluster or intra-group stars appear capable of explaining the observed EBL excess over the integrated light of galaxies.
Recent evidence implicates the actin cytoskeleton in the control of receptor signaling. This may be of particular importance in the context of immune receptors, such as the B cell receptor, where ...dysregulated signaling can result in autoimmunity and malignancy. Here, we discuss the role of the actin cytoskeleton in controlling receptor compartmentalization, dynamics, and clustering as a means to regulate receptor signaling through controlling the interactions with protein partners. We propose that the actin cytoskeleton is a point of integration for receptor cross talk through modulation of protein dynamics and clustering. We discuss the implication of this cross talk via the cytoskeleton for both ligand-induced and low-level constitutive (tonic) signaling necessary for immune cell survival.
Even though the association between alexithymia and somatization seems plausible according to several studies with selected populations, it has not been verified in carefully controlled and ...nationally representative population studies. We conducted such a study to find out whether alexithymia is associated with somatization at population level.
This study was a part of the Finnish Health 2000 Study. The nationally representative sample comprised 5129 subjects aged 30 to 97 years. Alexithymia was measured with the 20-item Toronto Alexithymia Scale (TAS-20) and somatic symptom reporting with the 12-item somatization scale derived from the Hopkins Symptom Checklist. Sociodemographic and health-related variables, including depressive and anxiety disorders, and physician verified somatic diagnoses, were treated as confounders in multivariate analyses.
Alexithymia was associated with somatization independently of somatic diseases, depression and anxiety and confounding sociodemographic variables. The TAS-20 factor scale "Difficulties Identifying Feelings" was the strongest common denominator between alexithymia and somatization.
This was the first time the independent association between alexithymia and somatization was established in a large, nationally representative nonclinical sample of both young and old adults with and without mental disorders and somatic diseases.
Facilitated by the advancements in microscopy, our understanding of the complexity of intracellular vesicle traffic has dramatically increased in recent years. However, distinguishing between plasma ...membrane-bound or internalised ligands remains a major challenge for the studies of cargo sorting to endosomal compartments, especially in small and round cells such as lymphocytes. The specific hybridization internalisation probe (SHIP) assay, developed for flow cytometry studies, employs a ssDNA fluorescence internalisation probe and a complementary ssDNA quenching probe to unambiguously detect the internalized receptors/cargo. Here, we adopted the SHIP assay to study the trafficking of receptor/ligand complexes using B lymphocytes and B cell receptor-mediated antigen internalization as a model system. Our study demonstrates the potential of the SHIP assay for improving the imaging of internalized receptor/ligand complexes and establishes the compatibility of this assay with multiple imaging modalities, including live-cell imaging and super-resolution microscopy.
Abstract
We present the method and observations for the measurement of the Extragalactic Background Light (EBL) utilizing the shadowing effect of a dark cloud. We measure the surface brightness ...difference between the opaque cloud core and its unobscured surroundings. In the difference the large atmospheric and Zodiacal light components are eliminated and the only remaining foreground component is the scattered starlight from the cloud itself. Although much smaller, its separation is the key problem in the method. For its separation we use spectroscopy. While the scattered starlight has the characteristic Fraunhofer lines and 400 nm discontinuity, the EBL spectrum is smooth and without these features. Medium resolution spectrophotometry at λ = 380–580 nm was performed with VLT/FORS at ESO of the surface brightness in and around the high-galactic-latitude dark cloud Lynds 1642. Besides the spectrum for the core with AV
≳ 15 mag, further spectra were obtained for intermediate-opacity cloud positions. They are used as proxy for the spectrum of the impinging starlight spectrum and to facilitate the separation of the scattered starlight (cf. Paper II; Mattila et al.). Our spectra reach a precision of ≲ 0.5 × 10−9 erg cm−2 s−1 sr−1 Å−1 as required to measure an EBL intensity in range of ∼1 to a few times 10−9 erg cm−2 s−1 sr−1 Å−1. Because all surface brightness components are measured using the same equipment, the method does not require unusually high absolute calibration accuracy, a condition that has been a problem for some previous EBL projects.
ABSTRACT
We have performed a 5-colour surface photometric study of the high-galactic-latitude area of dark nebula LDN 1642. Scattered light properties are presented of diffuse, translucent, and ...opaque dust over the range of 3500–5500 Å . Far infrared absolute photometry at 200 µm improves the precision of and provides a zero point to the extinction. The intensity of the scattered light depends on dust column density in a characteristic way: for optically thin dust the intensity first increases linearly, then turns to a saturation value; at still larger extinctions the intensity turns down to a slow decrease. The AV value of the saturated intensity maximum shifts in a systematic way, from AV ≈ 1.5 mag at 3500 Å to ∼3 mag at 5500 Å . The intensity curves offer a straight-forward explanation for the behaviour of the scattered-light colours. At the intensity peak the colour agrees with the integrated starlight colour, while it is bluer at the low- and redder at the high-column-density side of the peak, respectively. These colour changes are a direct consequence of the wavelength dependence of the extinction. We have compared the colours of the LDN 1642 area with other relevant observational studies: high-latitude diffuse/translucent clouds, wide-field cirrus dust; and externally illuminated AGB-star envelopes. For extragalactic low-surface-brightness sources cirrus is an unwanted foreground contaminant. Our results for cirrus colours can help to distinguish cases where a diffuse plume or stream, apparently associated with a galaxy or a group or cluster, is more likely a local cirrus structure.
We investigated inbreeding depression and genetic load in a small (N ₑ ∼ 100) population of the Glanville fritillary butterfly (Melitaea cinxia), which has been completely isolated on a small island ...Pikku Tytärsaari (PT) in the Baltic Sea for at least 75 y. As a reference, we studied conspecific populations from the well-studied metapopulation in the Åland Islands (ÅL), 400 km away. A large population in Saaremaa, Estonia, was used as a reference for estimating genetic diversity and N ₑ. We investigated 58 traits related to behavior, development, morphology, reproductive performance, and metabolism. The PT population exhibited high genetic load (L = 1 − W PT/W ÅL) in a range of fitness-related traits including adult weight (L = 0.12), flight metabolic rate (L = 0.53), egg viability (L = 0.37), and lifetime production of eggs in an outdoor population cage (L = 0.70). These results imply extensive fixation of deleterious recessive mutations, supported by greatly reduced diversity in microsatellite markers and immediate recovery (heterosis) of egg viability and flight metabolic rate in crosses with other populations. There was no significant inbreeding depression in most traits due to one generation of full-sib mating. Resting metabolic rate was significantly elevated in PT males, which may be related to their short lifespan (L = 0.25). The demographic history and the effective size of the PT population place it in the part of the parameter space in which models predict mutation accumulation. This population exemplifies the increasingly common situation in fragmented landscapes, in which small and completely isolated populations are vulnerable to extinction due to high genetic load.
The actin cytoskeleton plays a fundamental role in various motile and morphogenetic processes involving membrane dynamics. We show that actin-binding proteins MIM (missing-in-metastasis) and IRSp53 ...directly bind PI(4,5)P₂-rich membranes and deform them into tubular structures. This activity resides in the N-terminal IRSp53/MIM domain (IMD) of these proteins, which is structurally related to membrane-tubulating BAR (Bin/amphiphysin/Rvs) domains. We found that because of a difference in the geometry of the PI(4,5)P₂-binding site, IMDs induce a membrane curvature opposite that of BAR domains and deform membranes by binding to the interior of the tubule. This explains why IMD proteins induce plasma membrane protrusions rather than invaginations. We also provide evidence that the membrane-deforming activity of IMDs, instead of the previously proposed F-actin-bundling or GTPase-binding activities, is critical for the induction of the filopodia/microspikes in cultured mammalian cells. Together, these data reveal that interplay between actin dynamics and a novel membrane-deformation activity promotes cell motility and morphogenesis.
Generation of membrane curvature is critical for the formation of plasma membrane protrusions and invaginations and for shaping intracellular organelles. Among the central regulators of membrane ...dynamics are the BAR superfamily domains, which deform membranes into tubular structures. In contrast to the relatively well characterized BAR and F-BAR domains that promote the formation of plasma membrane invaginations, I-BAR domains induce plasma membrane protrusions through a poorly understood mechanism.
We show that I-BAR domains induce strong PI(4,5)P
2 clustering upon membrane binding, bend the membrane through electrostatic interactions, and remain dynamically associated with the inner leaflet of membrane tubules. Thus, I-BAR domains induce the formation of dynamic membrane protrusions to the opposite direction than do BAR and F-BAR domains. Strikingly, comparison of different I-BAR domains revealed that they deform PI(4,5)P
2-rich membranes through distinct mechanisms. IRSp53 and IRTKS I-BARs bind membranes mainly through electrostatic interactions, whereas MIM and ABBA I-BARs additionally insert an amphipathic helix into the membrane bilayer, resulting in larger tubule diameter in vitro and more efficient filopodia formation in vivo. Furthermore, FRAP analysis revealed that whereas the mammalian I-BAR domains display dynamic association with filopodia, the
C. elegans I-BAR domain forms relatively stable structures inside the plasma membrane protrusions.
These data define I-BAR domain as a functional member of the BAR domain superfamily and unravel the mechanisms by which I-BAR domains deform membranes to induce filopodia in cells. Furthermore, our work reveals unexpected divergence in the mechanisms by which evolutionarily distinct groups of I-BAR domains interact with PI(4,5)P
2-rich membranes.
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