Functional role of beta 1 integrin-mediated signalling in the human hair follicle

Integrins are transmembrane adhesion proteins that convey critical topobiological information and exert crucial signalling functions. In skin and hair follicle biology, beta1 integrins and their ligands are of particular interest. It is not yet known whether beta1 integrins play any role in the regulation of human hair growth and the expression pattern of beta1 integrin in the human pilosebaceous unit remains ill-defined. Here, we show that pilosebaceous immunoreactivity for beta1 integrin is most prominent in the outermost layer of the outer root sheath and the surrounding connective tissue sheath of human scalp hair follicles in situ and in vitro. Sites of beta1 integrin immunoreactivity co-express fibronectin and tenascin-C. Contrary to previous reports, beta1 integrin immunoreactivity in situ was not significantly upregulated in the human bulge region. Functionally, two beta1 integrin-activating antibodies (12G10, TS2/16) and ligand-mimicking RGD peptides promoted the growth of microdissected, organ-cultured human scalp hair follicles in vitro and inhibited spontaneous hair follicle regression. This supports the concept that beta1 integrin-mediated signalling is also important in human hair growth control. The physiologically relevant organ culture assay employed here is a potential research tool for exploring whether targeted stimulation of beta1 integrin-mediated signalling is a suitable candidate for human hair loss management.     

Dominance–diversity relationships in ant communities differ with invasion

The relationship between levels of dominance and species richness is highly contentious, especially in ant communities. The dominance‐impoverishment rule states that high levels of dominance only occur in species‐poor communities, but there appear to be many cases of high levels of dominance in highly diverse communities. The extent to which dominant species limit local richness through competitive exclusion remains unclear, but such exclusion appears more apparent for non‐native rather than native dominant species. Here we perform the first global analysis of the relationship between behavioral dominance and species richness. We used data from 1,293 local assemblages of ground‐dwelling ants distributed across five continents to document the generality of the dominance‐impoverishment rule, and to identify the biotic and abiotic conditions under which it does and does not apply. We found that the behavioral dominance–diversity relationship varies greatly, and depends on whether dominant species are native or non‐native, whether dominance is considered as occurrence or relative abundance, and on variation in mean annual temperature. There were declines in diversity with increasing dominance in invaded communities, but diversity increased with increasing dominance in native communities. These patterns occur along the global temperature gradient. However, positive and negative relationships are strongest in the hottest sites. We also found that climate regulates the degree of behavioral dominance, but differently from how it shapes species richness. Our findings imply that, despite strong competitive interactions among ants, competitive exclusion is not a major driver of local richness in native ant communities. Although the dominance‐impoverishment rule applies to invaded communities, we propose an alternative dominance‐diversification rule for native communities.     

Complement C3 Drives Autophagy-Dependent Restriction of Cyto-invasive Bacteria

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LOCALIZATION OF Na+, K+-ATPASE AND OTHER ENZYMES IN TELEOST PSEUDOBRANCH : II. Morphological Characterization of Intact Pseudobranch, Subcellular Fractions, and Plasma Membrane Substructure

The pseudobranch of the pinfish Lagodon rhomboides is an unusually homogeneous and structurally simple tissue, well suited to cell fractionation studies. Its principal cell type, closely related to the chloride cells of teleost gill, is characterized by numerous mitochondria in close association with abundant tubular invaginations of the plasma membrane. Other cytoplasmic organelles are rarely encountered. In broken fresh pseudobranch cells negatively stained with ammonium molybdate, a 40 Å particulate layer was observed on the intracellular surface of the tubular plasma membrane fragments. Nuclear (N), mitochondrial-light mitochondrial (M+L), and microsomal (P) fractions, obtained by differential centrifugation, were characterized by examination of fixed, embedded pellets and unfixed preparations negatively stained with ammonium molybdate and potassium phosphotung-state. Mitochondria, in orthodox configuration and retaining their outer membranes, were observed in M+L and N. Significant amounts of tubular, sheetlike, or vesicular membrane fragments were observed in all three fractions. Many such fragments, when negatively stained, showed the 40 Å particulate surface layer characteristic of plasma membrane invaginations, and in some cases 20-Å projections could be resolved on the opposite (extracellular) surface. Since these morphological observations, together with previously presented biochemical data, suggest a plasma membrane localization of Na⁺, K⁺-ATPase, the possible association of the enzyme with membrane projections is discussed.