Pericellular fibronectin is required for RhoA-dependent responses to cyclic strain in fibroblasts

To test the hypothesis that the pericellular fibronectin matrix is involved in mechanotransduction, we compared the response of normal and fibronectin-deficient mouse fibroblasts to cyclic substrate strain. Normal fibroblasts seeded on vitronectin in fibronectin-depleted medium deposited their own fibronectin matrix. In cultures exposed to cyclic strain, RhoA was activated, actin-stress fibers became more prominent, MAL/MKL1 shuttled to the nucleus, and mRNA encoding tenascin-C was induced. By contrast, these RhoA-dependent responses to cyclic strain were suppressed in fibronectin knockdown or knockout fibroblasts grown under identical conditions. On vitronectin substrate, fibronectin-deficient cells lacked fibrillar adhesions containing alpha5 integrin. However, when fibronectin-deficient fibroblasts were plated on exogenous fibronectin, their defects in adhesions and mechanotransduction were restored. Studies with fragments indicated that both the RGD-synergy site and the adjacent heparin-binding region of fibronectin were required for full activity in mechanotransduction, but not its ability to self-assemble. In contrast to RhoA-mediated responses, activation of Erk1/2 and PKB/Akt by cyclic strain was not affected in fibronectin-deficient cells. Our results indicate that pericellular fibronectin secreted by normal fibroblasts is a necessary component of the strain-sensing machinery. Supporting this hypothesis, induction of cellular tenascin-C by cyclic strain was suppressed by addition of exogenous tenascin-C, which interferes with fibronectin-mediated cell spreading.

Pulsatile shear and Gja5 modulate arterial identity and remodeling events during flow-driven arteriogenesis

In the developing chicken embryo yolk sac vasculature, the expression of arterial identity genes requires arterial hemodynamic conditions. We hypothesize that arterial flow must provide a unique signal that is relevant for supporting arterial identity gene expression and is absent in veins. We analyzed factors related to flow, pressure and oxygenation in the chicken embryo vitelline vasculature in vivo. The best discrimination between arteries and veins was obtained by calculating the maximal pulsatile increase in shear rate relative to the time-averaged shear rate in the same vessel: the relative pulse slope index (RPSI). RPSI was significantly higher in arteries than veins. Arterial endothelial cells exposed to pulsatile shear in vitro augmented arterial marker expression as compared with exposure to constant shear. The expression of Gja5 correlated with arterial flow patterns: the redistribution of arterial flow provoked by vitelline artery ligation resulted in flow-driven collateral arterial network formation and was associated with increased expression of Gja5. In situ hybridization in normal and ligation embryos confirmed that Gja5 expression is confined to arteries and regulated by flow. In mice, Gja5 (connexin 40) was also expressed in arteries. In the adult, increased flow drives arteriogenesis and the formation of collateral arterial networks in peripheral occlusive diseases. Genetic ablation of Gja5 function in mice resulted in reduced arteriogenesis in two occlusion models. We conclude that pulsatile shear patterns may be central for supporting arterial identity, and that arterial Gja5 expression plays a functional role in flow-driven arteriogenesis.

A Bentonite Deposit near Warm Springs, Montana

This report deals with a bentonite deposit recently developed, approximately seven miles northeast of Warm Springs, Montana. A group of claims have been staked on the deposit and are owned by the Lincoln Mining Company of Anaconda, Montana. The company also has several claims prospected for silver one mile from its present site of operations, but the silver prospects have failed to produce. The bentonite deposit was discovered incidentally during the course of other development work, and at present two adits have been driven into the side of a mountain, each crosscutting a vein-like mass of bentonite varying from two to three feet in width.

Zinc Plating Magnesium

Magnesium and magnesium alloys are becoming more and more important in modern industry. Their use in the aviation industry has been greatly curtailed because of their comparatively poor resistance to corrosion especially in moist atmospheres. Many methods have been adopted to improve their resistance to corrosion.

Tenascin-C and tenascin-W in whisker follicle stem cell niches: possible roles in regulating stem cell proliferation and migration

The whisker follicle has CD34-positive stem cells that migrate from their niche near the bulge along the glassy membrane to the whisker bulb, where they participate in the formation of the whisker shaft. Using immunohistochemistry we found the glycoprotein tenascin-C in the fibrous capsule of mouse whisker follicles, along the glassy membrane and in the trabecular region surrounding keratin-15-negative, CD34-positive stem cells. The related glycoprotein tenascin-W is found in the CD34-positive stem cell niche, in nearby trabeculae, and along the glassy membrane. Tenascin-W is also found in the neural stem cell niche of nearby hair follicles. The formation of stress fibers and focal adhesion complexes in CD34-positive whisker-derived stem cells cultured on fibronectin was inhibited by both tenascin-C and tenascin-W, which is consistent with a role for these glycoproteins in promoting the migration of these cells from the niche to the whisker bulb. Tenascin-C, but not tenascin-W, increased the proliferation of whisker follicle stem cells in vitro. Thus, the CD34-positive whisker follicle stem cell niche contains both tenascin-C and tenascin-W, and these glycoproteins may play a role in directing the migration and proliferation of these stem cells.