Despite their importance in cell biology, the mechanisms that maintain the nucleus in its proper position in the cell are not well understood. This is primarily the result of an incomplete knowledge of the proteins in the outer nuclear membrane (ONM) that are able to associate with the different cytoskeletal systems. Two related ONM proteins, nuclear envelope spectrin repeat (nesprin)–1 and –2, are known to make direct connections with the actin cytoskeleton through their NH2-terminal actin-binding domain (ABD). We have now isolated a third member of the nesprin family that lacks an ABD and instead binds to the plakin family member plectin, which can associate with the intermediate filament (IF) system. Overexpression of nesprin-3 results in a dramatic recruitment of plectin to the nuclear perimeter, which is where these two molecules are colocalized with both keratin-6 and -14. Importantly, plectin binds to the integrin α6β4 at the cell surface and to nesprin-3 at the ONM in keratinocytes, suggesting that there is a continuous connection between the nucleus and the extracellular matrix through the IF cytoskeleton.

Hereditary hemorrhagic telangiectasia (HHT) is an inherited disorder characterized by vascular malformations. Many affected individuals develop recurrent nosebleeds, which can severely affect their quality of life and are clinically difficult to treat. We report here that treatment with thalidomide reduced the severity and frequency of nosebleeds (epistaxis) in the majority of a small group of subjects with HHT tested. The blood hemoglobin levels of the treated individuals rose as a result of reduced hemorrhage and enhanced blood vessel stabilization. In mice heterozygous for a null mutation in the Eng gene (encoding endoglin), an experimental model of HHT, thalidomide treatment stimulated mural cell coverage and thus rescued vessel wall defects. Thalidomide treatment increased platelet-derived growth factor-B (PDGF-B) expression in endothelial cells and stimulated mural cell activation. The effects of thalidomide treatment were partially reversed by pharmacological or genetic interference with PDGF signaling from endothelial cells to pericytes. Biopsies of nasal epithelium from individuals with HHT treated or not with thalidomide showed that similar mechanisms may explain the effects of thalidomide treatment in humans. Our findings demonstrate the ability of thalidomide to induce vessel maturation, which may be useful as a therapeutic strategy for the treatment of vascular malformations.

flox/flox; K14-Cre mice lacking the α3 subunit specifically in the basal layer of the epidermis. These mice are viable but display several skin defects, including local inflammation, hair loss, basement membrane duplication and microblistering at the dermalepidermal junction, whereas hemidesmosome assembly and keratinocyte differentiation are not impaired. Wound healing is slightly faster in the absence of integrin α3β1, whereas proliferation, the distribution of other integrins and the deposition of basement membrane proteins in the wound bed are unaltered. In vitro, cell spreading is rescued by increased surface expression of α6β1 integrin in the absence of integrin α3. The α3-deficient keratinocytes migrate with an increased velocity and persistence, whereas proliferation, growth factor signaling, hemidesmosome assembly, and laminin-332 deposition appeared to be normal. We suggest that integrin α3β1 delays keratinocyte migration during wound reepithelialization, by binding to the laminin-332 that is newly deposited on the wound bed.Supplementary material available online at

We addressed the potential role of cell-laminin interactions during epaxial myotome formation in the mouse embryo. Assembly of the myotomal laminin matrix occurs as epaxial myogenic precursor cells enter the myotome. Most Myf5-positive and myogeninnegative myogenic precursor cells localise near assembled laminin, while myogenin-expressing cells are located either away from this matrix or in areas where it is being assembled. In Myf5 nlacZ/nlacZ (Myf5-null) embryos, laminin, collagen type IV and perlecan are present extracellularly near myogenic precursor cells, but do not form a basement membrane and cells are not contained in the myotomal compartment. Unlike wild-type myogenic precursor cells, Myf5-null cells do not express the ␣6␤1 integrin, a laminin receptor, suggesting that integrin ␣6␤1-laminin interactions are required for myotomal laminin matrix assembly. Blocking ␣6␤1-laminin binding in cultured wild-type mouse embryo explants resulted in dispersion of Myf5-positive cells, a phenotype also seen in Myf5 nlacZ/nlacZ embryos. Furthermore, inhibition of ␣6␤1 resulted in an increase in Myf5 protein and ectopic myogenin expression in dermomyotomal cells, suggesting that ␣6␤1-laminin interactions normally repress myogenesis in the dermomyotome. We conclude that Myf5 is required for maintaining ␣6␤1 expression on myogenic precursor cells, and that ␣6␤1 is necessary for myotomal laminin matrix assembly and cell guidance into the myotome. Engagement of laminin by ␣6␤1 also plays a role in maintaining the undifferentiated state of cells in the dermomyotome prior to their entry into the myotome.

distribution of a range of adhesion receptors and basement membrane proteins was unaltered. Moreover, loss of α6β4 did not affect squamous differentiation, proliferation or survival, except for areas in which keratinocytes had detached from the basement membrane. These in vivo observations were confirmed in vitro by using immortalized keratinocytes -derived from β4-subunit conditional knockout mice -from which the gene encoding β4 had been deleted by Cre-mediated recombination. Consistent with the established role of α6β4 in adhesion strengthening, its loss from cells was found to increase their motility. Our findings clearly demonstrate that, after birth, epidermal differentiation, proliferation and survival all proceed normally in the absence of α6β4, provided that cell adhesion is not compromised.