Loss of N-cadherin from the endothelium causes stromal edema and epithelial dysgenesis in the mouse cornea.

PURPOSE: We analyzed the role of N-cadherin in maintaining proper architecture and function of corneal endothelium. METHODS: To achieve specific removal of N-cadherin from corneal endothelium, we bred mice carrying a floxed N-cadherin gene with those expressing the Cre-recombinase gene under the control of P0 promoter. The corneal structure was analyzed by immunostaining for cell junction proteins as well as by electron microscopy. The apoptotic status was assessed by TUNEL staining. The permeability of corneal endothelium was evaluated using fluorescein dye. RESULTS: Removal of endothelial N-cadherin led to the appearance of opacity in the adult corneas. All corneal layers exhibited histological defects: The apical junctional complex (AJC) in corneal endothelium was disorganized, losing the continuity in tight junctions. Collagen fibrils were rearranged in the stroma. The corneal epithelium showed decreased thickness and TUNEL staining revealed increased central areas of apoptosis. Fluorescein dye injection in the anterior chamber confirmed an increased permeability of the endothelial layer. Developmental analysis indicated that, although N-cadherin was lost during embryonic stages, the AJC was maintained normally until early postnatal stages, probably due to the presence of other cadherins at these developmental stages. The junctional defects in endothelial cells, however, became obvious by postnatal day 21 (P21), although stromal and epithelial phenotypes were clearly detectable only in the adult eyes. CONCLUSIONS: N-cadherin is essential for maintaining proper structure of corneal endothelial AJCs from late postnatal to adult stages. Its ablation leads to increased endothelial permeability and corneal edema in mature eyes.

Pax2 modulates proliferation during specification of the otic and epibranchial placodes.

BACKGROUND: The inner ear and epibranchial ganglia of vertebrates arise from a shared progenitor domain that is induced by FGF signalling, the posterior placodal area (PPA), before being segregated by Wnt signalling. One of the first genes activated in the PPA is the transcription factor Pax2. Loss-of- and gain-of function studies have defined a role for Pax2 in placodal morphogenesis and later inner ear development, but have not addressed the role Pax2 plays during the formation and maintenance of the PPA. RESULTS: To understand the role of Pax2 during the development of the PPA, we used over-expression and repression of Pax2. Both gave rise to a smaller otocyst and repressed the formation of epibranchial placodes. In addition, cell cycle analysis revealed that Pax2 suppression reduced proliferation of the PPA. CONCLUSIONS: Our results suggest that Pax2 functions in the maintenance but not the induction of the PPA. One role of Pax2 is to maintain proper cell cycle proliferation in the PPA.

Constitutive diffuse activation of phosphoinositide 3-kinase at the plasma membrane by v-Src suppresses the chemotactic response to PDGF by abrogating the polarity of PDGF receptor signalling.

Cancer cells depend on chemotaxis for invasion and frequently overexpress and/or activate Src. We previously reported that v-Src accelerates motility by promoting phosphoinositide 3-kinase (PI3-K) signalling but abrogates chemotaxis. We here addressed the mechanism of the loss of chemotactic response to platelet-derived growth factor (PDGF) gradients in fibroblasts harbouring a thermosensitive v-Src kinase. At non-permissive temperature, PDGF receptor (PDGFR) signalling, assessed by phosphoY(751)-specific antibodies (a docking site for PI3-K), was not detected without PDGF and showed a concentration-dependent PDGF response. Both immunolabeling of PI3-K (p110) and live cell imaging of its product (phosphatidylinositol 3,4,5 tris-phosphate) showed PI3-K recruitment and activation at lamellipodia polarized towards a PDGF gradient. Centrosomes and PDGFR- and Src-bearing endosomes were also oriented towards this gradient. Upon v-Src thermoactivation, (i) Y(751) phosphorylation was moderately induced without PDGF and synergistically increased with PDGF; (ii) PI3-K was recruited and activated all along the plasma membrane without PDGF and did not polarize in response to a PDGF gradient; and (iii) polarization of centrosomes and of PDGFR-bearing endosomes were also abrogated. Thus, PDGF can further increase PDGFR auto-phosphorylation despite strong Src kinase activity, but diffuse downstream activation of PI3-K by Src abrogates cell polarization and chemotaxis: "signalling requires silence".