A Genetic Screen for Anchorage-Independent Proliferation in Mammalian Cells Identifies a Membrane-Bound Neuregulin

Anchorage-independent proliferation is a hallmark of oncogenic transformation and is thought to be conducive to proliferation of cancer cells away from their site of origin. We have previously reported that primary Schwann cells expressing the SV40 Large T antigen (LT) are not fully transformed in that they maintain a strict requirement for attachment, requiring a further genetic change, such as oncogenic Ras, to gain anchorage-independence. Using the LT-expressing cells, we performed a genetic screen for anchorage-independent proliferation and identified Sensory and Motor Neuron Derived Factor (SMDF), a transmembrane class III isoform of Neuregulin 1. In contrast to oncogenic Ras, SMDF induced enhanced proliferation in normal primary Schwann cells but did not trigger cellular senescence. In cooperation with LT, SMDF drove anchorage-independent proliferation, loss of contact inhibition and tumourigenicity. This transforming ability was shared with membrane-bound class III but not secreted class I isoforms of Neuregulin, indicating a distinct mechanism of action. Importantly, we show that despite being membrane-bound signalling molecules, class III neuregulins transform via a cell intrinsic mechanism, as a result of constitutive, elevated levels of ErbB signalling at high cell density and in anchorage-free conditions. This novel transforming mechanism may provide new targets for cancer therapy

Comparative genetic analysis: the utility of mouse genetic systems for studying human monogenic disease

One of the long-term goals of mutagenesis programs in the mouse has been to generate mutant lines to facilitate the functional study of every mammalian gene. With a combination of complementary genetic approaches and advances in technology, this aim is slowly becoming a reality. One of the most important features of this strategy is the ability to identify and compare a number of mutations in the same gene, an allelic series. With the advent of gene-driven screening of mutant archives, the search for a specific series of interest is now a practical option. This review focuses on the analysis of multiple mutations from chemical mutagenesis projects in a wide variety of genes and the valuable functional information that has been obtained from these studies. Although gene knockouts and transgenics will continue to be an important resource to ascertain gene function, with a significant proportion of human diseases caused by point mutations, identifying an allelic series is becoming an equally efficient route to generating clinically relevant and functionally important mouse models

The glial growth factors deficiency and synaptic destabilization hypothesis of schizophrenia

BACKGROUND: A systems approach to understanding the etiology of schizophrenia requires a theory which is able to integrate genetic as well as neurodevelopmental factors. PRESENTATION OF THE HYPOTHESIS: Based on a co-localization of loci approach and a large amount of circumstantial evidence, we here propose that a functional deficiency of glial growth factors and of growth factors produced by glial cells are among the distal causes in the genotype-to-phenotype chain leading to the development of schizophrenia. These factors include neuregulin, insulin-like growth factor I, insulin, epidermal growth factor, neurotrophic growth factors, erbB receptors, phosphatidylinositol-3 kinase, growth arrest specific genes, neuritin, tumor necrosis factor alpha, glutamate, NMDA and cholinergic receptors. A genetically and epigenetically determined low baseline of glial growth factor signaling and synaptic strength is expected to increase the vulnerability for additional reductions (e.g., by viruses such as HHV-6 and JC virus infecting glial cells). This should lead to a weakening of the positive feedback loop between the presynaptic neuron and its targets, and below a certain threshold to synaptic destabilization and schizophrenia. TESTING THE HYPOTHESIS: Supported by informed conjectures and empirical facts, the hypothesis makes an attractive case for a large number of further investigations. IMPLICATIONS OF THE HYPOTHESIS: The hypothesis suggests glial cells as the locus of the genes-environment interactions in schizophrenia, with glial asthenia as an important factor for the genetic liability to the disorder, and an increase of prolactin and/or insulin as possible working mechanisms of traditional and atypical neuroleptic treatments

Surface engineering of gallium arsenide with 4-mercaptobiphenyl monolayers

In this study, we propose a new method for engineering of stoichiometric GaAs [100] surfaces with self-assembled monolayers of 4-mercaptobiphenyl. In the first part, surface homogeneity and topography were studied by contact angle measurements and atomic force microscopy (AFM), where it was concluded that grafting of mercaptobiphenyl layers did not increase surface roughness. Thickness of the biphenyl layer was measured by ellipsometry, 10 ± 2 Å, suggesting that the surface was coated with a monolayer. After grafting, ellipsometric angles were stable for more than a week, which confirmed chemical stability of the coated surface in air. In the second part, electrochemical properties of GaAs with biphenyl monolayers were studied. Cyclic voltammograms revealed a significant suppression of electrochemistry by deposition of electrically insulating biphenyl monolayers. Indeed, impedance spectra measured at a cathodic potential (−350 mV) demonstrated that the interface resistance was remarkably increased by a factor of 50. Furthermore, both interface resistance (3.2 MΩ cm2) and capacitance (0.45 μF cm-2) of the coated GaAs electrodes were stable for 22 h. Chemical modification of GaAs surfaces with mercaptobiphenyl monolayers as established here includes has a large potential toward for the flexible functionalization of GaAs-based semiconductor nanostructures with bio-organic molecular assemblies both in air and in aqueous electrolytes

Chemical engineering of gallium arsenide surfaces with 4‘-methyl-4-mercaptobiphenyl and 4‘-hydroxy-4-mercaptobiphenyl monolayers

Stable chemical engineering of stoichiometric GaAs [100] surfaces was achieved by deposition of two types of mercaptobiphenyls: 4‘-methyl-4-mercaptobiphenyl and 4‘-hydroxy-4-mercaptobiphenyl, which can render the surface hydrophobic and hydrophilic, respectively. Topography of the engineered surface was studied by atomic force microscopy (AFM), and the covalent binding between the thiolate and surface arsenide was confirmed by high-resolution X-ray photoelectron spectroscopy (HRXPS). Total surface free energies of the engineered surfaces as well as its dispersive and polar components were calculated from contact angle measurements. Electrochemical properties of the engineered GaAs in aqueous electrolytes were measured by impedance spectroscopy at a cathodic potential (−350 mV), demonstrating that both types of mercaptobiphenyls can form stable monolayers with high electric resistances, R > 2 MΩ cm2. The surface engineering method established here allows for control of surface free energies toward deposition of model biomembranes on GaAs-based device surfaces

Spectroscopic characterization of 4‘-substituted aromatic self-assembled monolayers on GaAs(100) surface

High-resolution X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy were applied to characterize GaAs(100) surface engineered by self-assembled monolayers (SAMs) of 4‘-substituted aromatic molecules:  4‘-methyl-4-mercaptobiphenyl (CH3−BPT) and 4‘-hydroxy-4-mercaptobiphenyl (OH−BPT). Both of these molecules formed ordered and densely packed SAMs on GaAs, which were able to protect the substrate from degradation under ambient conditions. The molecular attachment in the SAMs is mediated by As-thiolate bond while the intact aromatic backbones have an upright orientation with average tilt angles of 31.0° and 37.2° for CH3−BPT and OH−BPT films, respectively. The difference in the tilt angle is attributed to a higher (by 7−10%) packing density of the former SAM, suggesting that the character of 4‘-substitution affects the quality of the resulting SAM on the GaAs substrate