Zinc finger domain of the human DTX protein adopts a unique RING fold

The Deltex (DTX) family is involved in ubiquitination and acts as Notch signaling modifiers for controlling cell fate determination. DTX promotes the development of the ubiquitin chain via its RING finger (DTX_RING). In this study, the solution structure of DTX_RING was determined using nuclear magnetic resonance (NMR). Moreover, by experiments with a metallochromic indicator, we spectrophotometrically estimated the stoichiometry of zinc ions and found that DTX_RING possesses zinc‐binding capabilities. The Simple Modular Architecture Research Tool database predicted the structure of DTX_RING as a typical RING finger. However, the actual DTX_RING structure adopts a novel RING fold with a unique topology distinct from other RING fingers. We unveiled the position and the range of the DTX_RING active site at the atomic level. Artificial RING fingers (ARFs) are made by grafting active sites of the RING fingers onto cross‐brace structure motifs. Therefore, the present structural analysis could be useful for designing a novel ARF.     

Asian tiger mosquitos (Aedes albopictus) in urban Tokyo,Japan show low cytochrome c oxidase subunit 1 diversity

The Asian tiger mosquito, Aedes albopictus, is a common mosquito in East and Southeast Asia, but its habitats have expanded to the American, African and Australian continents, Europe and many other areas. Aedes albopictus can transmit some important arboviruses that cause human mortality. To control the global spread of this mosquito, genetic analyses of A. albopictus populations have been undertaken throughout the world. In Japan, however, few attempts have been made to characterize the population structures of these mosquitos. In this study, adult A. albopictus populations were sampled from seven parks in the urban area of Tokyo, and analyses of the mitochondrial cytochrome c oxidase subunit 1 (COI) gene base sequences revealed small genetic variations. Only three haplotypes were identified, and most of the samples belonged to a single haplotype. In addition, despite a developed international trade network, no establishment of A. albopictus populations from multiple origins was found. We also evaluated the genetic diversity outside Tokyo using data from a previous study for comparison and found that the genetic diversity in the urban area of Tokyo was lower than that in Nagasaki City (Japan) and in other countries, including the USA and Italy, where A. albopictus populations from Japan have been established.     

An alien Sennertia mite (Acari: Chaetodactylidae) associated with an introduced Oriental bamboo‐nesting large carpenter bee (Hymenoptera: Apidae: Xylocopa) invading the central Honshu Island,Japan

Since 2006, an introduced Oriental bamboo‐nesting large carpenter bee, Xylocopa tranquebarorum, has been recorded from the central Honshu Island, Japan, which is inhabited only by the endemic subspecies, Xylocopa appendiculata circumvolans. Carpenter bees (tribes Xylocopini and Ceratinini) have ecological associations with specific Sennertia spp. in all geographic regions of their distribution, thus it is worried that the introduced carpenter bee has brought non‐indigenous mites into Japan. In their native ranges, X. a. circumvolans and X. tranquebarorum each has specific Sennertia mite faunas: the four Japanese Alloxylocopa bees including X. a. circumvolans have associations with S. alfkeni, while X. tranquebarorum has association with S. potanini in China (except Taiwan) and with S. horrida in South to East Asia including Taiwan. In the present study, we examined phoretic mite fauna on the introduced X. tranquebarorum, and determined whether the mites are indigenous or not based on morphological character and two gene sequences (mitochondrial cytochrome oxidase subunit I gene and nuclear ribosomal internal transcribed spacer). It was found from the result of this study that the non‐indigenous Sennertia mite has invaded Japan with the introduced X. tranquebarorum. We discuss geographic origin of the introduced X. tranquebarorum based on associated mite fauna and potential ecological risk caused by the introduced Xylocopa‐Sennertia association.     

A liver-derived secretory protein, selenoprotein P, causes insulin resistance

The liver may regulate glucose homeostasis by modulating the sensitivity/resistance of peripheral tissues to insulin, by way of the production of secretory proteins, termed hepatokines. Here, we demonstrate that selenoprotein P (SeP), a liver-derived secretory protein, causes insulin resistance. Using serial analysis of gene expression (SAGE) and DNA chip methods, we found that hepatic SeP mRNA levels correlated with insulin resistance in humans. Administration of purified SeP impaired insulin signaling and dysregulated glucose metabolism in both hepatocytes and myocytes. Conversely, both genetic deletion and RNA interference-mediated knockdown of SeP improved systemic insulin sensitivity and glucose tolerance in mice. The metabolic actions of SeP were mediated, at least partly, by inactivation of adenosine monophosphate-activated protein kinase (AMPK). In summary, these results demonstrate a role of SeP in the regulation of glucose metabolism and insulin sensitivity and suggest that SeP may be a therapeutic target for type 2 diabetes.     

Sex Reversal in Zebrafish fancl Mutants Is Caused by Tp53-Mediated Germ Cell Apoptosis

The molecular genetic mechanisms of sex determination are not known for most vertebrates, including zebrafish. We identified a mutation in the zebrafish fancl gene that causes homozygous mutants to develop as fertile males due to female-to-male sex reversal. Fancl is a member of the Fanconi Anemia/BRCA DNA repair pathway. Experiments showed that zebrafish fancl was expressed in developing germ cells in bipotential gonads at the critical time of sexual fate determination. Caspase-3 immunoassays revealed increased germ cell apoptosis in fancl mutants that compromised oocyte survival. In the absence of oocytes surviving through meiosis, somatic cells of mutant gonads did not maintain expression of the ovary gene cyp19a1a and did not down-regulate expression of the early testis gene amh; consequently, gonads masculinized and became testes. Remarkably, results showed that the introduction of a tp53 (p53) mutation into fancl mutants rescued the sex-reversal phenotype by reducing germ cell apoptosis and, thus, allowed fancl mutants to become fertile females. Our results show that Fancl function is not essential for spermatogonia and oogonia to become sperm or mature oocytes, but instead suggest that Fancl function is involved in the survival of developing oocytes through meiosis. This work reveals that Tp53-mediated germ cell apoptosis induces sex reversal after the mutation of a DNA–repair pathway gene by compromising the survival of oocytes and suggests the existence of an oocyte-derived signal that biases gonad fate towards the female developmental pathway and thereby controls zebrafish sex determination.     

Cadherin-mediated Intercellular Adhesion and Signaling Cascades Involving Small GTPases

Epithelia form physical barriers that separate the internal milieu of the body from its external environment. The biogenesis of functional epithelia requires the precise coordination of many cellular processes. One of the key events in epithelial biogenesis is the establishment of cadherin-dependent cell–cell contacts, which initiate morphological changes and the formation of other adhesive structures. Cadherin-mediated adhesions generate intracellular signals that control cytoskeletal reorganization, polarity, and vesicle trafficking. Among such signaling pathways, those involving small GTPases play critical roles in epithelial biogenesis. Assembly of E-cadherin activates several small GTPases and, in turn, the activated small GTPases control the effects of E-cadherin-mediated adhesions on epithelial biogenesis. Here, we focus on small GTPase signaling at E-cadherin-mediated epithelial junctions.Cell–cell adhesions are involved in a diverse range of physiological processes, including morphological changes during tissue development, cell scattering, wound healing, and synaptogenesis (Adams and Nelson 1998; Gumbiner 2000; Halbleib and Nelson 2006; Takeichi 1995; Tepass et al. 2000). In epithelial cells, cell–cell adhesions are classified into three kinds of adhesions: adherens junction, tight junction, and desmosome (for more details, see Meng and Takeichi 2009, Furuse 2009, and Delva et al. 2009, respectively). A key event in epithelial polarization and biogenesis is the establishment of cadherin-dependent cell–cell contacts. Cadherins belong to a large family of adhesion molecules that require Ca²⁺ for their homophilic interactions (Adams and Nelson 1998; Blanpain and Fuchs 2009; Gumbiner 2000; Hartsock and Nelson 2008; Takeichi 1995; Tepass et al. 2000). Cadherins form transinteraction on the surface of neighboring cells (for details, see Shapiro and Weis 2009). For the development of strong and rigid adhesions, cadherins are clustered concomitantly with changes in the organization of the actin cytoskeleton (Tsukita et al. 1992). Classical cadherins are required, but not sufficient, to initiate cell–cell contacts, and other adhesion protein complexes subsequently assemble (for details, see Green et al. 2009). These complexes include the tight junction, which controls paracellular permeability, and desmosomes, which support the structural continuum of epithelial cells. A fundamental problem is to understand how these diverse cellular processes are regulated and coordinated. Intracellular signals, generated when cells attach with one another, mediate these complicated processes.Several signaling pathways upstream or downstream of cadherin-mediated cell–cell adhesions have been identified (Perez-Moreno et al. 2003) (see also McCrea et al. 2009). Among these pathways, small GTPases including the Rho and Ras family GTPases play critical roles in epithelial biogenesis and have been studied extensively. Many key morphological and functional changes are induced when these small GTPases act at epithelial junctions, where they mediate an interplay between cell–cell adhesion molecules and fundamental cellular processes including cytoskeletal activity, polarity, and vesicle trafficking. In addition to these small GTPases, Ca²⁺ signaling and phosphorylation of cadherin complexes also play pivotal roles in the formation and maintenance of cadherin-mediated adhesions. Here, we focus on signaling pathways involving the small GTPases in E-cadherin-mediated cell–cell adhesions. Other signaling pathways are described in recent reviews (Braga 2002; Fukata and Kaibuchi 2001; Goldstein and Macara 2007; McLachlan et al. 2007; Tsukita et al. 2008; Yap and Kovacs 2003; see also McCrea et al. 2009).     

Multiple processing forms and their biological activities of a novel angiogenesis inhibitor vasohibin

Vasohibin is a newly identified negative feedback regulator for angiogenesis. When expressed in cultured human endothelial cells, vasohibin polypeptides were detected in multiple distinct molecular weight forms, suggesting that some proteolytic events may occur within cells or the pericellular milieu. In order to identify the proteolysis sites, vasohibin cDNA mutants were generated to substitute some basic amino acids with alanine and then were transfected into endothelial cells. Western blots with anti-vasohibin monoclonal antibody following the transfection showed that there were at least two cleaving sites in the amino terminal region. Purified recombinant protein of the amino terminal truncated forms not only retained its inhibitory activity on angiogenesis in mouse corneal assay but also showed strong affinity to heparin. Moreover, deletion of some basic residues at the carboxyl terminal resulted in abrogation of both antiangiogenic and heparin-binding activities. Processing patterns and biological activities of the processed forms of this novel antiangiogenic factor are discussed.