Viruses in the families Arteriviridae and Coronaviridae have enveloped virions which contain nonseg-mented, positive-stranded RNA, but the constituent genera differ markedly in genetic complexity and virion structure. Nevertheless, there are striking resemblances among the viruses in the organization and expression of their genomes, and sequence conservation among the polymerase polyproteins strongly suggests that they have a common ancestry. On this basis, the International Committee on Taxonomy of Viruses recently established a new order, Nidovirales, to contain the two families. Here, the common traits and distinguishing features of the Nidovirales are reviewed. r 1997 Academic Press KEY WORDS: arterivirus; coronavirus; torovirus; polyprotein processing; RNA recombination.

There is an urgent need for the development of new antifungal agents. A facile in vivo model that evaluates libraries of chemical compounds could solve some of the main obstacles in current antifungal discovery. We show that Candida albicans, as well as other Candida species, are ingested by Caenorhabditis elegans and establish a persistent lethal infection in the C. elegans intestinal track. Importantly, key components of Candida pathogenesis in mammals, such as filament formation, are also involved in nematode killing. We devised a Candida-mediated C. elegans assay that allows high-throughput in vivo screening of chemical libraries for antifungal activities, while synchronously screening against toxic compounds. The assay is performed in liquid media using standard 96-well plate technology and allows the study of C. albicans in non-planktonic form. A screen of 1,266 compounds with known pharmaceutical activities identified 15 (;1.2%) that prolonged survival of C. albicans-infected nematodes and inhibited in vivo filamentation of C. albicans. Two compounds identified in the screen, caffeic acid phenethyl ester, a major active component of honeybee propolis, and the fluoroquinolone agent enoxacin exhibited antifungal activity in a murine model of candidiasis. The wholeanimal C. elegans assay may help to study the molecular basis of C. albicans pathogenesis and identify antifungal compounds that most likely would not be identified by in vitro screens that target fungal growth. Compounds identified in the screen that affect the virulence of Candida in vivo can potentially be used as ‘‘probe compounds’ ’ and

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are generated from a single cell is a central question of devel-posterior pole and cortical material flows in the opposite MEX-3 appear associated with P granules and become asym-pinches off a cytoplasmic bridge to the syncytial germline at tive anterior is fertilised. After fer-olar bodies mmetries in been identi-axis speci-ll, 1990). identifyingdirection (Nigon et al., 1960; Hird and White, 1993). In concert with these movements, cytoplasmic P granules are segregated to the posterior (Strome and Wood, 1982, 1983) and foci of F-actin in the cortex become concentrated in the anterior (Strome, 1986b). Imaging live embryos has revealed that the P granules segregate to the posterior primarily by moving, rather than by being degraded en masse in the anterior (Hird et al., 1996), and there is evidence that cortical actin moves anteriorly at this time (Hird, 1996). approximately the same time, also at the presump pole. The oocyte then enters the spermatheca and at its leading edge, the presumptive posterior pole tilisation, the oocyte completes meiosis, releasing p at the presumptive anterior pole. Although no asy determinants or in cytoskeletal organisation have fied in the oocyte, such asymmetries play a role in fication in most other animals (for review see Wa In this paper, we describe experiments aimed atopmental biology. Caenorhabditis elegans is used as a model system for studying development, because of its potential for combining descriptive and experimental embryology, genetics, molecular biology and biochemistry. Although much is being learned about development in C. elegans, the source of initial asymmetry in its development has remained unknown. C. elegans has an obvious anteroposterior (AP) axis, with distinct structures at distinct positions along the body. The axis appears to be determined very early in development, before first cleavage, as asymmetries of critical regulatory proteins arise by this time. A cytoplasmic rearrangement during the first cell cycle has been implicated in establishing some asymme-tries. In a 5-10 minute interval found to be critical for gener-ating certain cellular and developmental asymmetries (Hill and Strome, 1988, 1990), central cytoplasm flows toward the future

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ABSTRACT The vasa gene encodes an ATPdependent RNA helicase belonging to the DEAD-box family that, in many organisms, is specifically expressed in germline cells throughout the life cycle. In this study we first cloned Pacific white shrimp (Litopenaeus vannamei) partial cDNAs of two members of the DEAD-box family, one belonging to the vasa subfamily (Lv-Vasa) and the other to the PL10 subfamily (Lv-PL10). Examination of their spatial expression pattern in adult tissues revealed that Lv-Vasa is restricted to the gonads, whereas Lv-PL10 is found in gonads as well as in somatic tissues. Next, we cloned the full-length shrimp vasa cDNA and found that Lv-Vasa encoded a protein with a DEAD-like helicase domain followed by a helicase superfamily C-terminal domain. In addition, Lv-Vasa encoded N-terminal three repeats of the C2HC-type zinc finger domain, a motif encoded by vasa genes of several crustaceans and several other invertebrate organisms. In situ hybridization of ovarian sections showed that the Lv-Vasa transcript is localized to the cytoplasm of the oocyte throughout oogenesis. The abundance of Lv-Vasa mRNA in mature oocytes suggests a maternal contribution for the developing embryo. It is demonstrated that the vasa homolog from L. vannamei is a gonad specific germline cell marker that could be exploited to enhance our understanding of developmental and reproductive processes in the germline of this economically important shrimp. Mol. Reprod.

A Drosophila RNA helicase gene, pitchoune, is required for cell

Abstract: The vasa gene is a key determinant for germline formation in eukaryotes. This gene, highly conserved through evolution, encodes a RNA helicase protein member of the DEAD-box family. To understand the germline formation in oyster, we report here the isolation and the characterization of a vasa orthologue in Crassostrea gigas (Oyvlg). OyVLG contained the eight consensus domains of the DEAD-box including those providing RNA unwinding activity. The expression pattern of Oyvlg was examined in adult oyster tissues at different reproductive stages. Its expression was restricted to germline cells both in males and females, including germinal stem cells and auxiliary cells. The expression of Oyvlg, strongest in early germ cells, decreased as the maturation proceeded. These data and the evolutionary conservation observed suggested the role of Oyvlg in germline development. Oyvlg is the first germ cell specific marker in oyster and will be very useful in studies of oyster germline formation.

2. Course of germline proliferation................................................................................................. 3 3. Control of germline proliferation by Notch signaling and the somatic gonad....................................... 4 3.1. The DTC and Notch signaling promote germline stem cells................................................... 4

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