Tissue-specific gene silencing by RNA interference in the whitefly Bemisia tabaci (Gennadius)

The hemipteran whitefly Bemisia tabaci (Gennadius) species complex and the plant viruses they transmit pose major constraints to vegetable and fiber production, worldwide. The whitefly tissue- and developmental-specific gene expression has not been exhaustively studied despite its economic importance. In 2002, a functional genomic project was initiated, which generated several thousands expressed sequence tags (ESTs) and their sequence. This project provides the basic information to design experiments aimed at understanding and manipulating whitefly gene expression. In this communication, for the first time we provide evidence that the RNA interference mechanism discovered in many organisms, including in Hemiptera, is active in B. tabaci. By injecting into the body cavity long double-stranded RNA (dsRNA) molecules, specifically directed against genes uniquely expressed in the midgut and salivary glands, we were able to significantly inhibit the expression of the targeted mRNA in the different organs. Gene expression levels in RNAi-silenced whiteflies were reduced up to 70% compared to whiteflies injected with buffer or with a green fluorescent protein (GFP)-specific dsRNA. Phenotypic effects were observed in B. tabaci ovaries following dsRNA targeting the whitefly Drosophila chickadee homologue. Disruption of whitefly gene expression opens the door to new strategies aimed at curbing down the deleterious effects of this insect pest to agriculture.     

Co-infection and localization of secondary symbionts in two whitefly species

Background  

Whiteflies are cosmopolitan phloem-feeding pests that cause serious damage to many crops worldwide due to direct feeding and vectoring of many plant viruses. The sweetpotato whitefly Bemisia tabaci (Gennadius) and the greenhouse whitefly Trialeurodes vaporariorum (Westwood) are two of the most widespread and damaging whitefly species. To complete their unbalanced diet, whiteflies harbor the obligatory bacterium Portiera aleyrodidarum. B. tabaci further harbors a diverse array of secondary symbionts, including Hamiltonella, Arsenophonus, Cardinium, Wolbachia, Rickettsia and Fritschea. T. vaporariorum is only known to harbor P. aleyrodidarum and Arsenophonus. We conducted a study to survey the distribution of whitefly species in Croatia, their infection status by secondary symbionts, and the spatial distribution of these symbionts in the developmental stages of the two whitefly species.     

Nuclear DNA content of the whitefly Bemisia tabaci (Aleyrodidae: Hemiptera) estimated by flow cytometry

The nuclear DNA content of the whitefly Bemisia tabaci (Gennnadius) was estimated using flow cytometry. Male and female nuclei were stained with propidium iodide and their DNA content was estimated using chicken red blood cells and Arabidopsis thaliana L. (Brassicaceae) as external standards. The estimated nuclear DNA content of male and female B. tabaci was 1.04 and 2.06 pg, respectively. These results corroborated previous reports based on chromosome counting, which showed that B. tabaci males are haploid and females are diploid. Conversion between DNA content and genome size (1 pg DNA=980 Mbp) indicate that the haploid genome size of B. tabaci is 1020 Mbp, which is approximately five times the size of the genome of the fruitfly Drosophila melanogaster Meigen. These results provide an important baseline that will facilitate genomics-based research for the B. tabaci complex.     

Modeling the statistics of elementary calcium release events

Elementary Ca(2+) signals, such as "Ca(2+) puffs", which arise from the release of Ca(2+) from endoplasmic reticulum through small clusters of inositol 1,4,5-trisphosphate receptors, are the building blocks for intracellular Ca(2+) signaling. The small number of release channels involved during a Ca(2+) puff renders the puffs stochastic, with distributed amplitudes, durations, and frequency, well characterized experimentally. We present a stochastic model that accurately describes simultaneously the statistical properties of the duration, amplitudes, frequencies, and spatial spread with a single set of parameters.     

Adhesion of intermediate filaments and lipid droplets in adrenal cells studied by field emission scanning electron microscopy

High-resolution field emission scanning electron microscopy was used to study the organisation of intermediate filaments around lipid droplets and their binding to these droplets, in primary culture of bovine adrenal cells. Whole-mount preparations of intermediate filaments and bound lipid droplets were prepared from cells grown on Formvar-coated grids and processed by freeze-drying. Intermediate filaments were seen as an interconnected network enveloping the entire droplet. The bound filaments appear to be directly adherent to the surface of the droplet and hence take on its curved contour. The binding of the filaments to the droplets was determined by means of tilting. This study provides a new approach to investigate the cytoskeleton and its associated structures with high-resolution three-dimensional images.     

Large extracellular space leads to neuronal susceptibility to ischemic injury in a Na<Superscript>+</Superscript>/<Emphasis Type=Bold>K</Emphasis><Superscript>+</Superscript> pumps–dependent manner

The extent of anoxic depolarization (AD), the initial electrophysiological event during ischemia, determines the degree of brain region–specific neuronal damage. Neurons in higher brain regions exhibiting nonreversible, strong AD are more susceptible to ischemic injury as compared to cells in lower brain regions that exhibit reversible, weak AD. While the contrasting ADs in different brain regions in response to oxygen–glucose deprivation (OGD) is well established, the mechanism leading to such differences is not clear. Here we use computational modeling to elucidate the mechanism behind the brain region–specific recovery from AD. Our extended Hodgkin–Huxley (HH) framework consisting of neural spiking dynamics, processes of ion accumulation, and ion homeostatic mechanisms unveils that glial–vascular K⁺ clearance and Na⁺/K⁺–exchange pumps are key to the cell’s recovery from AD. Our phase space analysis reveals that the large extracellular space in the upper brain regions leads to impaired Na⁺/K⁺–exchange pumps so that they function at lower than normal capacity and are unable to bring the cell out of AD after oxygen and glucose is restored.     

High‐mobility group box‐1 induces vascular remodelling processes via c‐Jun activation

Extracellular high‐mobility group box‐1 (HMGB1) acts as a signalling molecule during inflammation, cell differentiation and angiogenesis. Increased abundance of HMGB1 is associated with several pathological disorders such as cancer, asthma and chronic obstructive pulmonary disease (COPD). In this study, we investigated the relevance of HMGB1 in the pathological remodelling present in patients with idiopathic pulmonary arterial hypertension (IPAH) and pulmonary hypertension (PH) associated with COPD. Remodelled vessels present in COPD with PH and IPAH lung samples were often surrounded by HMGB1‐positive cells. Increased HMGB1 serum levels were detected in both patient populations compared to control samples. The effects of physiological HMGB1 concentrations were then examined on cellular responses in vitro. HMGB1 enhanced proliferation of pulmonary arterial smooth muscle cells (PASMC) and primary human arterial endothelial cells (PAEC). HMGB1 stimulated p38, extracellular signal‐regulated kinase (ERK) and c‐Jun N‐terminal kinase (JNK) phosphorylation. Furthermore, activation of the downstream AP‐1 complex proteins c‐Fos and c‐Jun was observed. Silencing of c‐Jun ablated the HMGB1‐induced proliferation in PASMC. Thus, an inflammatory component such as HMGB1 can contribute to PASMC and PAEC proliferation and therefore potentially to vascular remodelling and PH pathogenesis.     

Mechanism and regulation of P element transposition

P elements were first discovered in the fruit fly Drosophila melanogaster as the causative agents of a syndrome of aberrant genetic traits called hybrid dysgenesis. This occurs when P element-carrying males mate with females that lack P elements and results in progeny displaying sterility, mutations and chromosomal rearrangements. Since then numerous genetic, developmental, biochemical and structural studies have culminated in a deep understanding of P element transposition: from the cellular regulation and repression of transposition to the mechanistic details of the transposase nucleoprotein complex. Recent studies have revealed how piwi-interacting small RNA pathways can act to control splicing of the P element pre-mRNA to modulate transposase production in the germline. A recent cryo-electron microscopy structure of the P element transpososome reveals an unusual DNA architecture at the transposon termini and shows that the bound GTP cofactor functions to position the transposon ends within the transposase active site. Genome sequencing efforts have shown that there are P element transposase-homologous genes (called THAP9) in other animal genomes, including humans. This review highlights recent and previous studies, which together have led to new insights, and surveys our current understanding of the biology, biochemistry, mechanism and regulation of P element transposition.