Transgenic mouse models for ADHD

Attention-deficit hyperactivity disorder (ADHD) is a developmental disorder characterized by symptoms of inattention, impulsivity and hyperactivity that adversely affect many aspects of life. Whereas the etiology of ADHD remains unknown, growing evidence indicates a genetic involvement in the development of this disorder. The brain circuits associated with ADHD are rich in monoamines, which are involved in the mechanism of action of psychostimulants and other medications used to treat this disorder. Dopamine (DA) is believed to play a major role in ADHD but other neurotransmitters are certainly also involved. Genetically modified mice have become an indispensable tool used to analyze the contribution of genetic factors in the pathogenesis of human disorders. Although rodent models cannot fully recapitulate complex human psychiatric disorders such as ADHD, transgenic mice offer an opportunity to directly investigate in vivo the specific roles of novel candidate genes identified in ADHD patients. Several knock-out and transgenic mouse models have been proposed as ADHD models, mostly based on targeting genes involved in DA transmission, including the gene encoding the dopamine transporter (DAT1). These mutant models provided an opportunity to evaluate the contribution of dopamine-related processes to brain pathology, to dissect the neuronal circuitry and molecular mechanisms involved in the antihyperkinetic action of psychostimulants and to evaluate novel treatments for ADHD. New transgenic models mouse models targeting other genes have recently been proposed for ADHD. Here, we discuss the recent advances and pitfalls in modeling ADHD endophenotypes in genetically altered animals.     

An evolutionary conserved pattern of 18S rRNA sequence complementarity to mRNA 5′ UTRs and its implications for eukaryotic gene translation regulation

There are several key mechanisms regulating eukaryotic gene expression at the level of protein synthesis. Interestingly, the least explored mechanisms of translational control are those that involve the translating ribosome per se, mediated for example via predicted interactions between the ribosomal RNAs (rRNAs) and mRNAs. Here, we took advantage of robustly growing large-scale data sets of mRNA sequences for numerous organisms, solved ribosomal structures and computational power to computationally explore the mRNA–rRNA complementarity that is statistically significant across the species. Our predictions reveal highly specific sequence complementarity of 18S rRNA sequences with mRNA 5′ untranslated regions (UTRs) forming a well-defined 3D pattern on the rRNA sequence of the 40S subunit. Broader evolutionary conservation of this pattern may imply that 5′ UTRs of eukaryotic mRNAs, which have already emerged from the mRNA-binding channel, may contact several complementary spots on 18S rRNA situated near the exit of the mRNA binding channel and on the middle-to-lower body of the solvent-exposed 40S ribosome including its left foot. We discuss physiological significance of this structurally conserved pattern and, in the context of previously published experimental results, propose that it modulates scanning of the 40S subunit through 5′ UTRs of mRNAs.     

In vitro catabolic effect of protoporphyrin IX in human osteoblast-like cells: possible role of the 18 kDa mitochondrial translocator protein

In several pathological conditions, when conversion of Protoporphyrin (PP)IX into heme is impaired, a toxic accumulation of PPIX might occur. PPIX has been found to have affinity to the mitochondrial Translocator Protein 18 kDa. Since it is known that TSPO is abundant in human osteoblast cells, thus we assumed that PPIX can affect cellular functions via interactions with TSPO in these cells. Therefore we aimed to study the metabolic responses of human osteoblast to a high (10^?5M) concentration of PPIX in vitro. We found that in primary culture of human osteoblast-like cells cell numbers decreased following exposure to PPIX(10^?5M). Cellular [¹⁸F]-FDG incorporation, mitochondrial mass, ATP content were suppressed, and ΔΨm collapsed. Lactate dehydrogenase activity was enhanced in culture media, indicating overall cell death, while no increase in apoptotic levels was observed. Cellular proliferation was not affected. Protein expression of TSPO, VDAC 1, and hexokinase 2 decreased, although the synthesis of mRNA for hexokinase 2 increased. Thus, PPIX(10^?5M) has a cytotoxic effect on human osteoblast-like cell in vitro. Since these cells remain viable following exposure to another TSPO ligand, PK 11195 (10^?5M), as observed previously by us, the mode of action of PPIX on osteoblast-like cells is not identical to that of PK 11195. Accordingly pathological accumulation of PPIX may cause necrosis of osteoblasts leading to bone mass loss. We show that this phenomenon is unrelated to iron overload.     

Comparative phylogeography of Australo‐Papuan mangrove‐restricted and mangrove‐associated avifaunas

The world's richest mangrove‐restricted avifauna is in Australia and New Guinea. The history of differentiation of the species involved and their patterns of intraspecific genetic variation remain poorly known. Here, we use sequence data derived from two mitochondrial protein‐coding genes to study the evolutionary history of eight co‐distributed mangrove‐restricted and mangrove‐associated birds from the Australian part of this region. Utilizing a comparative phylogeographical framework, we observed that the study species present concordantly located phylogeographical breaks across their shared geographical distribution, a plausible signature of common mechanisms of vicariance underlying this pattern. Barriers such as the Canning Gap, Bonaparte Gap, and the Carpentarian Gaps all had important but varying degrees of impact on the studied species. The Burdekin Gap along Australia's eastern seaboard probably had only a minor influence as a barrier to gene flow in mangrove birds. Statistical phylogeographical simulations were able to discriminate among alternative scenarios involving six different geographical and temporal population separations. Species exhibiting recent colonizations into mangroves include Rhipidura phasiana, Myiagra ruficollis, and Myzomela erythrocephala. By contrast, Peneoenanthe pulverulenta, Pachycephala melanura, Pachycephala lanioides, Zosterops luteus, and Colluricincla megarhyncha all had deeper histories, reflected as more marked phylogeographical divisions separating populations on the eastern seaboard/Cape York Peninsula from more western regions such as the Arnhem Land, the Pilbara, and the Kimberley. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 574–598.     

A thin‐walled polydimethylsiloxane bioreactor for high‐density hepatocyte sandwich culture

In vitro drug testing requires long‐term maintenance of hepatocyte liver specific functions. Hepatocytes cultured at a higher seeding density in a sandwich configuration exhibit an increased level of liver specific functions when compared to low density cultures due to the better cell to cell contacts that promote long term maintenance of polarity and liver specific functions. However, culturing hepatocytes at high seeding densities in a standard 24‐well plate poses problems in terms of the mass transport of nutrients and oxygen to the cells. In view of this drawback, we have developed a polydimethylsiloxane (PDMS) bioreactor that was able to maintain the long‐term liver specific functions of a hepatocyte sandwich culture at a high seeding density. The bioreactor was fabricated with PDMS, an oxygen permeable material, which allowed direct oxygenation and perfusion to take place simultaneously. The mass transport of oxygen and the level of shear stress acting on the cells were analyzed by computational fluid dynamics (CFD). The combination of both direct oxygenation and perfusion has a synergistic effect on the liver specific function of a high density hepatocyte sandwich culture over a period of 9 days. Biotechnol. Bioeng. 2013; 110: 1663–1673. © 2012 Wiley Periodicals, Inc.