Salinity adaptation of the invasive New Zealand mud snail (Potamopyrgus antipodarum) in the Columbia River estuary (Pacific Northwest, USA): physiological and molecular studies

In this study, we examine salinity stress tolerances of two populations of the invasive species New Zealand mud snail Potamopyrgus antipodarum, one population from a high salinity environment in the Columbia River estuary and the other from a fresh water lake. In 1996, New Zealand mud snails were discovered in the tidal reaches of the Columbia River estuary that is routinely exposed to salinity at near full seawater concentrations. In contrast, in their native habitat and throughout its spread in the western US, New Zealand mud snails are found only in fresh water ecosystems. Our aim was to determine whether the Columbia River snails have become salt water adapted. Using a modification of the standard amphipod sediment toxicity test, salinity tolerance was tested using a range of concentrations up to undiluted seawater, and the snails were sampled for mortality at daily time points. Our results show that the Columbia River snails were more tolerant of acute salinity stress with the LC₅₀ values averaging 38 and 22 Practical Salinity Units for the Columbia River and freshwater snails, respectively. DNA sequence analysis and morphological comparisons of individuals representing each population indicate that they were all P. antipodarum. These results suggest that this species is salt water adaptable and in addition, this investigation helps elucidate the potential of this aquatic invasive organism to adapt to adverse environmental conditions.     

Integrin-type fibronectin receptors of rat arterial smooth muscle cells: isolation, partial characterization and role in cytoskeletal organization and control of differentiated properties

The spreading of freshly isolated rat arterial smooth muscle cells (SMCs) on a substrate of fibronectin (FN) is associated with marked changes in fine structure and function of the cells, collectively referred to as a modulation from a contractile to a synthetic phenotype. Recent studies have indicated that this process is mediated via an interaction between the minimal cell-attachment sequence of FN (RGDS) and cell surface receptors. Here, we report the isolation of such receptors by sequential chromatography on affinity columns of wheat germ agglutinin (WGA) and a 105-kDa cell-binding fragment of FN (105-kDa fragment). The receptor was composed of two proteins with electrophoretic mobilities in SDS-polyacrylamide gels of 160 and 115 kDa under nonreducing conditions and 150 and 130 kDa under reducing conditions. Immunoprecipitation of surface-labeled cells with a rabbit antiserum against the beta chain of the rat hepatocyte FN receptor similarly yielded two proteins of 160 and 115 kDa. In metabolically labeled cells an additional component of 105 kDa was precipitated, presumably representing a precursor of the 115-kDa protein. Immunocytochemical studies demonstrated that SMCs grown on laminin formed FN fibrils and actin filament bundles in close alignment with cell surface receptors after a few days of culture. In cells seeded on the 105-kDa fragment, the receptors were already arranged in parallel with actin filaments on the first day of culture. Later on, the cells secreted FN and laid down FN fibrils along the receptors on the cell surface and the actin filament bundles in the cytoplasm. Taken together, the findings indicate that arterial SMCs are equipped with FN receptors that belong to the integrin family of proteins and consists of alpha (160-kDa) and beta (115-kDa) subunits. The receptor complexes apparently play an important role in determining the differentiated characteristics of the cells, possibly by mediating a linkage between the extracellular matrix and the cytoskeleton.     

E-pharmacophore filtering and molecular dynamics simulation studies in the discovery of potent drug-like molecules for chronic kidney disease

Chronic kidney disease (CKD) is a prominent health issue reported globally. The level of the vitamin D receptor (VDR) and cytochrome P450 enzyme 24-hydroxylase (CYP24A1) are crucial in the pathogenesis of secondary hyperparathyroidism (sHPT) in CKD. An elevated expression of the CYP24A1 leads to the deficiency of vitamin D and resistance to vitamin D therapy. Hence, VDR agonists and CYP24A1 antagonists are suggested to CKD patients for the management of biochemical complications. CTA-018 is a recently reported analog and acts as a potent CYP24A1 inhibitor. It inhibits CYP24A1 with an IC₅₀ 27 ± 6 nM, about 10 times more potentially than the non-selective inhibitor ketoconazole (253 ± 20 nM), and it is also been reported to induce the VDR expression. Thus, CTA-018 is under clinical trial among CKD patients. In this study, combined molecular docking and pharmacophore filtering were employed to identify compounds better than CTA-018. A huge set of 9127 compounds from Sweet Lead database were docked into the active site of VDR using Glide XP program. E-pharmacophore was developed from both the targets along with CTA-018. The compounds retrieved from the two different pharmacophore-based screening were re-docked into the active site of CYP24A1. The hits that bind well at both the active sites and matched with the pharmacophore models were considered as possible dual functional molecules against VDR and CYP24A1. Further, molecular dynamics simulation and subsequent energy decomposition analyses were also performed to study the role of specific amino acids in the active site of both VDR and CYP24A1.     

Effects of dimethyl sulfoxide on the globally ischemic heart: Possible general relevance to hypothermic organ preservation

Isolated perfused rabbit hearts were made globally ischemic for 2 hr, then reperfused. For 5 min before and after ischemia hearts were perfused with hypothermic (20 or 27 °C), hypoxic, substrate-free cardioplegic solutions, some of which contained 70 mM dimethyl sulfoxide. Postischemic ventricular pressure development, spontaneous heart rate, coronary flow, lactate dehydrogenase release, tissue Ca²⁺ content, and in vitro mitochondrial oxidative phosphorylation were used to evaluate the protective effects of the various solutions. Aside from the expected observations that cold cardioplegia lessens ischemic damage, we found that dimethyl sulfoxide gave no indication that it exacerbated ischemic damage or lessened the protection afforded by cardioplegia. We also found that, compared to values measured in comparable drug-free treated hearts, dimethyl sulfoxide significantly improved mitochondrial State 3 respiratory rates, respiratory control, and oxidative phosphorylation rates, and essentially prevented mitochondrial changes due to ischemia and reperfusion. We propose that dimethyl sulfoxide may act as a “scavenger” of cytotoxic free radicals, many of which are known to be generated by mitochondria during reoxygenation. Since hypoxia, ischemia, and reoxygenation are common accompaniments of most organ preservation protocols, we suggest that low concentrations of dimethyl sulfoxide might serve as a useful adjunct to organ preservation in the nonfrozen state, when cryoprotective concentrations are not needed.     

Taxonomic identity determines N2 fixation by canopy trees across lowland tropical forests

Legumes capable of fixing atmospheric N₂ are abundant and diverse in many tropical forests, but the factors determining ecological patterns in fixation are unresolved. A long‐standing idea is that fixation depends on soil nutrients (N, P or Mo), but recent evidence shows that fixation may also differ among N₂‐fixing species. We sampled canopy‐height trees across five species and one species group of N₂‐fixers along a landscape P gradient, and manipulated P and Mo to seedlings in a shadehouse. Our results identify taxonomy as the major determinant of fixation, with P (and possibly Mo) only influencing fixation following tree‐fall disturbances. While 44% of trees did not fix N₂, other trees fixed at high rates, with two species functioning as superfixers across the landscape. Our results raise the possibility that fixation is determined by biodiversity, evolutionary history and species–specific traits (tree growth rate, canopy stature and response to disturbance) in the tropical biome.     

Evolution of karyotype,sex chromosomes,and meiosis in mygalomorph spiders (Araneae: Mygalomorphae)

Spider diversity is partitioned into three primary clades, namely Mesothelae, Mygalomorphae, and Araneomorphae. Mygalomorph cytogenetics is largely unknown. Our study revealed a remarkable karyotype diversity of mygalomorphs. Unlike araneomorphs, they show no general trend towards a decrease of 2n, as the chromosome number was reduced in some lineages and increased in others. A biarmed karyotype is a symplesiomorphy of mygalomorphs and araneomorphs. Male meiosis of some mygalomorphs is achiasmatic, or includes the diffuse stage. The sex chromosome system X₁X₂0, which is supposedly ancestral in spiders, is uncommon in mygalomorphs. Many mygalomorphs exhibit more than two (and up to 13) X chromosomes in males. The evolution of X chromosomes proceeded via the duplication of chromosomes, fissions, X–X, and X‐autosome fusions. Spiders also exhibit a homomorphic sex chromosome pair. In the germline of mygalomorph males these chromosomes are often deactivated; their deactivation and pairing is initiated already at spermatogonia. Remarkably, pairing of sex chromosomes in mygalomorph females is also initiated at gonial cells. Some mygalomorphs have two sex chromosome pairs. The second pair presumably arose in early‐diverging mygalomorphs, probably via genome duplication. The unique behaviour of spider sex chromosomes in the germline may promote meiotic pairing of homologous sex chromosomes and structural differentiation of their duplicates, as well as the establishment of polyploid genomes. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 377–408.