Monitoring the invasion of the aquatic bug <Emphasis Type="Italic">Trichocorixa verticalis verticalis</Emphasis> (Hemiptera: Corixidae) in the wetlands of Doñana National Park (SW Spain)

We have detected the presence of the North American native corixid Trichocorixa verticalis verticalis (Fieber, 1851) in Doñana wetlands (SW Spain). We have collected data from different research projects done in the area during the period of 2001–2007. We have sampled 134 different sites in Doñana and we found the exotic corixid in 66 occasions. We have found two reproductive populations that might act as sources for the colonization of other waterbodies in the area. When reproduction occurred T. v. verticalis outcompeted native corixids. Its presence out of the waterbodies where we detected reproduction was in small numbers and probably due to vagrant individuals.     

Shell shape affects movement patterns and microhabitat distribution in the hermit crabs Calcinus elegans, C. laevimanus and C. latens

This study examined the influence of shell shape on the distribution and movement patterns of three species of Hawaiian hermit crabs: Calcinus elegans, C. laevimanus, and C. latens. Field surveys showed strong differences in shell use depending on habitat. Individuals of C.elegans and C. latens were more frequently in unusual shapes of shells (the cowrie Cypraea caputserpentis and the variable worm shell Serpulorbis variabilis) when in tide pools and in more standard gastropod shells, such as the dog whelk Nassarius papillosus, when found in the subtidal. In addition, for both C.elegans and C. latens in tide pools, most crabs in unusual shaped shells were out on top of rocks, whereas most crabs in shells that were standard shapes were under rocks.In the laboratory, individuals of C.elegans and C. laevimanus in unusual shells initiated more shell exchanges and when given empty shells crabs readily occupied the standard shaped shells, but crabs did not move into the unusual shaped shells. Mark-recapture experiments in the field showed that C. elegans in standard shaped shells moved out of tide pools and stayed longer when placed on subtidal coral heads, whereas crabs in unusual shaped shells stayed in tide pools and did not stay on subtidal coral heads (in part due to predation). Laboratory tests showed that C. elegans in unusual shaped shells were more readily dislodged by surge than crabs in standard shaped shells. Thus, the difference in movement patterns in preferred vs. unpreferred shell shapes is an important factor influencing the microhabitat distribution of these hermit crabs.     

Herb and conifer roots show similar high sensitivity to water deficit

Root systems play a major role in supplying the canopy with water, enabling photosynthesis and growth. Yet, much of the dynamic response of root hydraulics and its influence on gas exchange during soil drying and recovery remains uncertain. We examined the decline and recovery of the whole root hydraulic conductance (Kr) and canopy diffusive conductance (g_c) during exposure to moderate water stress in two species with contrasting root systems: Tanacetum cinerariifolium (herbaceous Asteraceae) and Callitris rhomboidea (woody conifer). Optical dendrometers were used to record stem water potential at high temporal resolution and enabled non-invasive measurements of Kr calculated from the rapid relaxation kinetics of water potential in hydrating roots. We observed parallel declines in Kr and g_c to <20% of unstressed levels during the early stages of water stress in both species. The recovery of Kr after rewatering differed between species. T. cinerariifolium recovered quickly, with 60% of Kr recovered within 2 h, while C. rhomboidea was much slower to return to its original Kr. Recovery of g_c followed a similar trend to Kr in both species, with C. rhomboidea slower to recover. Our findings suggest that the pronounced sensitivity of Kr to drought is a common feature among different plant species, but recovery may vary depending on root type and water stress severity. Kr dynamics are proposed to modulate g_c response during and following drought.

Root hydraulic conductance shows a similar high sensitivity to soil water deficit in herbaceous and woody roots and may control canopy diffusive conductance during drought and following recovery.     

Role of coupled dynamics in the catalytic activity of prokaryotic-like prolyl-tRNA synthetases

Prolyl-tRNA synthetases (ProRSs) have been shown to activate both cognate and some noncognate amino acids and attach them to specific tRNA(Pro) substrates. For example, alanine, which is smaller than cognate proline, is misactivated by Escherichia coli ProRS. Mischarged Ala-tRNA(Pro) is hydrolyzed by an editing domain (INS) that is distinct from the activation domain. It was previously shown that deletion of the INS greatly reduced cognate proline activation efficiency. In this study, experimental and computational approaches were used to test the hypothesis that deletion of the INS alters the internal protein dynamics leading to reduced catalytic function. Kinetic studies with two ProRS variants, G217A and E218A, revealed decreased amino acid activation efficiency. Molecular dynamics studies showed motional coupling between the INS and protein segments containing the catalytically important proline-binding loop (PBL, residues 199-206). In particular, the complete deletion of INS, as well as mutation of G217 or E218 to alanine, exhibited significant effects on the motion of the PBL. The presence of coupled dynamics between neighboring protein segments was also observed through in silico mutations and essential dynamics analysis. Altogether, this study demonstrates that structural elements at the editing domain-activation domain interface participate in coupled motions that facilitate amino acid binding and catalysis by bacterial ProRSs, which may explain why truncated or defunct editing domains have been maintained in some systems, despite the lack of catalytic activity.     

l-Lactate metabolism in HEP G2 cell mitochondria due to the l-lactate dehydrogenase determines the occurrence of the lactate/pyruvate shuttle and the appearance of oxaloacetate, malate and citrate outside mitochondria

As part of an ongoing study of l-lactate metabolism both in normal and in cancer cells, we investigated whether and how l-lactate metabolism occurs in mitochondria of human hepatocellular carcinoma (Hep G2) cells. We found that Hep G2 cell mitochondria (Hep G2-M) possess an l-lactate dehydrogenase (ml-LDH) restricted to the inner mitochondrial compartments as shown by immunological analysis, confocal microscopy and by assaying ml-LDH activity in solubilized mitochondria. Cytosolic and mitochondrial l-LDHs were found to differ from one another in their saturation kinetics. Having shown that l-lactate itself can enter Hep G2 cells, we found that Hep G2-M swell in ammonium l-lactate, but not in ammonium pyruvate solutions, in a manner inhibited by mersalyl, this showing the occurrence of a carrier-mediated l-lactate transport in these mitochondria. Occurrence of the l-lactate/pyruvate shuttle and the appearance outside mitochondria of oxaloacetate, malate and citrate arising from l-lactate uptake and metabolism together with the low oxygen consumption and membrane potential generation are in favor of an anaplerotic role for l-LAC in Hep G2-M.     

Modification of macroporous titanium tracheal implants with biodegradable structures: tracking in vivo integration for determination of optimal in situ epithelialization conditions

Previously, we showed that macroporous titanium implants, colonized in vivo together with an epithelial graft, are viable options for tracheal replacement in sheep. To decrease the number of operating steps, biomaterial-based replacements for epithelial graft and intramuscular implantation were developed in the present study. Hybrid microporous PLLA/titanium tracheal implants were designed to decrease initial stenosis and provide a surface for epithelialization. They have been implanted in New Zealand white rabbits as tracheal substitutes and compared to intramuscular implantation samples. Moreover, a basement membrane like coating of the implant surface was also designed by Layer-by-Layer (LbL) method with collagen and alginate. The results showed that the commencement of stenosis can be prevented by the microporous PLLA. For determination of the optimum time point of epithelialization after implantation, HPLC analysis of blood samples, C-reactive protein (CRP), and Chromogranin A (CGA) analyses and histology were carried out. Following 3 weeks the implant would be ready for epithelialization with respect to the amount of tissue integration. Calcein-AM labeled epithelial cell seeding showed that after 3 weeks implant surfaces were suitable for their attachment. CRP readings were steady after an initial rise in the first week. Cross-linked collagen/alginate structures show nanofibrillarity and they form uniform films over the implant surfaces without damaging the microporosity of the PLLA body. Human respiratory epithelial cells proliferated and migrated on these surfaces which provided a better alternative to PLLA film surface. In conclusion, collagen/alginate LbL coated hybrid PLLA/titanium implants are viable options for tracheal replacement, together with in situ epithelialization.     

Surface properties of Helicobacter pylori urease complex are essential for persistence

The enzymatic activity of Helicobacter pylori's urease neutralises stomach acidity, thereby promoting infection by this pathogen. Urease protein has also been found to interact with host cells in vitro, although this property's possible functional importance has not been studied in vivo. To test for a role of the urease surface in the host/pathogen interaction, surface exposed loops that display high thermal mobility were targeted for inframe insertion mutagenesis. H. pylori expressing urease with insertions at four of eight sites tested retained urease activity, which in three cases was at least as stable as was wild-type urease at pH 3. Bacteria expressing one of these four mutant ureases, however, failed to colonise mice for even two weeks, and a second had reduced bacterial titres after longer term (3 to 6 months) colonisation. These results indicate that a discrete surface of the urease complex is important for H. pylori persistence during gastric colonisation. We propose that this surface interacts directly with host components important for the host-pathogen interaction, immune modulation or other actions that underlie H. pylori persistence in its special gastric mucosal niche.     

Constitutive Activity of the Human TRPML2 Channel Induces Cell Degeneration

The mucolipin (TRPML) ion channel proteins represent a distinct subfamily of channel proteins within the transient receptor potential (TRP) superfamily of cation channels. Mucolipin 1, 2, and 3 (TRPML1, -2, and -3, respectively) are channel proteins that share high sequence homology with each other and homology in the transmembrane domain with other TRPs. Mutations in the TRPML1 protein are implicated in mucolipidosis type IV, whereas mutations in TRPML3 are found in the varitint-waddler mouse. The properties of the wild type TRPML2 channel are not well known. Here we show functional expression of the wild type human TRPML2 channel (h-TRPML2). The channel is functional at the plasma membrane and characterized by a significant inward rectification similar to other constitutively active TRPML mutant isoforms. The h-TRPML2 channel displays nonselective cation permeability, which is Ca²⁺-permeable and inhibited by low extracytosolic pH but not Ca²⁺ regulated. In addition, constitutively active h-TRPML2 leads to cell death by causing Ca²⁺ overload. Furthermore, we demonstrate by functional mutation analysis that h-TRPML2 shares similar characteristics and structural similarities with other TRPML channels that regulate the channel in a similar manner. Hence, in addition to overall structure, all three TRPML channels also share common modes of regulation.