The Bmp gradient of the zebrafish gastrula guides migrating lateral cells by regulating cell-cell adhesion

BACKGROUND: Bone morphogenetic proteins (Bmps) are required for the specification of ventrolateral cell fates during embryonic dorsoventral patterning and for proper convergence and extension gastrulation movements, but the mechanisms underlying the latter role remained elusive. RESULTS: Via bead implantations, we show that the Bmp gradient determines the direction of lateral mesodermal cell migration during dorsal convergence in the zebrafish gastrula. This effect is independent of its role during dorsoventral patterning and of noncanonical Wnt signaling. However, it requires Bmp signal transduction through Alk8 and Smad5 to negatively regulate Ca(2+)/Cadherin-dependent cell-cell adhesiveness. In vivo, converging mesodermal cells form lamellipodia that attach to adjacent cells. Bmp signaling diminishes the Cadherin-dependent stability of such contact points, thereby abrogating subsequent cell displacement during lamellipodial retraction. CONCLUSIONS: We propose that the ventral-to-dorsal Bmp gradient has an instructive role to establish a reverse gradient of cell-cell adhesiveness, thereby defining different migratory zones and directing lamellipodia-driven cell migrations during dorsal convergence in lateral regions of the zebrafish gastrula.     

Incorporation of PEG-lipids in arsonoliposomes results in formation of highly stable arsenic-containing vesicles

We investigated the effect of pegylation on the physical stability, morphology and membrane integrity of arsonoliposomes. Arsonoliposomes composed of distearoylglycerophosphocholine (DSPC), cholesterol (Chol) and the palmitoyl side chain arsonolipid (with concentrations ranging from 0 mol% [DSPC/Chol vesicles] to 53 mol% of total lipid) containing either 4 or 8 mol% DPPE-PEG2000 or DSPE-PEG2000, were prepared by sonication. Arsonoliposome membrane integrity was evaluated by measuring the retention of encapsulated calcein in vesicles (during incubation in buffer or fetal calf serum [FCS]) while physical stability was evaluated by measuring vesicle dispersion turbidity (during incubation in water or CaCl(2)). Vesicle morphology was studied by cryo-electron microscopy. Experimental results show that: (i) PEG-lipids are incorporated in arsonoliposomes (as confirmed by the vesicle zeta potential modulation), (ii) pegylation of arsonoliposomes prevents their aggregation and fusion in the presence of calcium ions and (iii) when 8 mol% of PEG-DSPE is incorporated in arsonoliposomes based on their arsonolipid content, two groups of pegylated vesicles are formed: low content arsonoliposomes (<20 mol% arsonolipid) which are highly leaky and high content arsonoliposomes (>27 mol% arsonolipid) which are highly stable (70% calcein retention after 24h incubation in fetal calf serum [FCS]). In addition to high membrane integrity, the high content pegylated arsonoliposomes are morphologically perfect round-shaped vesicles without the sharp edges typically observed with non-pegylated DSPC-containing arsonoliposomes.     

Enhancement of physical weathering of building stones by microbial populations

Two limestones from Crete, Greece and a dolomite from Mansfield, UK were subjected to combined microbial and physical weathering simulation cycles, in an attempt to assess the contribution of each agent of decay. Sound stone discs were exposed to different temperature and wet/dry cycling regimes involving treatment with distilled water or solutions of sodium chloride or sodium sulphate. Before the weathering cycles, half of the discs were inoculated with mixed microbial populations (MMP), originally recovered from decayed building stone of Portchester Castle, Hampshire, UK. The presence of MMP greatly accelerated the rates of deterioration of stone of all treatments, measured by weight change and alteration of hydraulic properties of stone. A combination of physical and biological processes significantly enhanced the extent of decay when compared with the physical or biological agents acting alone. Populations of heterotrophic, sulphur-utilising, halotolerant and moderately halophilic bacterial populations remained large throughout the experiment. Biofilms formed by populations of microorganisms were visualised by staining and assessed by colorimetric measurement of total carbohydrate in the stone substrate. The relative contribution of microbial and physical weathering to the process is discussed.     

Effect of 17β-estradiol on adhesion of Mytilus galloprovincialis hemocytes to selected substrates. Role of alpha2 integrin subunit

The process of hemocyte adhesion to extracellular matrix (ECM) proteins plays a crucial role in cell immunity. In most of these interactions between ECM proteins and cells, integrins are involved. The results of the present study showed that incubation of Mytilus galloprovincialis hemocytes with 17β-estradiol caused significant increased adhesion of hemocytes to ECM proteins and specifically to laminin-1, collagen IV and oxidized collagen IV, in relation to control cells. The adhesion of hemocytes to oxidized collagen was significantly higher than to either collagen IV or to laminin-1. In accordance with this, inhibition of either NADPH oxidase or nitric oxide (NO) synthase attenuated 17β-estradiol effect on hemocyte adhesion, suggesting that the high levels of free radicals, produced after 17β-estradiol effect, could contribute to the high adhesion of hemocytes to laminin-1 and collagen IV. The implication of ROS was further confirmed by the use of the oxidant rotenone, which caused elevation of cell adhesion in relation to control and by the antioxidant NAC which attenuated 17β-estradiol effect. The mechanism of 17β-estradiol induced adhesion to laminin-1, collagen IV and oxidized collagen IV involves a large number of intracellular components, as Na+/H+ exchanger (NHE), all isoforms of protein kinase C (PKC), phosphatidylinositol-3-kinase (PI3K) and c-jun N-terminal kinase (JNK) as well as alpha2 integrin subunit. Maintenance of high cyclic adenosine-3'-5'-monophosphate (cAMP) levels caused non significant higher adhesion of hemocytes to ECM proteins in relation to control cells. Our results showed that 17β-estradiol caused a significant increase in α? integrin subunit levels, which was reduced after inhibition of NHE, PI3K, PKC, NO synthase, NADPH oxidase and JNK. In addition, our results showed that apart from 17β-estradiol, high cAMP and high ROS levels caused significantly higher induction of α? integrin subunit levels in relation to control. Our results imply a potential involvement of cAMP in immune responses of Mytilus hemocytes, which needs further investigation.     

Effects of ATP and NGF on Proliferation and Migration of Neural Precursor Cells

Neurochemical Research - Purinergic receptors belong to the most ancient neurotransmitter system. While their relevance in neurotransmission is well characterized, it has become clear that they...     

Impact of Regional Vein Thrombosis in Patients with Klebsiella pneumoniae Liver Abscess

Klebsiella liver abscess (KLA) is an emerging infection in Asia caused by hypermucoviscous strains of Klebsiella pneumoniae. It is associated with thrombophlebitis of portal and hepatic veins. The natural history and role of anticoagulation for this regional thrombophlebitis is unclear. In a retrospective study of 169 subjects with KLA over 7 years, thrombophlebitis was identified in 53/169 (31.4%). Only 1 received therapeutic anticoagulation. Despite this 30/49 (73.2%) of those with follow up scan available showed improvement or recanalization (mean duration between scans 44 days). Abscess resolution was associated with improvement in thrombophlebitis.     

Deoxyuridine triphosphatase expression defines the transition from dormant to sprouting potato tuber buds

Identification of molecular markers defining the end of tuber dormancy prior to visible sprouting is of agronomic interest for potato growers and the potato processing industry. In potato tubers, breakage of dormancy is associated with the reactivation of meristem function. In dormant meristems, cells are arrested in the G₁/G₀ phase of the cell cycle and re-entry into the G₁ phase followed by DNA replication during the S phase enables bud outgrowth. Deoxyuridine triphosphatase (dUTPase) is essential for DNA replication and was therefore tested as a potential marker for meristem reactivation in tuber buds. The corresponding cDNA clone was isolated from potato by PCR. The deduced amino acid sequence showed 94% similarity to the tomato homologue. By employing different potato cultivars, a positive correlation between dUTPase expression and onset of tuber sprouting could be confirmed. Moreover, gene expression analysis of tuber buds during storage time revealed an up-regulation of the dUTPase 1 week before visible sprouting occurred. Further analysis using an in vitro sprout assay supported the assumption that dUTPase is a good molecular marker to define the transition from dormant to active potato tuber meristems.     

Even Weak Males Help Their Neighbours: Defence Coalitions in a Fiddler Crab

Large male fiddler crabs sometimes help smaller neighbours to defend their territories against intruders. These coalitions occur when the helper is likely to defeat the intruder (helper larger than intruder) and the neighbour is likely to lose his territory without help (intruder larger than neighbour). Previous studies of coalitions have excluded males with regenerated claws. Such claws are weaker weapons that make the bearer competitively inferior. Here, we show that male Uca annulipes with regenerated claws are as likely as males with original claws to help their neighbours in territory defence, even though, as weaker males they potentially pay greater costs, being more likely to lose their undefended burrow. We suggest that males with regenerated claws gain greater benefits from retaining a current, small neighbour and that, as in non‐coalition fights, the regenerated claw acts as a visual bluff in the early stages of combat. Furthermore, we show that intruders with regenerated or original claws are equally likely to be attacked by a ‘helping’ neighbour. This bolsters the argument that males cannot visually differentiate between original and regenerated claws.     

Insights into FlaI Functions in Archaeal Motor Assembly and Motility from Structures,Conformations, and Genetics

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Highlights? Cross-subunit interface forms building block for transmission of ATPase force ? Structures and mutants reveal functional components for assembly and motility ? The directionality of movement explains FlaI activities and GspE differences ? The phosphate released by ATP hydrolysis triggers subunit rearrangements     

Ceramide triggers intracellular calcium release via the IP3 receptor in Xenopus laevis oocytes

Ceramide, a product of sphingomyelin turnover, is a lipid secondmessenger that mediates diverse signaling pathways, including thoseleading to cell cycle arrest and differentiation. The mechanism(s) bywhich ceramide signals downstream events have not been fully elucidated. Here we show that, in Xenopuslaevis oocytes, ceramide-induced maturation isassociated with the release of intracellular calcium stores. Ceramidecaused a dose-dependent elevation in the second messenger inositol1,4,5-trisphosphate (IP₃) viaactivation of G_q/11 andphospholipase C-X. Elevation ofIP₃, in turn, activated theIP₃ receptor calcium releasechannel on the endoplasmic reticulum, resulting in a rise incytoplasmic calcium. Thus our study demonstrates that cross talkbetween the ceramide and phosphoinositide signaling pathways modulatesintracellular calcium homeostasis.