A role for actin arcs in the leading-edge advance of migrating cells

Epithelial cell migration requires coordination of two actin modules at the leading edge: one in the lamellipodium and one in the lamella. How the two modules connect mechanistically to regulate directed edge motion is not understood. Using live-cell imaging and photoactivation approaches, we demonstrate that the actin network of the lamellipodium evolves spatio-temporally into the lamella. This occurs during the retraction phase of edge motion, when myosin II redistributes to the lamellipodial actin and condenses it into an actin arc parallel to the edge. The new actin arc moves rearward, slowing down at focal adhesions in the lamella. We propose that net edge extension occurs by nascent focal adhesions advancing the site at which new actin arcs slow down and form the base of the next protrusion event. The actin arc thereby serves as a structural element underlying the temporal and spatial connection between the lamellipodium and the lamella during directed cell motion.     

Postglacial history of Atlantic oakwoods: Context,dynamics and controlling factors

Summary

We present here a review of the recolonisation of the Atlantic oakwoods following the end of the last glacial period. The study is based on two independent data sources: palaeoecological and phylogeographical data. The spread of oak is examined at two scales: (1) continental, allowing a consideration of the location of glacial refugia and the broad outlines of the migration, (2) the Atlantic coastal region, in order to establish the specific history of the Atlantic oakwoods. Climatic and human controls on the timing, speed and pattern of spread are considered, in particular, the conditions of the early Holocene period during which the majority of the recolonisation took place.     

Conserved Amphipathic Helices Mediate Lipid Droplet Targeting of Perilipins 1–3

Perilipins (PLINs) play a key role in energy storage by orchestrating the activity of lipases on the surface of lipid droplets. Failure of this activity results in severe metabolic disease in humans. Unlike all other lipid droplet-associated proteins, PLINs localize almost exclusively to the phospholipid monolayer surrounding the droplet. To understand how they sense and associate with the unique topology of the droplet surface, we studied the localization of human PLINs in Saccharomyces cerevisiae, demonstrating that the targeting mechanism is highly conserved and that 11-mer repeat regions are sufficient for droplet targeting. Mutations designed to disrupt folding of this region into amphipathic helices (AHs) significantly decreased lipid droplet targeting in vivo and in vitro. Finally, we demonstrated a substantial increase in the helicity of this region in the presence of detergent micelles, which was prevented by an AH-disrupting missense mutation. We conclude that highly conserved 11-mer repeat regions of PLINs target lipid droplets by folding into AHs on the droplet surface, thus enabling PLINs to regulate the interface between the hydrophobic lipid core and its surrounding hydrophilic environment.     

Characterization of a human coagulation factor Xa-binding site on <Emphasis Type="Italic">Viperidae</Emphasis> snake venom phospholipases A<Subscript>2</Subscript> by affinity binding studies and molecular bioinformatics

Background  

The snake venom group IIA secreted phospholipases A₂ (SVPLA₂), present in the Viperidae snake family exhibit a wide range of toxic and pharmacological effects. They exert their different functions by catalyzing the hydrolysis of phospholipids (PL) at the membrane/water interface and by highly specific direct binding to: (i) presynaptic membrane-bound or intracellular receptors; (ii) natural PLA₂-inhibitors from snake serum; and (iii) coagulation factors present in human blood.     

Renin-angiotensin system polymorphisms in relation to hypertension status and obesity in a Tunisian population

Essential hypertension (HTA) is the clinical expression of a disordered interaction between the genetic, physiological, and biochemical systems that under usual conditions maintain cardiovascular homeostasis. We studied the effects of the angiotensinogen M235T, angiotensin converting enzyme insertion/deletion (ACE I/D), and angiotensin II receptor 1 (AT1R) A1166C gene polymorphisms on the risk of HTA and to evaluate the relationship between these polymorphisms and obesity. We performed AGT, ACE and AGTR genotyping in 142 hypertensive patients and 191 control subjects using PCR-RFLP methods and PCR, respectively. The three polymorphisms were significantly associated with HTA. Individuals carrying the mutated TT of AGT, DD of ACE and CC of AT1R genotypes had an 1.67 (P = 0.032), 3.09 (P < 0.001) and 3.45 (P < 0.001)-fold increased risk of HTA. After adjustment for sex, smoking, diabetes, dyslipidemia, BMI, triglycerides and DD, TT and CC genotypes, BMI was independent risk factor of HTA (OR = 3.14; P < 0.001). An association of BMI with ACE gene polymorphism (P = 0.035), whereas no association with AGT and AT1R gene polymorphisms was obtained. The proportion of hypertensives is as high as 21.8 and 13.4% in the overweight and the obese DD group. The present study implies that the genotyping for the variants of RAS gene could in the future become an important part of the clinical process of risk identification for HTA.     

Variation in volatile leaf oils of seven eucalyptus species harvested from Zerniza arboreta (Tunisia)

Leaves of seven species of the genus Eucalyptus L'Hér., viz., E. cladocalyx F. Muell., E. citriodora Hook., E. diversicolor F. Muell., E. fasciculosa F. Muell., E. grandis W. Hill, E. ovata Labill., and E. botryoides Sm., were harvested from Zerniza arboreta (region of Sejnene, northwest of Tunisia) in June 2007. Of the latter species, leaves were collected from trees having two origins, Morocco and Italy. Hydrodistillation of the dried leaves provided essential oils in yields varying from 0.4±0.0 to 3.3±0.1%, according to the species. E. citriodora had the highest mean percentage of essential oil amongst the species examined, whereas the lowest one was obtained for E. botryoides originating from Morocco. Analysis by GC (RI) and GC/MS allowed the identification of 140 compounds, representing 92.5 to 99.4% of the total oil composition. The contents of the different samples varied according to the species. The main components were 1,8-cineole (2), followed by α-pinene (1), p-cymene, borneol, α-terpineol, cryptone, spathulenol, trans-pinocarveol (4), bicyclogermacrene (5), caryophyllene oxide, and β-phellandrene. Principal components analysis and hierarchical cluster analysis separated the eight Eucalyptus leaf essential oils into five groups, each constituting a chemotype.