Differences in the electrostatic surfaces of the type III secretion needle proteins PrgI, BsaL, and MxiH

Gram-negative bacteria use a needle-like protein assembly, the type III secretion apparatus, to inject virulence factors into target cells to initiate human disease. The needle is formed by the polymerization of approximately 120 copies of a small acidic protein that is conserved among diverse pathogens. We previously reported the structure of the BsaL needle monomer from Burkholderia pseudomallei by nuclear magnetic resonance (NMR) spectroscopy and others have determined the crystal structure of the Shigella flexneri MxiH needle. Here, we report the NMR structure of the PrgI needle protein of Salmonella typhimurium, a human pathogen associated with food poisoning. PrgI, BsaL, and MxiH form similar two helix bundles, however, the electrostatic surfaces of PrgI differ radically from those of BsaL or MxiH. In BsaL and MxiH, a large negative area is on a face formed by the helix alpha1-alpha2 interface. In PrgI, the major negatively charged surface is not on the "face" but instead is on the "side" of the two-helix bundle, and only residues from helix alpha1 contribute to this negative region. Despite being highly acidic proteins, these molecules contain large basic regions, suggesting that electrostatic contacts are important in needle assembly. Our results also suggest that needle-packing interactions may be different among these bacteria and provide the structural basis for why PrgI and MxiH, despite 63% sequence identity, are not interchangeable in S. typhimurium and S. flexneri.     

Megf10 regulates the progression of the satellite cell myogenic program

We identify here the multiple epidermal growth factor repeat transmembrane protein Megf10 as a quiescent satellite cell marker that is also expressed in skeletal myoblasts but not in differentiated myofibers. Retroviral expression of Megf10 in myoblasts results in enhanced proliferation and inhibited differentiation. Infected myoblasts that fail to differentiate undergo cell cycle arrest and can reenter the cell cycle upon serum restimulation. Moreover, experimental modulations of Megf10 alter the expression levels of Pax7 and the myogenic regulatory factors. In contrast, Megf10 silencing in activated satellite cells on individual fibers or in cultured myoblasts results in a dramatic reduction in the cell number, caused by myogenin activation and precocious differentiation as well as a depletion of the self-renewing Pax7⁺/MyoD⁻ population. Additionally, Megf10 silencing in MyoD^−/− myoblasts results in down-regulation of Notch signaling components. We conclude that Megf10 represents a novel transmembrane protein that impinges on Notch signaling to regulate the satellite cell population balance between proliferation and differentiation.     

Genetic and molecular regulation of fruit and plant domestication traits in tomato and pepper

Tomato and pepper are two Solanaceous fruit crops that display an enormous diversity in fruit morphology. In this review, we will present an overview of the history of tomato and pepper and discuss key plant traits that were specifically selected during domestication of the two species. The traits discussed are fruit weight, shape, colour, ripening, pungency and plant architecture. We will review these characteristics as well as the genetic loci or genes that control these features, questioning whether mutations at orthologous loci occurred independently in these two species or whether unique plant and fruit features resulted in selection at different genes.     

S-allylcysteine mediates cardioprotection in an acute myocardial infarction rat model via a hydrogen sulfide-mediated pathway

S-allylcysteine (SAC) is an organosulfur-containing compound derived from garlic. Studies have shown that garlic is beneficial in the treatment of cardiovascular diseases. This study aims to elucidate if SAC is responsible for this cardioprotection using acute myocardial infarction (AMI) rat models. In addition, we hypothesized that SAC may mediate cardioprotection via a hydrogen sulfide (H(2)S)-related pathway. Rats were pretreated with saline, SAC (50 mg x kg(-1) x day(-1)), SAC + propagylglycine (PAG; 50 mg + 10 mg x kg(-1) x day(-1)) or PAG (10 mg x kg(-1) x day(-1)) for 7 days before AMI induction and killed 48 h after. Our results showed that SAC significantly lowered mortality (12.5% vs. 33.3%, P < 0.05) and reduced infarct size. SAC + PAG- and PAG-treated rats had larger infarct sizes than controls (60.9 +/- 0.01 and 62.0 +/- 0.03%, respectively, vs. 50.0 +/- 0.03%; P < 0.05). Pretreatment with SAC did not affect BP, but BP was significantly elevated in SAC + PAG and PAG-treated groups (P < 0.05). In addition, plasma H(2)S levels and left ventricular cystathionine-gamma-lyase (CSE) activities were analyzed to investigate the involvement of H(2)S. CSE is the enzyme responsible for H(2)S production in the heart. SAC increased left ventricular CSE activity in AMI rats (2.75 +/- 0.34 vs. 1.23 +/- 0.16 micromol x g protein(-1) x h(-1); P < 0.01). SAC + PAG-treated rats had significantly lower CSE activity compared with the SAC-treated group (1.22 +/- 0.27 vs. 2.75 +/- 0.34 micromol x g protein(-1) x h(-1); P < 0.05). Similarly, SAC-treated rats had higher plasma H(2)S concentration compared with controls and the SAC + PAG-treated group. Protein expression studies revealed that SAC upregulated CSE expression (1.1-fold of control; P < 0.05), whereas SAC + PAG and PAG downregulated its expression (0.88-fold of control in both groups; P < 0.005). In conclusion, our study provides novel evidence that SAC is protective in myocardial infarction via an H(2)S-related pathway.     

The salvador-warts-hippo pathway is required for epithelial proliferation and axis specification in Drosophila

In Drosophila, the body axes are specified during oogenesis through interactions between the germline and the overlying somatic follicle cells [1-5]. A Gurken/TGF-alpha signal from the oocyte to the adjacent follicle cells assigns them a posterior identity [6, 7]. These posterior cells then signal back to the oocyte, thereby inducing the repolarization of the microtubule cytoskeleton, the migration of the oocyte nucleus, and the localization of the axis specifying mRNAs [8-10]. However, little is known about the signaling pathways within or from the follicle cells responsible for these patterning events. We show that the Salvador Warts Hippo (SWH) tumor-suppressor pathway is required in the follicle cells in order to induce their Gurken- and Notch-dependent differentiation and to limit their proliferation. The SWH pathway is also required in the follicle cells to induce axis specification in the oocyte, by inducing the migration of the oocyte nucleus, the reorganization of the cytoskeleton, and the localization of the mRNAs that specify the anterior-posterior and dorsal-ventral axes of the embryo. This work highlights a novel connection between cell proliferation, cell growth, and axis specification in egg chambers.     

Stochastic emergence of repeating cortical motifs in spontaneous membrane potential fluctuations in vivo

It was recently discovered that subthreshold membrane potential fluctuations of cortical neurons can precisely repeat during spontaneous activity, seconds to minutes apart, both in brain slices and in anesthetized animals. These repeats, also called cortical motifs, were suggested to reflect a replay of sequential neuronal firing patterns. We searched for motifs in spontaneous activity, recorded from the rat barrel cortex and from the cat striate cortex of anesthetized animals, and found numerous repeating patterns of high similarity and repetition rates. To test their significance, various statistics were compared between physiological data and three different types of stochastic surrogate data that preserve dynamical characteristics of the recorded data. We found no evidence for the existence of deterministically generated cortical motifs. Rather, the stochastic properties of cortical motifs suggest that they appear by chance, as a result of the constraints imposed by the coarse dynamics of subthreshold ongoing activity.     

Differential Gene Expression in a Marine Sponge in Relation to Its Symbiotic State

The molecular mechanisms involved in the establishment and maintenance of sponge photosymbiosis, and in particular the association with cyanobacteria, are unknown. In the present study we analyzed gene expression in a common Mediterranean sponge (Petrosia ficiformis) in relation to its symbiotic (with cyanobacteria) or aposymbiotic status. A screening approach was applied to identify genes expressed differentially in symbiotic specimens growing in the light and aposymbiotic specimens growing in a dark cave at a short distance from the illuminated specimens. Out of the various differentially expressed sequences, we isolated two novel genes (here named PfSym1 and PfSym2) that were up-regulated when cyanobacterial symbionts were harbored inside the sponge cells. The sequence of one of these genes (PfSym2) was found to contain a conserved domain: the scavenger receptor cysteine rich (SRCR) domain. This is the first report on the expression of sponge genes in relation to symbiosis and, according to the presence of an SRCR domain, we suggest possible functions for one of the genes found in the sponge-cyanobacteria symbiosis.