A synaptojanin-homologous region of Salmonella typhimurium SigD is essential for inositol phosphatase activity and Akt activation

The Ser-Thr kinase Akt is activated in epithelial cells by Salmonella enterica serovar typhimurium. The bacterial effector SigD, which is translocated into host cells via the specialized type III secretion system, is essential for Akt activation. Here, we investigated the inositol phospholipid substrate preferences of SigD. Recombinant SigD preferentially dephosphorylated phosphatidylinositol 3,5-biphosphate and phosphatidylinositol 3,4,5-triphosphate over other phosphatidylinositol lipids. Phosphatidylinositol 3-phosphate was not a substrate, suggesting the 5' phosphate moiety is one of the preferred substrates. Database searches revealed that SigD bears a small region of homology to the mammalian type II inositol 5-phosphatase synaptojanin. Mutation of two conserved residues in this region, Lys527 and Lys530, decreased or abrogated phosphatase activity, respectively. The Shigella flexneri SigD homologue, IpgD, displayed a similar activity in vitro and also activated Akt when used to complement a DeltasigD Salmonella strain. A mutation in IpgD at Lys507, analogous to Lys530 of SigD, also failed to activate Akt. Thus, we have characterized a region near the carboxyl-terminus of SigD which is important for phosphatase activity. We discuss how dephosphorylation of inositol phospholipids by SigD in vivo might contribute to the activation of Akt.     

PIP kinase Igamma is the major PI(4,5)P(2) synthesizing enzyme at the synapse

Disruption of the presynaptically enriched polyphosphoinositide phosphatase synaptojanin 1 leads to an increase of clathrin-coated intermediates and of polymerized actin at endocytic zones of nerve terminals. These changes correlate with elevated levels of PI(4,5)P(2) in neurons. We report that phosphatidylinositol phosphate kinase type Igamma (PIPKIgamma), a major brain PI(4)P 5-kinase, is concentrated at synapses. Synaptojanin 1 and PIPKIgamma antagonize each other in the recruitment of clathrin coats to lipid membranes. Like synaptojanin 1 and other proteins involved in endocytosis, PIPKIgamma undergoes stimulation-dependent dephosphorylation. These results implicate PIPKIgamma in the synthesis of a PI(4,5)P(2) pool that acts as a positive regulator of clathrin coat recruitment and actin function at the synapse.     

Short-term dynamics of an acacia ant community in Laikipia,Kenya

In monospecific stands of Acacia drepanolobium in Laikipia, Kenya, virtually all but the smallest trees are occupied by one of four species of ants. Although trees are a limiting resource, all four ant species are maintained in this system. Three separate lines of evidence confirm a linear dominance hierarchy among these four ants: (1) experimentally staged conflicts, (2) natural transitions among 1773 tagged trees over a 6-month period, and (3) the average sizes of trees occupied by ants of different species. Short-term dynamics during a drying period reveal that many smaller trees (<1 m) occupied by dominant ants were subsequently abandoned, and that abandoned trees had grown more slowly than those that were not abandoned. Height growth increments over 6 months were generally independent of ant occupant, but increased with tree height. Among taller trees (>1 m), changes in ant occupation congruent with the dominance hierarchy (i.e., transitions from more subordinate ant species to more dominant ant species) occurred on trees that grew faster than average. In contrast, the (less frequent) changes in ant occupation ”against” the direction of the dominance hierarchy occurred on trees that grew more slowly than average. Observed correlations between tree vigor and takeover direction suggest that colony growth of dominant ant species is either favored in more productive microhabitats, or that such colonies differentially seek out healthier trees for conquest. Colonies of dominant species may differentially abandon more slowly growing trees during (dry) periods of retrenchment, or suffer higher mortality on these trees. Subordinate ant species appear to move onto these abandoned trees and, to a lesser extent, colonize new recruits in the sapling class. These data reveal that within a simple linear dominance hierarchy, short-term variations exist that may reveal underlying mechanisms associated with coexistence. Received: 24 June 1999 / Accepted: 3 December 1999     

HMGA2 expression in white adipose tissue linking cellular senescence with diabetes

There is a clear link between overweight, gain of white adipose tissue, and diabetes type 2 (T2D). The molecular mechanism of the gain of adipose tissue is linked with the expression of high mobility group protein AT-hook 2 (HMGA2), and recent studies revealed an association with a SNP near HMGA2. In this study, we investigated the gene expression of HMGA2, p14^Arf, CDKN1A, and BAX in human abdominal subcutaneous white adipose tissue from 157 patients. We found a significant higher HMGA2 expression in obese individuals than in non-obese patients. Furthermore, the HMGA2 expression in white adipose tissue in patient with type 2 diabetes was significantly higher than in nondiabetic patients. There is an association between the DNA-binding nonhistone protein HMGA2 and the risk of developing T2D that remains mechanistically unexplained so far. Likewise, p14^Arf, an inducer of cellular senescence, has been associated with the occurrence of T2D. The data of the present study provide evidence that both proteins act within the same network to drive proliferation of adipose tissue stem and precursor cells, senescence, and increased risk of T2D, respectively.

Electronic supplementary material

The online version of this article (doi:10.1007/s12263-013-0354-6) contains supplementary material, which is available to authorized users.     

Polar lipid derangements in type 2 diabetes mellitus: potential pathological relevance of fatty acyl heterogeneity in sphingolipids

While pathological alterations in plasma neutral lipids with type 2 diabetes mellitus (T2DM) has been relatively well-characterized, only limited information is available on the variations in global polar lipidome (glycerophospholipids and sphingolipids) with the disease. To systematically identify polar lipid aberrations associated with early stage T2DM, we quantitatively profiled and compared changes in more than 300 plasma lipid species from distinct groups of T2DM patients against overtly healthy controls. Sphingolipid classes including ceramides, sphingomyelins, lactosylceramides (LacCer) and ganglioside GM3 (GM3) were significantly elevated in mild T2DM with a concomitant decrease in glucosylceramides (GluCer), suggesting the increased conversion of GluCer to LacCer in mild diabetes. Individual GM3 species were altered in T2DM according to their acyl chain lengths. While long-chain GM3s (fatty acyl carbon ≥18) were significantly increased in T2DM, the opposite was observed for GM3 18:1/16:0. Importantly, long-chain GM3 species were negatively correlated with HOMA2-%β and positively correlated with FBG; and could distinguish between healthy individuals and mildly diabetic patients with similar HOMA2-%β. The current study therefore identifies metabolic alterations in sphingolipid pathways as early events in T2DM pathogenesis, and provides hypothesis-generating new insights relevant for larger scale clinical studies aimed at identification of early molecular markers of T2DM.     

Morphological differences among egg nests and adult individuals of Cicadatra persica (Hemiptera,Cicadidae), distributed in Erneh,Syria

The aim of this study is determining the different patterns of egg nests and the morphological differences between the specimens of Cicadatra persica Kirkalidy, 1909 (Hemiptera: Cicadidae) distributed in fruit orchards in Erneh located on AL-Sheikh mountain south west of Syria. The appearance of 80 egg nests was studied, and the results showed that there were two basic patterns of egg nests laid by Cicadatra persica, 90% of the egg nests were of the first pattern (consists of several adjacent slits), while 10% of them were of the second pattern (consists of several divergent slits). A random sample consisting of 300 specimens (150 males and 150 females) were also studied concentrating on the differences in the color of the supra-antennal plate and in the number of spurs on the tibia of the hind legs. The results showed that there were two basic patterns of individuals based on the differences in the color of supra-antennal plate. The first pattern (individuals with yellow supra-antennal plates), constituted more than 90%, and the second one (individuals with black supra-antennal plates) constituted less than 10%. The results also showed that there were 27 different patterns based on the number of spurs on the tibia of the hind legs. One of them was a common pattern (2, 3) whose individuals have 2 spurs on the upper side of the tibia of the hind legs and 3 spurs on the lateral side of the tibia of the hind legs. The total percent of this common pattern was 76%. The other 26 patterns were different from each other, and the total percent of all these different patterns was 24%.     

Sialic Acid Linkage in Glycosphingolipids Is a Molecular Correlate for Trafficking and Delivery of Extracellular Cargo

Gangliosides, glycosphingolipids containing sialic acid moieties, are well known mediators of transmembrane signaling and endocytosis at the plasma membrane. However, little is known about their precise regulatory role at the cell periphery for intracellular sorting of extracellular cargo. Here we inspected published scientific literature for two types of cargoes, namely bacterial toxins and viruses, regarding their usage of gangliosides. We derived a rather simple yet surprisingly consistent framework to classify 20 viruses from 12 different families and five type AB bacterial toxins into two broad categories. We propose that gangliosides with terminally attached sialic acids classify cargo for uptake and trafficking early in the endocytic pathway while gangliosides with internally attached sialic acids associate with uptake and trafficking of cargo late in the endocytic system. Our study provides a testable hypothesis for future investigations into a wide range of trafficking events. It could be utilized as a framework for other intracellular pathogens where lipids are known to be involved in recognition and trafficking. For instance, predictions can be put forward and evaluated based on ganglioside binding patterns and intracellular trafficking routes. Finally, incorporation of our classifier into large scale systems‐biology studies could help reveal related molecular determinants in subcellular sorting .     

Collagenase predigestion on paraffin sections enhances collagen immunohistochemical detection without distorting tissue morphology

Reliable immunohistochemical detection of collagen in formalin fixed, paraffin embedded tissues requires protease digestion. While these pan-proteases (pepsin, trypsin, protease K, etc.) enhance collagen detection, they also digest many other tissue proteins and produce poor cellular morphology and unrecognizable cellular structures. Balancing the conditions (protease type, concentration, incubation time and temperature) to digest some, but not all, proteins in a tissue section while optimizing collagen detection requires one to compromise improved collagen immunolabeling with adequate cellular morphology. Furthermore, optimal conditions for digesting tissue proteins to enhance collagen detection vary among tissue types and their fixation. Although brain is not typically subject to these deleterious consequences, structures such as epithelium, spermatids, stroma etc. and other tissues with complicated histology are profoundly affected. To resolve this technical dilemma, we discovered a novel use for collagenase to enhance collagen immunodetection without affecting the noncollagen proteins, thereby preserving tissue morphology. Collagenase, which is typically used in vitro for disassociation of cells, has never been used reliably on formalin fixed, paraffin embedded tissue sections. This new use of collagenase for immunohistochemistry promotes increased collagen immunolabeling, is easy to use, is versatile, and allows preservation of tissue structure that provides maximal and accurate histological information.