Transport of outer membrane lipids in mycobacteria

The complex organization of the mycobacterial cell wall poses unique challenges for the study of its assembly. Although mycobacteria are classified evolutionarily as Gram-positive bacteria, their cell wall architecture more closely resembles that of Gram-negative organisms. They possess not only an inner cytoplasmic membrane, but also a bilayer outer membrane that encloses an aqueous periplasm and includes diverse lipids that are required for the survival and virulence of pathogenic species. Questions surrounding how mycobacterial outer membrane lipids are transported from where they are made in the cytoplasm to where they function at the cell exterior are thus similar, and similarly compelling, to those that have driven the study of Gram-negative outer membrane transport pathways. However, little is understood about these processes in mycobacteria. Here we contextualize these questions by comparing our current knowledge of mycobacteria with better-defined systems in other organisms. Based on this analysis, we propose possible models and highlight continuing challenges to improving our understanding of outer membrane assembly in these medically and environmentally important bacteria. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.     

Transport of molecules and organelles in meroistic ovarioles of insects

Abstract. Transport of macromolecules from the nurse cells to the oocyte has been well documented in meroistic ovarioles of insects. The transport mechanism, however, has remained elusive. Cytoskeletal elements presumably play a role in the transport process in some species, but comparative studies have revealed dramatic differences in the structural organization of microfilaments and microtubules, indicating that these elements may serve different functions. Based on electrophysiological data, it has been suggested that charged molecules move by intercellular electrophoresis. However, recent evidence suggests that this mechanism cannot account for the transport phenomena observed in Drosophila and in some other species. It is proposed that as an alternative (or additional) transport mechanism, an osmotically driven pressure flow from the nurse cells to the oocyte might operate in the ovarioles of some insects.     

Cuticular lipids of insects. VI. Cuticular lipids of the grasshoppers Melanoplus sanguinipes and Melanoplus packardii

The cuticular lipids of the grasshoppers Melanoplus sanguinipes and Melanoplus packardii contain 60 and 68% alkanes and 28 and 18% secondary alcohol wax esters, respectively, with lesser amounts of normal and sterol wax esters, triglycerides, alcohols, sterols, and free fatty acids. All the hydrocarbons are saturated, and four types of alkanes are present: n-alkanes, 3-methylalkanes, internally branched monomethylalkanes, and internally branched dimethylalkanes. The principal n-alkanes in both insects are C(29) and C(27), with a range from C(21) to C(33). Trace amounts of 3-methylalkanes of 28, 30, and 32 total carbons are present. The principal internally branched monomethylalkanes are C(32) and C(34), whereas the main dimethylalkane contains 35 carbons. The n-alkanes do not correspond in chain length to the secondary alcohols. The primary alcohols range from C(22) to C(32) in both insects, with C(24) and C(26) predominating. The fatty acids in the triglyceride and free fatty acid fractions range from C(12) to C(24) in M. sanguinipes and from C(12) to C(18) in M. packardii.     

The role of lipids as feeding stimulants for shredding aquatic insects

SUMMARY.

• 1 Caddisflies (Trichoptera) that shred leaf detritus preferentially ingested lipid-coated detritus during the last larval in star. This is the interval when these insects accumulate the triglyceride reserves necessary for metamorphosis and reproduction. Early in star larvae, which do not accumulate lipids, showed no preference for any lipids. This behaviour indicates food selection based on changing nutritional needs.
• 2 Pure unsaturated 18- and 20-carbon fatty acids, either as free acids or triglycerides, were most strongly preferred. Crude lipid and the neutral lipid fraction from aquatic hyphomycete fungi, an important component of aquatic leaf detritus, were also preferred.
• 3 Tipula abdominalis (Diptera: Tipulidae) did not prefer any lipids during the last instar.

     

Plant and insect cuticular lipids serve as behavioral cues for insects

The roles of plant and insect cuticular lipids in insect and plant interactions are reviewed. Emphasis is given to the influence that the host plant and the surface lipids of the host plant have upon insect herbivores and the predators and parasitoids of these herbivores. Variations in cuticular lipids of herbivorous insects are dependent upon the host plant, and these variations may affect the behavior of predators and parasitoids. The cuticular lipids of species which interact on multiple trophic levels are compared. Similarities were found between the hydrocarbons of herbivorous insects, their host plants, and their predators or parasitoids.     

Transport of lipids from high and low density lipoproteins via scavenger receptor-BI.

The scavenger receptor-BI (SR-BI) delivers sterols from circulating lipoproteins to tissues, but the relative potency of individual lipoproteins and the transported cholesterol has not been studied in detail. In this study, we used Chinese hamster ovary cells that express recombinant mouse SR-BI but have no functional low density lipoprotein (LDL) receptors (ldlA7-SRBI cells) to compare the fate of lipids transferred from high or low density lipoproteins to cells by SR-BI. HDL and LDL were equally effective in mediating the transfer of [(3)H]cholesterol to cells. Only 5% of the free cholesterol transferred to cells was esterified, in direct contrast to the findings in the cells that express LDL receptors in which 50% of the transported cholesterol was esterified. Almost all the free cholesterol transferred from lipoproteins to cells was rapidly excreted when the ldlA7-SRBI cells were switched to media containing unlabeled lipoproteins. SR-BI expression was associated with an increase in selective cholesteryl ester uptake from both lipoproteins, but HDL was a more effective donor. HDL and LDL were equally effective in delivering cholesterol to the intracellular regulatory pool via SR-BI. These data indicate that SR-BI is able to exchange cholesterol rapidly between lipoproteins and cell membranes and can mediate the uptake of cholesteryl esters from both classes of lipoproteins.     

昆虫的雌雄嵌合现象

探讨了昆虫雌雄嵌合体的类型、类群、发生机制、对昆虫生物学的影响 ,以及其在胚胎发育学、比较形态学、神经系统调控机理上的应用。并对 1 980～ 2 0 0 0年《动物学记录》中收入的雌雄嵌合体记录进了行整理 ,共发现 1 3目 69科昆虫有雌雄嵌合体记载。文中还整理了中国现有的雌雄嵌合体记录     

Corazonin in insects

Corazonin is a peptidergic neurohormone of insects that is expressed in neurosecretory neurons of the pars lateralis of the protocerebrum and transported via nervi corporis cardiaci to the storage lobes of the corpora cardiaca. This peptide occurs with a single isoform in all insects studied so far, with the exception of the Coleoptera in which no corazonin form could be detected. Very few modifications of [Arg(7)]-corazonin, originally isolated from cockroaches, are known, namely [His(7)]-corazonin which is expressed in certain locusts and the stick insect Carausius morosus, and [Thr(4), His(7)]-corazonin recently described from the honey bee Apis mellifera. In this study, we performed a comprehensive screening for corazonin in the different insect groups after detecting of a fourth isoform in a crane fly, Tipula sp. ([Gln(10)]-corazonin). [Arg(7)]-corazonin is distributed in most major lineages of insects, and is thus the ancient form which was present at the time the phylum Insecta evolved. The replacement of Arg with His at position 7 from the N-terminus occurred several times in the evolution of insects. The third isoform, [Thr(4), His(7)]-corazonin, seems to be restricted to bees (Apidae); whereas wasps (Vespidae) and a bumble bee (Apidae) express other corazonins, specifically [His(7)]-corazonin and [Tyr(3), Gln(7), Gln(10)]-corazonin, respectively. A novel corazonin form, [His(4), Gln(7)]-corazonin, was also detected in all South African members of the newly described insect order Mantophasmatodea. The [His(4), Gln(7)]-corazonin separates these species from the Namibian Mantophasmatodea which express [Arg(7)]-corazonin and can be used as a distinct character to distinguish these morphologically similar insects.     

Flightlessness in insects

The evolution of wings is heralded as the most important event in the diversification of insects, yet flight-wing loss has occurred in nearly all pterygote insect orders. Flight loss is especially prevalent among taxa inhabiting historically stable habitats. Recent studies of wing-polymorphic species have revealed numerous selective trade-offs in the reproductive potentials of winged versus flightless forms. A diverse set of environmental factors, both biotic and abiotic, trigger flight loss in alary polyphenic taxa, presumably by influencing juvenile hormone titers. Phylogenetic comparisons promise to elucidate much about the historical contexts and consequences of flight loss.     

Cognition in insects

A traditional view of cognition is that it involves an internal process that represents, tracks or predicts an external process. This is not a general characteristic of all complex neural processing or feedback control, but rather implies specific forms of processing giving rise to specific behavioural capabilities. In this paper, I will review the evidence for such capabilities in insect navigation and learning. Do insects know where they are, or do they only know what to do? Do they learn what stimuli mean, or do they only learn how to behave?     

昆虫的肢体自残现象

该文主要就昆虫的肢体自残现象发生的种类和虫态、被残器官和部位、自残发生的原因、自残对昆虫个体的有利及不利影响进行了综述，并简单地讨论了肢体自残现象在进化上的意义。     

昆虫的微孢子虫病

介绍了昆虫微孢子虫病的病理学、传播途径、寄主特异性、病害管理以及利用昆虫微孢子虫作为生物杀虫剂的应用等方面的研究进展 ,以期为益虫微孢子虫病害的防治和昆虫微孢子虫杀虫剂的研制提参考。     

Cognition in insects

A traditional view of cognition is that it involves an internal process that represents, tracks or predicts an external process. This is not a general characteristic of all complex neural processing or feedback control, but rather implies specific forms of processing giving rise to specific behavioural capabilities. In this paper, I will review the evidence for such capabilities in insect navigation and learning. Do insects know where they are, or do they only know what to do? Do they learn what stimuli mean, or do they only learn how to behave?