Lipophorin of female Blattella germanica (L.): characterization and relation to hemolymph titers of juvenile hormone and hydrocarbons

High density lipophorin (HDLp) from the hemolymph of the German cockroach, Blattella germanica (L.) (Family Blattellidae), has an apparent molecular weight of 670kDa, with an isoelectric point of 7.0 and a density of 1.109g/ml. It is composed of two subunits, apolipoprotein-I (212kDa) and apolipoprotein-II (80kDa), and consists of 51.4% lipid, 46.2% protein and 2.4% carbohydrate. Hydrocarbons constitute 42.2% of the total lipids which also contain diacylglycerol, cholesterol and phospholipid. Lipophorin is rich in the amino acids glutamic acid, aspartic acid, lysine, valine, and leucine. Specificity of a polyclonal antibody was demonstrated by Western blotting and Ouchterlony immunodiffusion: the antiserum recognized native HDLp and apolipoprotein-I, but not apolipoprotein-II, purified vitellin, or other hemolymph proteins. It also recognized a protein in the hemolymph of Supella longipalpa (Blattellidae) but did not cross-react with hemolymph proteins from Periplaneta americana (Blattidae) or Diploptera punctata (Blaberidae). An enzyme-linked immunosorbent assay was developed to measure the HDLp titer in the hemolymph of adult females. The titer of HDLp, a juvenile hormone binding protein, exhibited no clear relationship to the changing titer of juvenile hormone in hemolymph. The hemolymph titer of hydrocarbon, which is also carried by HDLp, showed some functional relation to the concentration of HDLp in the hemolymph. Because it concurrently serves multiple functions in insect development and reproduction, lipophorin titer might covary with the titers of lipid ligands that occur at high concentrations and require extensive shuttling through the hemolymph.     

Insect lipophorin conversions. Compositional analysis of high- and low-density lipophorin of Acherontia atropos and Locusta migratoria.

The formation of low-density lipophorin (LDLp) in insect hemolymph, resulting from association of high-density lipophorin (HDLp) with both lipid and apolipophorin III, is considered to provide a reutilizable lipid shuttle for flight muscle energy supply. The changes in lipid and apolipoprotein composition of LDLp, isolated after flight activity, compared to that of HDLp in the hemolymph at rest, were studied in two evolutionary divergent insects, the hawkmoth Acherontia atropos and the migratory locust, Locusta migratoria. Using FPLC on Superose 6 prep grade as a novel technique to separate the apolipophorins of HDLp and LDLp, the ratio of apolipoprotein I, II, and III in HDLp of both species was demonstrated to be 1:1:1, whereas flight activity resulted in a ratio of 1:1:10 in LDLp. Injection of adipokinetic hormone into resting moths showed that, depending on the dose, the number of apolipophorin III molecules in LDLp can exceed that recovered after the physiological condition of flight. Analysis of the lipophorin lipids demonstrated that in addition to the considerable increase in diacylglycerol in the LDLp particle, which is consistent with the role LDLp in energy supply, particularly the hydrocarbons were increased compared to HDLp, rendering the mechanism of LDLp formation from HDLp even more complex.     

Hydrocarbon circulation and colonial signature in Pachycondyla villosa

In ants, both cuticular and postpharyngeal gland (PPG) hydrocarbons (HCs) have been involved in nestmate recognition. However, no detailed comparison is available. A comparative study including also high density lipophorin (HDLp), an internal HC carrier, was therefore undertaken on Pachycondyla villosa. Purified HDLp is an 820 kDa lipoprotein with a density of 1.114 g/ml and two 245 and 80 kDa apo-proteins. Its hydrocarbon profile is very similar with the cuticular one, in agreement with its hydrocarbon carrier function. Conversely, n-alkanes and externally branched monomethylalkanes are markedly decreased in the PPG. According to their physical properties, this suggests that they are involved in waterproofing on the cuticle. The PPG actually contains only internally branched mono-, dimethylalkanes or monomethylalkenes; their greater fluidity is more adequate for chemical communication. The percentages of some of them are statistically not different between the cuticle and PPG. Their mixtures vary with colonies and they may thus be involved in colonial signature. A scheme for hydrocarbon circulation is discussed, involving lipophorin, cuticle, PPG and self-grooming in one individual, a pathway complementary or alternative to the selective delivery by lipophorin in some other insects. HCs are then distributed between nestmates' cuticles through allo-grooming and physical contacts.     

Transport of a hydrophobic biosynthetic precursor by lipophorin in the hemolymph of a geometrid female moth which secretes an epoxyalkenyl sex pheromone

Previous experiments with a geometrid species, Ascotis selenaria cretacea, have suggested that a pheromonal C19 3,4-epoxy-6,9-diene is biosynthesized from the corresponding 3,6,9-triene produced outside a pheromone gland and transported to it via hemolymph after association with lipophorin. In order to clarify this transport, high-density lipophorin (HDLp) in the female moths showing two bands (apoLp I with ca. 250 kDa and apoLp II with ca. 80 kDa) on an SDS-PAGE was purified by KBr equilibrium density-gradient ultracentrifugation, and the association of the triene was confirmed by GC-MS analysis of a solvent extract from the isolated protein. Next, the role of HDLp was revealed by a topical application of the deuterated trienyl precursor to the abdomens of the females. The trienyl precursor was associated with HDLp. In their pheromone glands, the triene and the deuterated epoxy pheromone were detected, indicating movement of the triene via the hemolymph. Experiments with male moths of A. s. cretacea and female moths of Bombyx mori showed the same association of HDLp with the triene topically applied. This result suggested that the adult females of A. s. cretacea did not develop HDLp specialized in the triene transport. Furthermore, the topical application of a mixture including the trienyl precursor and two other related hydrocarbons showed equal amounts of association by HDLp but selective delivery of the precursor to pheromone glands in the A. s. cretacea females.     

Lipid transfer particle catalyzes transfer of carotenoids between lipophorins of Bombyx mori

The yellow color of Bombyx mori hemolymph is due to the presence of carotenoids, which are primarily associated with lipophorin particles. Carotenoids were extracted from high density lipophorin (HDLp) of B. mori and analyzed by HPLC. HDLp contained 33 μg of carotenoids per mg protein. Over 90% of carotenoids were lutein while -carotene and β-carotene were minor components. When larval hemolymph was subjected to density gradient ultracentrifugation, a second minor yellow band was present, which was identified as B. mori lipid transfer particle (LTP). During other life stages examined however, this second band was not visible. To determine if coloration of LTP may fluctuate during development, we determined its concentration in hemolymph and compared it to that of lipophorin. Both proteins were present during all life stages and their concentrations gradually increased. The ratio of lipophorin: LTP was 1015:1 during the fourth and fifth instar larval stages, and 2030:1 during the pupal and adult stages. Thus, there was no correlation between the yellow color attributed to LTP and its hemolymph concentration. It is possible that yellow coloration of the LTP fraction corresponds to developmental stages when the particle is active in carotene transport. To determine if LTP is capable of facilitating carotene transfer, we took advantage of a white hemolymph B. mori strain which, when fed artificial diet containing a low carotene content, gives rise to a lipophorin that is nearly colorless. A spectrophotometric, carotene specific, transfer assay was developed which employed wild type, carotene-rich HDLp as donor particle and colorless low density lipophorin, derived from the white hemolymph strain animals, as acceptor particle. In incubations lacking LTP carotenes remained associated with HDLp while inclusion of LTP induced a redistribution of carotenes between the donor and acceptor in a time and concentration dependent manner. Time course studies suggested the rate of LTP-mediated carotene transfer was relatively slow, requiring up to 4 h to reach equilibrium. By contrast, studies employing ³H-diacylglycerol labeled HDLp as donor particle in lipid transfer assays revealed a rapid equilibration of label between the particles. Thus, it is plausible that the slower rate of LTP-mediated carotene transfer is due to its probable sequestration in the core of HDLp.     

Lipid transfer particle in locust hemolymph: purification and characterization

A lipid transfer particle (LTP) from the hemolymph of adult male locusts, Locusta migratoria, was isolated and purified. The locust LTP exhibited its capacity to catalyze the exchange of diacylglycerol between low density lipophorin (LDLp) and high density lipophorin (HDLp). Contrary to the LTP reported for the tobacco hornworm, M. sexta, the locust LTP appeared to lack the capacity to promote net transfer of diacylglycerol to form an intermediate density lipophorin, although it seems premature to conclude the complete lack of such a capacity in locust LTP. The original concentration of LTP in hemolymph is assumed to be extremely low compared to that of lipophorin; only a catalytic amount of LTP may be present in the hemolymph (e.g., only 160 micrograms of LTP was obtained from the original hemolymph containing 400 mg protein). The molecular weight of intact LTP was estimated to be about 600,000 and the LTP was comprised of three glycosylated apoproteins, apoLTP-I (mol wt 310K), apoLTP-II (mol wt 89K), and apoLTP-III (mol wt 68K). The locust LTP contained significant amounts of lipids; the total lipid content amounted to 14.4% and the lipids were comprised of 17% hydrocarbons, 44% diacylglycerol, 8% cholesterol, 13% free fatty acid, and 18% phospholipids. The above molecular properties of locust LTP are essentially similar to those reported for M. sexta LTP.     

Lipophorin levels in the yellow fever mosquito,Aedes aegypti,and the effect of feeding

High density lipophorin (HDLp) is the major lipid transport vehicle in insect hemolymph. Using an indirect ELISA, levels of HDLp were measured in the yellow fever mosquito, Aedes aegypti. The level of lipophorin, when normalized to the total weight of the insect, was similar in the different developmental stages. Starvation (access to water only) of adult females did not affect the level of HDLp nor its density when compared to sugar-fed females. On the other hand, blood feeding (of normally sugar-fed females) resulted in a three-fold increase of the HDLp level at 40 h after feeding. This increase was accompanied by a slight but significant increase in the density of HDLp at 24 h after feeding. Ingestion of a lipid-free protein meal or a lipid-supplemented protein meal induced changes in HDLp level and density that were comparable to those induced by ingestion of a blood meal. Ingestion of a blood meal, following starvation (access to water only) from the moment of adult emergence, did not induce an increase in HDLp level. The results presented indicate that, in contrast to other insect species, A. aegypti responds to an increased need for lipid transport in the hemolymph by increasing the amount of HDLp. Arch. Insect Biochem. Physiol. 34:301–312, 1997. © 1997 Wiley-Liss, Inc.     

Lipophorin receptor regulates the cuticular hydrocarbon accumulation and adult fecundity of the pea aphid Acyrthosiphon pisum

Cuticular hydrocarbons form a barrier that protects terrestrial insects from water loss via the epicuticle. Lipophorin loads and transports lipids, including hydrocarbons, from one tissue to another. In some insects, the lipophorin receptor (LpR), which binds to lipophorin and accepts its lipid cargo, is essential for female fecundity because it mediates the incorporation of lipophorin by developing oocytes. However, it is unclear whether LpR is involved in the accumulation of cuticular hydrocarbons and its precise role in aphid reproduction remains unknown. We herein present the results of our molecular characterization, phylogenetic analysis, and functional annotation of the pea aphid (Acyrthosiphon pisum) LpR gene (ApLpR). This gene was transcribed throughout the A. pisum life cycle, but especially during the embryonic stage and in the abdominal cuticle. Furthermore, we optimized the RHA interference (RNAi) parameters by determining the ideal dose and duration for gene silencing in the pea aphid. We observed that the RNAi-based ApLpR suppression significantly decreased the internal and cuticular hydrocarbon contents as well as adult fecundity. Additionally, a deficiency in cuticular hydrocarbons increased the susceptibility of aphids to desiccation stress, with decreased survival rates under simulated drought conditions. Moreover, ApLpR expression levels significantly increased in response to the desiccation treatment. These results confirm that ApLpR is involved in transporting hydrocarbons and protecting aphids from desiccation stress. Furthermore, this gene is vital for aphid reproduction. Therefore, the ApLpR gene of A. pisum may be a novel RNAi target relevant for insect pest management.     

Lipophorin transport of hydrocarbon during early vitellogenesis in the silkworm,Bombyx mori

Lipophorin transports the hydrophobic molecule from origin to destination in time specific manner. Here, we investigate the hydrocarbon composition in the lipophorin during day 2 of pupal silkworm, Bombyx mori. Lipophorin was isolated from hemolymph by immunoprecipitation; lipid extracted and analyzed in GC-MS, resulting in seventeen compounds including eight hydrocarbons. Which were searched with the Pherobase (Pheromone database) and functional roles analysed. All hydrocarbons denoted as a pheromone except pentatriacontane in lepidopteron insects. Other hand, hydrocarbons such as hexadecane, nonadecane, undecane and hexacosane specifically refer as an attractant, additionally heptacosane, octacosane and docosane indicate as an allomone in non-lepidopteron insects. As well as, docosane and undecane perform as kairomone. Identified pheromone interaction with lipophorin was analysed by molecular docking and shows the best binding score. All hydrocarbons bound in a lipid binding pocket, most of these sharing the same binding sites for hydrophobic interaction and hydrogen bonding. Overall findings elucidated that lipophorin associated with different hydrocarbons by hydrogen bonds and hydrophobic interactions, and each of the hydrocarbon having various functional roles.     

Lipophorin receptor-mediated lipoprotein endocytosis in insect fat body cells

High-density lipophorin (HDLp) in the circulation of insects is able to selectively deliver lipids to target tissues in a nonendocytic manner. In Locusta migratoria, a member of the LDL receptor family has been identified and shown to mediate endocytosis of HDLp in mammalian cells transfected with the cDNA of this receptor. This insect lipophorin receptor (iLR) is temporally expressed in fat body tissue of young adult as well as larval locusts, as shown by Western blot analysis. Fluorescence microscopy revealed that fat body cells internalize fluorescently labeled HDLp and human receptor-associated protein only when iLR is expressed. Expression of iLR is down-regulated on Day 4 after an ecdysis. Consequently, HDLp is no longer internalized. By starving adult locusts immediately after ecdysis, we were able to prolong iLR expression. In addition, expression of the receptor was induced by starving adults after down-regulation of iLR. These results suggest that iLR mediates endocytosis of HDLp in fat body cells, and that expression of iLR is regulated by the demand of fat body tissue for lipids.     

The molecular and metabolic essentials for long-distance flight in insects

Summary The mechanism of long-distance flight in insects was investigated by comparing lipid mobilization and transport in gregarious- and solitary-phase locusts and in the American cockroach. Unlike the gregarious-phase locust, both the American cockroach and the solitary locust were unable to form low-density lipophorin (loaded with increased amount of diacylglycerol) even when injected with adipokinetic hormone (AKH). The cockroach fat body responded to AKH. However, not only does the American cockroach lack apolipophorin-III (apoLp-III) in the haemolymph, but the fat body contains only an extremely small amount of diacylglycerol and a relatively large triacylglycerol pool. By contrast, the solitary-phase locust had apoLp-III in the haemolymph, but the fat body was only one-seventh or less in weight of the fat body of the gregarious locust. Furthermore, the fat body of the solitary locust contains a very small amount of triacylglycerol (1/20 or less of that of the gregarious locust) with only a trace of diacylglycerol. It was concluded that in the American cockroach and the solitary locust, the stores of fuel in the fat body are insufficient to maintain prolonged flight.Abbreviations AKII adipokinetic hormone - apoLp-III apolipophorin III - HDLp high-density lipophorin - LDLp low-density lipophorin - LTP lipid transfer particle - MW molecular weight - SDS-PAGE sodium dodecyl sulphate-polyacrylamide gel electrophoresis     

Biosynthesis and secretion of insect lipoprotein.

Biosynthesis of high density lipophorin (HDLp) was studied in larvae and adults of the migratory locust, Locusta migratoria. In an in vitro system, fat bodies were incubated in a medium containing a mixture of tritiated amino acids. Using SDS-PAGE and immunoblotting, it was shown that larval and adult fat bodies secreted both HDLp apoproteins, apolipophorin I (apoLp-I) and apolipophorin II (apoLp-II). Radiolabel was recovered in both apoproteins, indicative of de novo synthesis. The density of the fractions containing the apoproteins synthesized and secreted by larval and adult fat bodies was determined by density gradient ultracentrifugation. A radiolabeled protein fraction was found at density 1.12 g/ml. Using an enzyme-linked immunosorbent assay for detecting apoLp-I and apoLp-II, it was demonstrated that both apoproteins were present in this fraction, which had a density identical to that of circulating HDLp in hemolymph. Lipid analysis revealed that it contained phospholipid, diacylglycerol, sterol, and hydrocarbons. From these results it is concluded that the fat body of the locust synthesizes both apoLp-I and apoLp-II, which are combined with lipids to a lipoprotein particle that is released into the medium as HDLp.     

Wax moth,Galleria mellonella fat body receptor for high-density lipophorin (HDLp)

To identify and characterize the HDLp (high-density lipophorin) receptor from Galleria mellonella (LpRGm), we used techniques of ligand blotting. This method was, to our knowledge, first used to characterize the lipophorin receptor (LpR) in insects. LpRGm had an approximate molecular weight of 97 kDa under non-reducing conditions and bound the HDLp specifically. The time-course of lipophorin binding to their receptor protein was rapid. The binding of lipophorins to their receptors was saturable with a Kd of 34.33+/-4.67 microg/ml. Although Ca2+ was essentially required in the binding of HDLp to their receptors, interestingly increasing concentration of Ca2+ has shown to have a slight inhibitory effect. EDTA was used here as Ca2+ chelating reagent, because Mg2+ in the binding buffer did not affect the binding of HDLp to their receptors, and inhibited the binding of HDLp and LpRGm absolutely. Suramin (polysulfated polycyclic hydrocarbon), known to inhibit the binding of lipoproteins to their receptors, effectively abolished the binding of HDLp to their receptors. LpRGm showed the stage specific binding activity especially in day 1-3 last instar larval, prepupal, and day 1-3 adult stages.     

Binding of juvenile hormone III to lipophorin from the american cockroach Periplaneta americana

Whole hemolymph from the American cockroach, Periplaneta americana, efficiently binds juvenile hormone (JH) III and to a lesser extent JH-I and 10, 11-epoxyfarnesyl diazoacetate (EFDA). The dissociation constants for racemic JH-III and EFDA are 30 ± 2 nM and 1.0 μM, respectively. Isolated lipophorin also binds [³H]JH-III and to a lesser extent JH-I. Other proteins from the hemolymph do not bind JH-III. Binding of JH-III to lipophorin is enantioselective. The dissociation constant, measured with a 92% 10R and 8% 10S mixture, is 21 ± 2 nM. Each lipophorin molecule contains one specific binding site for JH-III. It is concluded that lipophorin is the JH-III-specific transport protein in the hemolymph of the American cockroach. By a combination of photoaffinity labelling and gradient electrophoresis with sodium dodecyl sulphate on polyacrylamide gel, we showed that the JH-III-specific binding site is probably located on apolipophorin I.     

Acetate Synthesis from H(2) plus CO(2) by Termite Gut Microbes

Gut microbiota from Reticulitermes flavipes termites catalyzed an H(2)-dependent total synthesis of acetate from CO(2). Rates of H(2)-CO(2) acetogenesis in vitro were 1.11 +/- 0.37 mumol of acetate g (fresh weight) h (equivalent to 4.44 +/- 1.47 nmol termite h) and could account for approximately 1/3 of all the acetate produced during the hindgut fermentation. Formate was also produced from H(2) + CO(2), as were small amounts of propionate, butyrate, and lactate-succinate. However, H(2)-CO(2) formicogenesis seemed largely unrelated to acetogenesis and was believed not to be a significant reaction in situ. Little or no CH(4) was formed from H(2) + CO(2) or from acetate. H(2)-CO(2) acetogenesis was inhibited by O(2), KCN, CHCl(3), and iodopropane and could be abolished by prefeeding R. flavipes with antibacterial drugs. By contrast, prefeeding R. flavipes with starch resulted in almost complete defaunation but had little effect on H(2)-CO(2) acetogenesis, suggesting that bacteria were the acetogenic agents in the gut. H(2)-CO(2) acetogenesis was also observed with gut microbiota from Prorhinotermes simplex, Zootermopsis angusticollis, Nasutitermes costalis, and N. nigriceps; from the wood-eating cockroach Cryptocercus punctulatus; and from the American cockroach Periplaneta americana. Pure cultures of H(2)-CO(2)-acetogenic bacteria were isolated from N. nigriceps, and a preliminary account of their morphological and physiological properties is presented. Results indicate that in termites, CO(2) reduction to acetate, rather than to CH(4), represents the main electron sink reaction of the hindgut fermentation and can provide the insects with a significant fraction (ca. 1/3) of their principal oxidizable energy source, acetate.     

Sites of Synthesis and Transport Pathways of Insect Hydrocarbons: Cuticle and Ovary as Target Tissues

SYNOPSIS. The outer surface of insects is covered with a lipidlayer that provides water-proofing and protection against environmentalstresses. Hydrocarbons (HC) are major constituents of this epicuticularwax and they also serve as semiochemicals. In some insects HCare also exploited as biosynthetic precursors for pheromones.HC are synthesized by oenocyteswhich are situated in the integumentor hemocoel. Shuttling of HC to the epicuticie, fat body, andgonads requires transport through an aqueous medium. Insects,unlike vertebrates, use a versatile lipoprotein to effect lipidtransport and to selectively deliver lipids to specific tissues.A high-density hemolymph lipoprotein (lipophorin [Lp]) servesthis function.In adult females of the German cockroach (Blattellagermanica), Lp carries both HC and a contact sex pheromone.Lipophorin is a multi-functional lipid carrier serving alsoas a juvenile hormone binding protein in many insects. Studiesofthe interactions between Lp and HC are beginning to unravelthe routes used in delivering HC to target tissues. We discussthepathways and dynamics of loading of Lp with HC and HC-derivedpheromones, their transport through the hemolymph, and depositionin various tissues, including the epicuticie, ovaries, and pheromone-emittingglands.     

Flight metabolism in Panstrongylus megistus (Hemiptera: Reduviidae): the role of carbohydrates and lipids

The metabolism of lipids and carbohydrates related to flight activity in Panstrongylus megistus was investigated. Insects were subjected to different times of flight under laboratory conditions and changes in total lipids, lipophorin density and carbohydrates were followed in the hemolymph. Lipids and glycogen were also assayed in fat body and flight muscle. In resting insects, hemolymph lipids averaged 3.4 mg/ml and significantly increased after 45 min of flight (8.8 mg/ml, P < 0.001). High-density lipophorin was the sole lipoprotein observed in resting animals. A second fraction with lower density corresponding to low-density lipophorin appeared in insects subjected to flight. Particles from both fractions showed significant differences in diacylglycerol content and size. In resting insects, carbohydrate levels averaged 0.52 mg/ml. They sharply declined more than twofold after 15 min of flight, being undetectable in hemolymph of insects flown for 45 min. Lipid and glycogen from fat body and flight muscle decreased significantly after 45 min of flight. Taken together, the results indicate that P. megistus uses carbohydrates during the initiation of the flight after which, switching fuel for flight from carbohydrates to lipids.     

Identification of Phe-Gly-Leu-amide type allatostatin-7 in Reticulitermes flavipes: its localization in tissues and relation to juvenile hormone synthesis

The allatostatins (ASTs), with a Tyr/Phe-Xaa-Phe-Gly-Leu/Ile-amide C-terminus, are neuropeptides that occur in many orders of insects, but are known to inhibit juvenile hormone (JH) synthesis by corpora allata (CA) only in cockroaches, crickets, and termites. 5 AST peptides with similar sequences to those of 6 species of cockroaches have been isolated and sequenced from extract of brain tissue of the termite Reticulitermes flavipes. The amino acid sequence of a 6th peptide, R. flavipes AST-7, determined by LC-MS/MS following HPLC fractionation of brain extract, is S-P-S-S-G-N-Q-R-L-Y-G-F-G-L-NH(2). The 8 terminal amino acids are identical to AST-7 of the cockroach Diploptera punctata. R. flavipes and D. punctata AST-7s inhibited JH synthesis by CA of both species equally and their affinity for antibody against D. punctata AST-7 is similar. Immunoreactivity of termite tissue with this antibody indicates neuro- and myomodulatory activity of the peptide in addition to its demonstrated allatostatic function. The density of AST immunostaining in axons within the CA of R. flavipes and the rate of JH synthesis by similar glands were negatively correlated. This is evidence that when AST is abundant in the glands it is being released in vivo to limit JH production.     

白蚁表皮碳氢化合物组分鉴定及分类学意义

应用GC-MS分析表明,不同种类白蚁表皮碳氢化合物组成和含量均有差异。运用UPGMA聚合R分析的最小距离系数值绘制的系统树表明：圆唇凸额类白蚁——黄胸散白蚁Reticulitermes flaviceps、双色散白蚁R. dichrous和R. sp.1之间;圆唇平额类白蚁——圆唇散白蚁R. labralis、小头散白蚁R. microcephalus、R. sp.2和R. sp.3之间; 尖唇类白蚁——海南异白蚁Heterotermes hainanensis、拧黄异白蚁H. citrinus、细颚异白蚁H.leptomandibularis、尖唇异白蚁H. aculabialis和H. sp. 4之间的亲缘关系较近。3类白蚁中,圆唇凸额类白蚁和圆唇平额类白蚁亲缘关系相近,而两者与尖唇类白蚁亲缘关系较远。实验结果表明,我国存在异白蚁属,它与散白蚁属主要区别在于其表皮缺乏以下数种碳氢化合物：正十七烷烃、正二十烷烃、正二十一烷烃、正二十二烷烃、正二十三烷烃、正二十四烷烃和正二十六烷烃等;却含有一种特殊化合物异喹啉。表皮碳氢化合物分析的结果与形态分类的结果有一定差异,形态分类被鉴定为双色散白蚁的R. sp.1,被鉴定为小头散白蚁的R. sp.2,被鉴定为圆唇散白蚁的R.sp.3,被鉴定为尖唇散白蚁的H. sp.4,根据表皮碳氢化合物分析的结果,R. sp.1、R. sp.3和H. sp.4可能是其他种,而R. sp.2则可能是圆唇散白蚁的亚种或其他种。     

Alternative lipid mobilization: The insect shuttle system

Lipid mobilization in long-distance flying insects has revealed a novel concept for lipid transport in the circulatory system during exercise. Similar to energy generation for sustained locomotion in mammals, the work accomplished by non-stop flight activity is powered by oxidation of free fatty acids (FFA) derived from endogenous reserves of triacylglycerol. The transport form of the lipid, however, is diacylglycerol (DAG), which is delivered to the flight muscles associated with lipoproteins. In the insect system, the multifunctional lipoprotein, high-density lipophorin (HDLp) is loaded with DAG while additionally, multiple copies of the exchangeable apolipoprotein, apoLp-III, associate with the expanding particle. As a result, lipid-enriched low-density lipophorin (LDLp) is formed. At the flight muscles, LDLp-carried DAG is hydrolyzed and FFA are imported into the muscle cells for energy generation. The depletion of DAG from LDLp results in the recovery of both HDLp and apoLp-III, which are reutilized for another cycle of DAG transport. A receptor for HDLp, identified as a novel member of the vertebrate low-density lipoprotein (LDL) receptor family, does not seem to be involved in the lipophorin shuttle mechanism operative during flight activity. In addition, endocytosis of HDLp mediated by the insect receptor does not seem to follow the classical mammalian LDL pathway.Many structural elements of the lipid mobilization system in insects are similar to those in mammals. Domain structures of apoLp-I and apoLp-II, the non-exchangeable apolipoprotein components of HDLp, are related to apoB100. ApoLp-III is a bundle of five amphipathic -helices that binds to a lipid surface very similar to the four-helix bundle of the N-terminal domain of human apoE. Despite these similarities, the functioning of the insect lipoprotein in energy transport during flight activity is intriguingly different, since the TAG-rich mammalian lipoproteins play no role as a carrier of mobilized lipids during exercise and besides, these lipoproteins are not functioning as a reusable shuttle for lipid transport. On the other hand, the deviant behavior of similar molecules in a different biological system may provide a useful alternative model for studying the molecular basis of processes related to human disorders and disease.