Sclerotin and lipid in the waterproofing of the insect cuticle

In all the cuticles studied waterproofing is effected by extracuticular material, a mixture of sclerotin precursors and lipids, exuded from the tubular filaments of the pore canals. In Rhodnius larval abdomen it is a layer of thickness similar to the outer epicuticle, believed to be composed of 'sclerotin' and wax, in Schistocerca larval sternal cuticle and in Carausius sternal cuticle it is similar. In Tenebrio adult sternal cuticle of the abdomen, in both the extracuticular exudation and the contents of the distal endings of the tubular filaments, the wax component is obscured by hard 'sclerotin'. In Manduca larva a very thin layer of 'sclerotin' and wax is covered by an irregular wax layer, average 0.75 micron, twice the thickness of the inner epicuticle. In Periplaneta and Blattella the abdominal cuticle is covered by a soft waxy layer, often about 1 micron thick, which is mixed with argentaffin material. Below this is a very thin waterproof layer of wax and 'sclerotin' continuous with the contents of the tubular filaments, which is readily removed by adsorptive dusts. In Apis adult abdominal terga free wax plus sclerotin precursors form a thin layer which is known to be removed by adsorptive dusts. In Calliphora larva there is a very thin layer of the usual mixed wax and sclerotin and below this a thick (0.5 micron) layer, lipid staining and strongly osmiophil, likewise extracuticular and exuded from the epicuticular channels. This material (which is often called 'outer epicuticle') has the same staining and resistance properties as the true outer epicuticle on which it rests. In the abdomen of Calliphora adult the waterproofing wax-sclerotin mixture forms a thin layer over the entire cuticle including the surface of the microtrichia. There is also a thin detachable layer of free wax on the surface.     

Structure of the cuticle of the common house cricket with reference to the location of lipids

Cuticle segments from the thorax, abdomen, and jumping legs of the house cricket. Acheta domesticus, were examined using histological techniques for light microscopy, scanning and transmission electron microscopy, and direct examination of frozen-fractured cuticle. The surface of untreated cuticle is covered by a lipid film which obscures fine surface detail. Standard EM preparative procedures, as well as washing the cuticle with ethanol before examination, remove this film exposing previously covered openings to dermal gland ducts and wax canals. An epicuticle, exocuticle, mesocuticle, endocuticle, and a deposition layer were present in all transverse sections of cuticle. Light microscopy showed that the exocuticle and mesocuticle are heavily impregnated with lipids, whereas there is little lipid associated with the endocuticle. Frozen-fractured cuticle clearly shows the ‘plywood’ structure of the meso- and endocuticle, while the exocuticle fractures as if it were a solid sheet. The epicuticle is composed of a dense homogeneous layer, cuticulin, outer epicuticle, and the outer membrane. Superficial wax was detected only in cuticle samples prepared using vinylcyclohexane dioxide as a polar dehydrant. The results were used to construct a comprehensive model of the cuticle of A. domesticus.     

Glycosyl transfer to an acceptor lipid from insects.

Insect extracts were found to contain a lipid which becomes glycosylated when incubated with uridine diphosphate glucose or uridine diphosphate N-acetylglucosamine and microsomal enzymes of rat liver. The behaviour of the lipid on column or thin-layer chromatography and its stability to acid were equal to those of dolichol monophosphate. The glycosylated compounds were acid labile. Treatment with alkali of the acetylglucosaminyl compound produced a substance that migrated like a hexose phosphate on electrophoresis and that liberated acetylglucosamine on treatment with alkaline phosphatase. The behaviour of the insect glucosylated lipid on thin-layer chromatography and its stability to phenol were similar to dolichol monophosphate glucose and different from ficaprenyl monophosphate glucose. It is concluded that the insect glycosyl acceptor lipid is an α saturated polyprenyl phosphate.     

昆虫中的核输出现象

核质转运是真核细胞生命活动重要的组成部分,细胞核内蛋白的平衡及转录出的RNA出核成熟过程都依赖于核输出,核输出与真核生物的生命活动密切相关;病原物在侵染昆虫时也会利用宿主的核输出机制干扰宿主的免疫反应或劫持宿主的核输出蛋白以利于病毒的组装及复制.本文主要介绍真核细胞中核输出的基本机制、蚊子和果蝇等模式昆虫中核输出通路;...     

Ultrastructural shape and three-dimensional organization of the intracuticular canal systems in the mineralized cuticle of the green crab Carcinus maenas

Two main self-contained canal systems are present in the crab mineralized cuticle. The first, or fibre canal system, is constituted by simple, unbranched vertical canals containing axially running fibres in close association with myoepidermal junctions. The second, or pore canal system, is composed of procuticular pore canals and epicuticular channels that prolong the procuticular canals. In opposition to widespread opinion, pore canals make up a three-dimensional branched system extending from the apical plasma membrane of the epidermis up to the epicuticle. Branching occurs by projections of lateral horizontal from the vertical canals at the lower level of the pigmented layer and by innumerable ramifications of epicuticular canals. In agreement with Neville's model for insects, vertical procuticular pore canals of crustacean mineralized cuticle, and also fibre canals, exhibit a twisted ribbon structure reflecting the helicoidal arrangement of the horizontal chitin-protein microfibrils.     

昆虫糖脂代谢研究进展

肥胖症和糖尿病的日趋流行已经成为世界范围内的公共健康问题,其病因主要在于体内血糖/血脂含量升高引起的能量代谢紊乱。大量的证据表明,昆虫可以作为研究人类代谢疾病的理想模型,它不仅能合成与哺乳动物同源的糖脂代谢相关激素(如胰岛素样肽和脂动激素),而且还具有进化保守的代谢信号通路(如雷帕霉素靶蛋白信号通路)及相关器官与组织(如中肠和脂肪体)。本文主要介绍了昆虫糖脂代谢的过程与调控机制,重点涉及脂肪体和绛色细胞的生理功能、胰岛素样肽/脂动激素对血糖的拮抗调节、参与营养物质代谢的胰岛素-胰岛素样生长因子信号通路以及与类固醇激素合成相关的胆固醇代谢等内容,并结合最新研究成果对黑腹果蝇Drosophila melanogaster糖脂代谢相关基因及其功能进行了总结,以期为昆虫生理学和人类代谢疾病研究提供参考。     

昆虫对全球气候变暖的响应

过去的100年全球地表平均温度显著上升,全球气候变暖对生物的影响引起世界范围内的广泛关注。和其他生物一样,昆虫也受到了气候变暖的影响,如繁殖发育速度增快、遗传变异、种群多样性降低、分布区扩大、种群爆发、外来入侵、种群灭绝等等。全球变暖引起的昆虫响应对农林业以及人类健康存在潜在风险,因此本文主要从物候、分布区、生长发育及繁殖、形态、行为与生理、分子水平这些方面综述全球气候变暖背景下昆虫如何响应,并讨论了目前研究动态和未来的研究方向,意在为气候变化条件下昆虫科学管理策略(如种群监控、模型预测、风险评估、遗传多样性、抗性遗传等)提供指导意义。     

昆虫造血作用和造血干细胞研究进展

昆虫血细胞（insect hemocyte）在昆虫代谢、 发育变态以及先天免疫等方面承担着重要的作用。昆虫只有先天免疫系统, 血细胞所行使的免疫功能对于昆虫对抗外源病菌尤为重要。本文主要介绍了昆虫血细胞类型、 造血作用、 造血干细胞及造血相关因子的相关研究。通过特殊染色和形态学观察, 果蝇Drosophila血细胞主要由3类细胞组成, 而鳞翅目等大部分昆虫血细胞由5类细胞组成。昆虫血细胞主要存在于循环血液环境及造血器官内, 而在这两个系统中都存在有进行复制的血细胞, 这为研究昆虫造血干细胞特性和其定位提供了一个很好的系统。果蝇血细胞祖细胞来自于胚胎中胚层细胞, 然后再分化为各种血细胞, 这一系列分化过程由造血因子所调控。     

A set of possible sensory system preserved in cuticle of Late Devonian thylacocephalan arthropods from Poland

The cuticle of concavicarids (Arthropoda: Thylacocephala) from the early Famennian (Upper Devonian) of the Holy Cross Mountains, Poland was studied with respect to its microstructural details. Investigated laminated cuticle with phosphatic/organic composition, possesses two different kinds of microstructure with assumed sensory functions. The first kind consists of circular depressions, each located in the central area of characteristic polygons forming the carapace exterior ornamentation. These depressions are interpreted as sealed during phosphatisation processes setal lumens. The second kind occurs exclusively in carapace margins. These intracuticular microstructures occur as elongated tubular structures, circular to oval in cross section, penetrating the cuticle interior but not reaching its surface. They form a thin belt with a kind of ‘sensory fields’ on the dorsum and a wider belt in the ventrocaudal part of the carapace. These belts are connected in the rostral and caudal area, forming a continuous sensory zone encompassing each valve. These structures are very similar to crustacean organule canals, and the dorsally situated ‘sensory fields’, suggest some similarity to crustacean sensory dorsal organs. This possible sensory system is the oldest of this kind found in Thylacocephala. Its morphology and presumed canal walls mineralogical composition suggests crustacean affinity of Thylacocephala.     

The supply of oxygen to the flight muscles of insects: A Theory of tracheole physiology

In the flight muscles of insects, virtually every mitochondrion is in contact with or is encircled by terminal tracheoles which reach them by following the channels formed by the invaginated plasma membrane of the muscle fibres, the T-system tubules. In Musca, Calliphora and Drosophila (Diptera), Apis (Hymenoptera) and Tenebrio (Coleoptera) the terminal tracheoles are smooth-surfaced tubes with a lumen of about 50 nm. In Pieris (Lepidoptera) the terminal tracheoles occupy the regular transverse tubular system which runs between the mitochondria and across the fibrils on either side of the H zone. They are smooth tubules of 80–200 nm diameter. Preliminary observations suggest the same arrangement in Ischnura (Odonata). In Rhodnius and other Hemiptera the transverse T-tubule system forms large cavities among the mitochondria: these cavities in Rhodnius are occupied by smooth-walled tracheole endings. In the mature adult of Schistocerca (Orthoptera) T-tubules of varying size are utilized by terminal tracheoles (diameter 50–100 nm). The terminal tracheoles of the flight muscles are highly permeable to myrcene and kerosine. They commonly fill with liquid during rest and this liquid is resorbed during activity. It is suggested that these adaptations increase the efficiency of respiration in the flight muscles by ensuring that, when it is most needed, gaseous oxygen extends to the surface of the mitochondria, from which it is separated by a very permeable barrier.     

Design of an insect cuticle associated with osmoregulation: the porous plates of chloride cells in a mayfly nymph

In mayfly nymphs of the genus Coloburiscoides, cell complexes with an osmoregulatory function (so-called chloride cells) are found in the integuments of the oral gills, the abdominal gills and gill filaments, the coxae and the thoracic sternites. The cuticle overlying each cell complex is a rigid circular plate which is known to be porous to colloidal lanthanum suspensions. The present study shows that the plate is composed only of the cuticulin and dense layers of the epicuticle. Both layers have substructures built of subunits on almost perfect hexagonal lattices. The lattice spacings are 53 and 9.5 nm for the dense layer and the cuticulin layer respectively. During moulting the apical plasma membrane of the chloride cell remains adpressed to the old porous plate. The new porous plate is formed from a new chloride cell which intrudes from the base of the integument. Throughout the moult small pores persist in the new and otherwise continuous cuticle to allow continuity of the cytoplasm of the apical and basal portions of the old chloride cell. It is thought that this phenomenon allows osmoregulatory function of the chloride cell complex to be maintained during the moult.     

Changes in the mechanical properties of the extensible cuticle of Rhodnius through the fifth larval instar

The ultimate tensile strength (σ_UT) and the modulus of elasticity (E) of Rhodnius extensible cuticle are σ_UT = 2.20 × 10⁷ Nm^?2, E = 2.43 × 10⁸ Nm^?2 (unplasticised); σ_UT = 1.43 × 10⁷ Nm^?2, E = 9.45 × 10⁶ Nm^?2 (plasticised with 5HT) and σ_UT = 9.05 × 10⁶ Nm, E = 2.46 × 10⁶ Nm^?2 (plasticised in pH 5 buffer).The mechanical properties of cuticle from insects which have deposited additional layers of cuticle after they have been fed differ from those of cuticle from unfed insects. This is possibly due to the different composition of the additional cuticle: it is suggested that the post-feeding cuticle is providing protection and a template for the next instars cuticle.The maximum strain of extensible cuticle from starved insects is related to the amount of matrix protein present.     

A PCR method for detection of plant meals from the guts of insects

The feeding behaviour of insects is a difficult ecological interaction to study. To date, entomologists have used biochemical and molecular techniques to identify the meals of predatory insects. We present here a molecular approach to identifying the DNA of plant species in the insect gut using the ribulose bisphosphate carboxylase gene large subunit (rbcL). A reference collection of 23 plant species from the southern Jordan Valley, Israel, was genetically characterized and employed. Insects belonging to eight different families were collected in the field along with the plants upon which they were found. After collection and prior to analysis, these insects were isolated on the plants they were found upon in the laboratory. This was to ensure that the insects had only one plant meal in their gut, as multiple plant meals would require additional techniques like cloning. A blind study was performed, genetically confirming plant DNA to species level from the processed gut contents of the insects. All reference plant species could be differentiated using a 157 bp long fragment of the rbcL gene. Plant DNA was identifiable, and the meal of the respective insect was accurately determined in each case. Analyses using experimentally fed crickets, Gryllodes hebraeus, determined that plant DNA was still detectable by PCR up to 12 h post-ingestion. This research proposes the application of molecular techniques for the identification of herbivorous insect feeding behaviour to increase understanding of plant–insect interactions.     

Cuticulogenesis correlated with ultrastructural changes in oenocytes and epidermal cells in the late cockroach embryo

During late embryogenesis in a cockroach, the epidermal cells secrete two cuticles: the embryonic cuticle and the pharate first larval cuticle. Late embryogenesis begins with the deposition of the cuticulin layer of the embryonic cuticle. The embryonic cuticle is an atypical one. It remains relatively thin and a well lamellated endocuticle is usually lacking. After general apolysis of the embryonic cuticle the epidermis secretes the epicuticle of the first larval cuticle and, subsequently, a typical lamellate procuticle. During the penultimate phase of late embryogenesis (i.e. before general apolysis) the epidermis becomes larvally committed. Some epidermal cells start to differentiate into specialized structures of the dermal glands, whereas the differentiated oenocytes appear to have acquired some stability. Nevertheless, shortly before general apolysis some oenocytes display signs of an increased alteration of the SER. When general apolysis occurs, the oenocytes contain a well-developed SER. The whole of the oenocyte population is programmed to regress after epicuticle deposition of the first larval cuticle. The correlation of oenocyte regression with available data on cuticulogenesis, ecdysteroid titres and cuticular lipid synthesis is discussed.     

The all-or-none rule in morphogenetic action of juvenile hormone on insect epidermal cells

We have investigated ultrastructural changes in the integuments of larval–adult and larval–pupal intermediates produced by exogenous application of juvenile hormone (JH) analogues in Pyrrhocoris apterus (Hemiptera), and Galleria mellonella and Manduca sexta (Lepidoptera). Ultrastructural analysis of the epidermis of these intermediates always revealed the presence of only two types of epidermal cell, which produced morphologically perfect cuticles of the previous and future developmental stages. There were no intermediate cuticles at the level of individual cells. It has been determined that a single epidermal cell constitutes the lowest elementary unit in the perception and realization of the developmental messages conveyed by JH to its target tissues. Further investigations revealed that the responses of individual epidermal cells to JH were strictly autonomous and qualitative, i.e. they were executed according to the ''yes-or-no'' or ''all-or-none'' rule. The neighbouring epidermal cells could realize independently, side-by-side, the quite dissimilar +JH (somatic growth) or -JH (metamorphosis) developmental programmes, although each of them formed biochemically, functionally, and ontogenetically different structures. The qualitative on- and off- signal given by JH for induction of the stationary (+JH) developmental cycle was limited to relatively short, genetically determined, and stage-specific developmental periods of cellular susceptibility to JH. The mosaic mixtures of the heterochronic, larval–pupal or adult epidermal cells, which we found in different proportions on the bodies of the intermediates, revealed two variable, development-related factors: (i) the presence or absence of a minimum effective concentration of JH, and (ii) positive or negative sensitivity of a particular epidermal cell to JH.     

Feeding modulation in insects through factors in the hemolymph

In insect hemolymph, many factors are present that can influence feeding motivation, such as lipids, carbohydrates, and other metabolites. Levels of these hemolymph factors fluctuate according to metabolic, nutrient and feeding states, eventually affecting feeding motivation and consequent regularly occurring feeding cycles. Such fluctuations contribute to energy homeostasis and innate feeding behavior in insects possibly by endocrine systems. Ultimately, orchestration of bioactive factors in the hemolymph modulate feeding motivation and nutrient selective behavior in insects.