Scanning electron microscopy of the posterior spiracles of cattle grubs Hypoderma bovis and Hypoderma lineatum

Posterior spiracles of newly hatched first instar larvae of Hypoderma bovis (L.) and H. lineatum (DeVill.) consist of two pairs of spiracular openings. Each pair is surrounded by a rima bearing three spines. Posterior spiracles of second instar larvae are composed of a pair of medial ecdysial scars bounded laterally by spiracular plates. H. bovis spiracular plates have twenty-nine to forty openings, each surrounded by a slightly raised rima. H. lineatum spiracular plates have eighteen to twenty-five openings. Spiracular openings lead to posterior felt chambers which are connected to a common anterior felt chamber filled with a meshlike network. In third instar H. bovis each medial ecdysial scar is surrounded by a strongly concave spiracular plate. Spiracular openings are surrounded by slightly raised rima. Most rimae bear a spine. Spiracular plates of H. lineatum are flat and rimae are without spines. Each spiracular opening leads to a posterior felt chamber, several of which are confluent with a larger anterior felt chamber. Anterior felt chambers open into the dorsal longitudinal tracheal trunk. Felt chambers in third instar larvae are also filled with a complex mesh.     

Ultrastructure of the foregut and associated glands of Calicotyle kröyeri (Monogenea: Monopisthocotylea)

The mouth, pharynx and oesophagus of Calicotyle are lined by syncytial epithelia, and there are numerous unicellular glands associated with the oesophagus. An infolding of unmodified external tegument lines the mouth cavity and is connected by discrete cytoplasmic processes to subjacent perikarya. It contains two types of secretory body and its luminal surface is invested with a finely filamentous coating. The pharynx and oesophagus are lined by irregularly-folded epithelia that are interconnected by a septate desmosome. Membranous inclusions distinguish the pharynx epithelium and there is a well developed basal lamina for insertion of the pharyngeal muscles. The oesophagus epithelium is perforated by the openings of the oesophageal glands. These lie in the surrounding parenchyma and produce a dense, membrane-bound secretion which is conveyed by duct-like extensions of the glands to the oesophagus lumen. The ducts are supported in places by microtubules and are anchored to the oesophageal epithelium by septate desmosomes. A septate desmosome also marks the junction between the epithelium and the gut caeca.     

细菌素的合成与作用机制

细菌素是由细菌产生的抗菌蛋白,可以杀死与产生菌相近的细菌。很多乳酸菌产生不同多样性的细菌素,虽然这些细菌素都是由发酵或非发酵食品中发现的乳酸菌产生的,但是迄今只有乳酸链球菌素(Nisin)作为食品防腐剂被广泛应用。和抗生素不同的是,细菌素由核糖体合成,需经翻译后修饰活化并且通过特定转运系统输到胞外才能发挥其功能,它一般通过作用于靶细胞膜来抑制靶细胞的生长,同时本身合成细菌素的细胞对其产物具有免疫性。细菌素能安全有效地抑制病原体生长,在食品行业中具有广阔的应用前景。     

Secretion of predicted Inc proteins of Chlamydia pneumoniae by a heterologous type III machinery

Chlamydia spp. are strictly intracellular pathogens that grow inside a vacuole, called an inclusion. They possess genes encoding proteins homologous to components of type III secretion machineries, which, in other bacterial pathogens, are involved in delivery of bacterial proteins within or through the membrane of eukaryotic host cells. Inc proteins are chlamydial proteins that are associated with the inclusion membrane and are characterized by the presence of a large hydrophobic domain in their amino acid sequence. To investigate whether Inc proteins and other proteins exhibiting a similar hydropathic profile might be secreted by a type III system, we used a heterologous secretion system. Chimeras were constructed by fusing the N-terminal part of these proteins with a reporter, the Cya protein of Bordetella pertussis, and these were expressed in various strains of Shigella flexneri. We demonstrate that these hybrid proteins are secreted by the type III secretion system of S. flexneri, thereby providing evidence that IncA, IncB and IncC are secreted by a type III mechanism in chlamydiae. Moreover, we show that three other proteins from Chlamydia pneumoniae, all of which have in common the presence of a large hydrophobic domain, are also secreted by S. flexneri type III secretion machinery.     

Ultrastructure of the jugular body of Rana pipiens

Summary The jugular bodies in adult Rana pipiens, are surrounded by a capsule of mesothelium and connective tissue, and their parenchyma consists of cell cords arranged in a sinusoidal network. The cell cords are formed by irregular reticular cells, showing numerous filaments and joined together by zonulae adhaerents. The intercellular spaces are filled by reticular fibres and free cells. These latter are small and medium lymphocytes, lymphoblasts, and developing and mature plasma cells. Additionally, free macrophages, neutrophils and acidophils also occur. Sinusoidal blood vessels show thin walls with numerous filaments and pinocytotic vesicles. They exhibit a discontinuous basement membrane, and tight junctions frequently occur between endothelial cells. Occasionally, lymphatic vessels are found and the innervation is principally vasomotor, although nerve endings appear remarkably near reticular cells and lymphocytes. The jugular bodies of adult R. pipiens are plasma cell and antibody-forming organs, whose functional significance is discussed in relation to their ultrastructural organization.     

Ultrastructural and histochemical study of the salivary glands of Aplysia depilans (Mollusca, Opisthobranchia)

The digestive system of the sea hare, Aplysia depilans , includes a pair of ribbon-shaped salivary glands. A central duct and a large blood vessel run close to each other along the length of these glands and both are surrounded by a layer of muscle cells. Three cell types form the glandular epithelium: granular cells, vacuolated cells and mucocytes. The granular cells possess cilia and spherical secretion granules, located primarily in the apical region. The granules of immature cells have a low electron density and are mainly formed by neutral polysaccharides with small amounts of proteins. The granules of mature cells are larger, have a high electron density and are mainly formed by proteins with lower amounts of neutral polysaccharides. Transition stages between immature and mature granular cells are observed. The vacuolated cells are large and frequently pyramidal in shape, but after the application of histochemical techniques almost all vacuoles remain uncoloured. The numerous vacuoles contain flocculent material in a clear background and the mitochondria possess large crystalline structures in the matrix. A pyramidal shape is also typical of the mucocytes, which are filled with vesicles containing granular masses surrounded by a network of secretion material. These large cells are strongly stained by Alcian blue, revealing the presence of acidic mucopolysaccharides. This is the first ultrastructural study of the salivary glands in opisthobranch gastropods.     

Purification of neuronal inclusions of patients with Huntington's disease reveals a broad range of N-terminal fragments of expanded huntingtin and insoluble polymers

Huntington's disease resulting from huntingtin containing an expanded polyglutamine is associated with aggregates largely confined to neuronal inclusions, and with neuronal death. Inclusions are thought to originate from discrete N-terminal fragments of expanded huntingtin produced by specific endopeptidases. We have now purified the neuronal inclusions of Huntington's disease brain. When incubated in concentrated formic acid, purified inclusions release a polymer, an oligomer and a broad range of N-terminal fragments of expanded huntingtin. The fragments and the polymeric forms are linked to each other by non-covalent bonds as they are both released by formic acid, whereas the polymeric forms themselves are presumably stabilized by covalent bonds, as they are resistant to formic acid. We also demonstrate the presence in affected areas of the brain but not in unaffected areas of a broad range of soluble N-terminal fragments of expanded huntingtin not yet associated with the inclusions and which are likely to be the precursors of the inclusions. Fragmentation of expanded huntingtin in Huntington's disease must result from the operation of multiple proteolytic activities with little specificity and not from that of a specific endopeptidase; subsequent aggregation of the fragments by covalent and non-covalent bonds leads to the formation of the inclusions.     

Comparative Study of Ultrastructure of Interlamellar and Intralamellar Types of Henneguya exilis Kudo from Channel Catfish*†

SYNOPSIS. The inter- and intralamellar types of Henneguya exilis Kudo (Myxosporida) infections from channel catfish are similar in spore structure and sporogenesis, but differ in the structure of their plasmodium wall and surface coat and in their relationship with the host cells. The 2 clinical types differ also in the sites of development and growth patterns of plasmodia within a gill filament. Interlamellar plasmodia are limited by 2 outer unit membranes which give rise to both single-and double-membraned pinocytic canals. Intralamellar plasmodia are limited by a single outer unit membrane which gives rise to single-membraned pinocytic canals. Interlamellar plasmodia are covered by a fine granular coat of highly variable thicknesses; in some regions there is direct contact between the parasite and cells of the host. There is some evidence that host cell cytoplasm as well as interstitial material are taken in by interlamellar plasmodia. In contrast, intralamellar plasmodia are covered by a fine granular coat of almost uniform thickness, which prevents direct contact between the parasite and cells of the host; probably only interstitial material is taken by these plasmodia.     

Comparative study of ultrastructure of interlamellar and intralamellar types of Henneguya exilis Kudo from channel catfish

The inter- and intralamellar types of Henneguya exilis Kudo (Myxosporida) infections from channel catfish are similar in spore structure and sporogenesis, but differ in the structure of their plasmodium wall and surface coat and in their relationship with the host cells. The 2 clinical types differ also in the sites of development and growth patterns of plasmodia within a gill filament. Interlamellar plasmodia are limited by 2 outer unit membranes which give rise to both single-and double-membraned pincytic canals. Intralamellar plasmodia are limited by a single outer unit membrane which gives rise to single-membraned pinocytic canals. Interlamellar plasmodia are covered by a fine granular coat of highly variable thicknesses; in some regions there is direct contact between the parasite and cells of the host. There is some evidence that host cell cytoplasm as well as interstitial material are taken in by interlamellar plasmodia. In contrast, intralamellar plasmodia are covered by a fine granular coat of almost uniform thickness, which prevents direct contact between the parasite and cells of the host; probably only interstitial material is taken by these plasmodia.     

Localization of the gene-richest and the gene-poorest isochores in the interphase nuclei of mammals and birds

At a resolution of 850 bands, human chromosomes comprise two subsets of bands, the GC-richest H3⁺ and the GC-poorest L1⁺ bands, accounting for about 17 and 26%, respectively, of all bands. The former are a subset of the R bands and the latter are a subset of the G bands. These bands showed the highest and the lowest gene densities, respectively, as well as a number of other distinct features. Here we report that human and chicken interphase nuclei are characterized by the following features. (1) The gene-richest/GC-richest chromosomal regions are predominantly distributed in internal locations, whereas the gene-poorest/GC-poorest DNA regions are close to the nuclear envelope. (2) The interphase chromosomes seem to be characterized by a polar arrangement, because the gene-richest/GC-richest bands and the gene-poorest/GC-poorest bands are predominantly located in the distal and proximal regions, respectively, of chromosomes, and because interphase chromosomes are extremely long. While this polar arrangement is evident in the larger chromosomes, it is not displayed by the chicken microchromosomes and by some small human chromosomes, namely by chromosomes that are almost only composed by GC-rich or by GC-poor DNA. (3) The gene-richest chromosomal regions display a much more spread-out conformation compared to the gene-poorest regions in human nuclei. This finding has interesting implications for the formation of GC-rich isochores of warm-blooded vertebrates.     

Phylogenetic analysis of thoracic structures of Carabidae (Coleoptera: Adephaga)

Thoracic structures of adult carabids were examined and analyzed phylogenetically. Geadephaga excl. Trachypachini are considered as a monohyletic unit based on correlated synapomorphic features of the posterior metathoracic region: the metepimeron is parallel-sided and at right angle to the body axis; the metacoxae do not project beyond the lateral margin of the preepisterum. Gehriniini are nor related to Trachypaciini. The metriine-paussine lineage is characterized as monopkyletic by exceptionally long and fairly broad metepimera. The presence of an elytral flange is considered a snapomorphy of Paussinae. The monophyly of Paussinae excluding My-stropomus is sugesred cy extended elytral epipleura, which cover large parts of the metepimera, and by the parallel body outline. The monohyly of Anisochaeta is not supported by conclusive synapomorphic features of the thorax. Cychrini, Carabini, Nebriini, Opistiini, and Notiohi lini seem to form a monophyletic unit, as suggested by the concealed external lamella of the metepimeron. Cicindelinae, Elaphrini, Loricerini, Migadopini, Rhysodini, and Caraboidea Limbata are considered as a monophletic unit based on the following correlated synapomor-phies: meso ‘sternum’ strongl modiled, hexagonal groove reduced, procoxal cavities closed, aex of prosternal process-redced. Caraboidea Limbata (Jeannel 1941–42) excl. Scrobifera are cgaracterized as a monophyletic group by lobate rnetepimera, and conjunct mesocoxal cavities. Caraboidea Limbata excl. Scrobifera and Stylifera (Jeannel 1941–42 are characterized by narrow meseimera. Masoreimorphi, Callistomorphi, Lebiomorphi and Pseudornorphinae are characterizei by biperforate procoxal cavities. It is quite likely that biperforate procoxal cavities are also a groundplan feature of Brachininae.     

Measurement of surface area of stones

The surface area of stones can be quickly, accurately, and precisely estimated from linear regression equations of area on a two-dimensional term of the form (xy + yz + zx) where x, y, and z are either the axial dimensions or the axial perimeters of stones. Dimension measurements are made with calipers, and perimeters are measured with a tape measure or a mapping wheel. The best fit slopes for the equations are determined from a representative sample of stones whose surface areas are measured by mapping. Estimates of surface areas of river-worn cobbles by these methods had mean percentage absolute errors of about 4%, considerably better than other methods examined.     

Identification of protein-protein interactions using in vivo cross-linking and mass spectrometry

The purification of protein complexes can be accomplished by different types of affinity chromatography. In a typical immunoaffinity experiment, protein complexes are captured from a cell lysate by an immobilized antibody that recognizes an epitope on one of the known components of the complex. After extensive washing to remove unspecifically bound proteins, the complexes are eluted and analyzed by mass spectrometry (MS). Transient complexes, which are characterized by high dissociation constants, are typically lost by this approach. In the present study, we describe a novel method for identifying transient protein-protein interactions using in vivo cross-linking and MS-based protein identification. Live cells are treated with formaldehyde, which rapidly permeates the cell membrane and generates protein-protein cross-links. Proteins cross-linked to a Myc-tagged protein of interest are copurified by immunoaffinity chromatography and subjected to a procedure which dissociates the cross-linked complexes. After separation by SDS-PAGE, proteins are identified by tandem mass spectrometry. Application of this method enabled the identification of numerous proteins that copurified with a constitutively active form of M-Ras (M-Ras(Q71L)). Among these, we identified the RasGAP-related protein IQGAP1 to be a novel interaction partner of M-Ras(Q71L). This method is applicable to many proteins and will aid in the study of protein-protein interactions.     

The fine structure of the ganglia of the guinea-pig trachea

Summary The parasympathetic ganglia of the guinea-pig trachea have been investigated by scanning and transmission electron microscopy. They are covered by a continuous perineurium and connective tissue is found between the neural elements. Blood vessels inside the ganglia have continuous endothelia and are sometimes accompanied by pericytes and a sheath of perineurial cells. Individual neuronal cell bodies and large processes are almost completely covered by a thin layer of satellite cells, except for very small areas that directly face the basal lamina and connective tissue space. Nerve fibres are also completely and individually ensheathed by Schwann cell processes; naked fibres are not found. In some regions of the nerve cell body, there are complex interdigitations between short neuronal processes and satellite cells. Large differences in the size of neurons may indicate the presence of different neuronal populations. Nerve endings containing mainly small clear vesicles are the most common type, and these form synapses on dendrites, but some profiles have many large granular vesicles. These ganglia resemble other parasympathetic, sympathetic and sensory ganglia and not the enteric ganglia. However, an unusual feature of the cytoplasm of the satellite and Schwann cells is the abundance of 10 nm intermediate filaments.     

Adaptive change in the resource-exploitation traits of a generalist consumer: the evolution and coexistence of generalists and specialists

Mathematical models of consumer-resource systems are used to explore the evolution of traits related to resource acquisition in a generalist consumer species that is capable of exploiting two resources. The analysis focuses on whether evolution of traits determining the capture rates of two resources by a consumer species produce one generalist, two specialists, or all three types, when all types are characterized by a common fitness function. In systems with a stable equilibrium, evolution produces one generalist or two specialists, depending on the second derivative of the trade-off relationship. When there are sustained population fluctuations, the nature of the trade-off between the consumer's capture rates of the two resources still plays a key role in determining the evolutionary outcome. If the trade-off is described by a choice variable between zero and one that is raised to a power n, polymorphic states are possible when n > 1, which implies a positive second derivative of the curve. These states are either dimorphism, with two relatively specialized consumer types, or trimorphism, with a single generalist type and two specialists. Both endogenously driven consumer-resource cycles, and fluctuations driven by an environmental variable affecting resource growth are considered. Trimorphic evolutionary outcomes are relatively common in the case of endogenous cycles. In contrast to a previous study, these trimorphisms can often evolve even when new lineages are constrained to have phenotypes very similar to existing lineages. Exogenous cycles driven by environmental variation in resource growth rates appear to be much less likely to produce a mixture of generalists and specialists than are endogenous consumer-resource cycles.     

Development of cell wall appendages inAcanthosphaera zachariasi (Chlorococcales): Kinetics,site of cellulose synthesis and of microfibril assembly,and barb formation

Summary The investigation of the formation of cell wall appendages inAcanthosphaera by means of light and electron microscopy and by the use of dyes which interfere with microfibril assembly resulted in several observations which are helpful to an understanding of the formation of normal cell walls. The barbs are built up in the ER, pass through the Golgi apparatus, and are extruded exocytotically after cytokinesis, a remarkable example of the secretion of a structured product. Each cellulose microfibril in a spike develops in a distinct pit of the plasmalemma. The pits are aggregated in a pit field, generating one spike, and are closely adjacent to a basal vesicle which might have morphogenetic and/or regulatory functions. The pits are the site of cellulose synthesis; here the plasmalemma is conspicuously thickened. As shown directly and by the application of Calcofluor white and Congo red, the microfibrils assemble at a certain distance from the plasma membrane,i.e. cellulose synthesis and microfibril assembly are separated by a gap. It is discussed whether single glucan chains or small bundles of them are released from the plasmalemma. The elongation rate of the spikes indicates that about 1000 glycosidic linkages per glucan chain per minute are formed.     

Inheritance of glutenin protein subunits of wheat

Summary The inheritance of the high-molecular-weight (HMW) glutenin protein subunits in hexaploid wheat has been investigated by using sodium dodecyl sulphate-polyacrylamide gel electrophoresis to examine the segregation of these subunits in 496 test-cross seeds. The parents of the f₁ hybrid were chosen so that the test-cross seeds segregated for all the HMW glutenin bands. Two glutenin subunits from one parent, believed to be controlled by genes on chromosome 1D, segregated as alternatives to two glutenin subunits from the other parent, a result that supports the assumption that these subunits are controlled by allelic genes at each of two loci that are very closely linked. Similar results were obtained for glutenin subunits believed to be controlled by chromosome IB, which suggests that these subunits are controlled also by allelic genes at each of two loci that are very closely linked. A single glutenin subunit band, believed to be controlled by chromosome 1A, segregated as an alternative to a single glutenin band from the other parent, except that one seed did not possess either band. It was concluded that these bands are controlled either by allelic genes or by nonallelic genes that are very closely linked.     

The role of N-glycans in spermatogenesis

Many proteins, in particular those in the plasma membranes, are glycosylated with carbohydrates, which are grouped into O-glycans and N-glycans. O-glycans are synthesized step by step by glycosyltransferases, whereas N-glycans are synthesized by en-bloc transfer of the so-called high-mannose-type oligosaccharide from lipid-linked precursor to polypeptide. The high-mannose-type N-glycans are then modified by processing alpha-mannosidases. Alpha-mannosidase IIx (MX) was identified as the gene product of processing alpha-mannosidase II (MII)-related gene. MX apparently plays subsidiary role for MII in many cell types, as N-glycan patterns of MX null mouse tissues are not altered significantly. Surprisingly MX null male mice are infertile due to a failure of spermatogenesis. This review provides a brief overview of the in vivo role of N-glycans which are revealed by the gene knockout mouse approach, and introduce our studies on the MX gene knockout mouse. The MX gene knockout experiments unveiled a novel function of a specific N-glycan, which is N-acetylglucosamine-terminated and has a fucosylated triantennary structure, in the adhesion between germ cells and Sertoli cells. The study of MX is a good example of how the in vivo roles of an apparently redundant gene product are determined by the gene knockout approach.     

Characterization of the catalytic subunits of the different types of polycation-stimulated protein phosphatases

Three polycation-stimulated (PCSH-, PCSM- and PCSL-) protein phosphatases are characterized by distinct specificities and regulatory properties. The properties of the catalytic subunits obtained from the 3 basic types of PCS phosphatases are apparently identical. The 35 kDa catalytic subunits are insensitive to inhibitor-1 and modulator protein and in contrast with the holoenzymes are less sensitive to stimulation by protamine, displaying a similar degree of stimulation and an identical concentration optimum; preincubation with polycations also results in a time-dependent deactivation. The phosphorylase phosphatase activity of the three catalytic subunits is stimulated to a similar extent by low but comparable concentrations of detergents, but not by metal ions. Upon limited proteolysis by trypsin the basal, but to a lesser extent the polycation-stimulated activity of the holoenzymes and the catalytic subunits is decreased.