Cellular organization and ferritin uptake in the mid-gut epithelium of a moth,Ephestia kühniella

Aspects of fine structure and function of the subcommissural organ of the embryonic chick

The fine structure of the subcommissural organ (SCO) of the embryonic chick has been studied. No evidence of secretory release was obtained. The SCO seems not to be involved in such previously suggested roles as water regulation or response to varying light cycles. The introduction of electron dense markers into the 3rd ventricle demonstrated rapid and massive uptake into coated pits and coated vesicles of the ependymal cells and its subsequent incorporation into terminal bodies. It is suggested that the uptake of macromolecules from the cerebrospinal fluid may be an important and hitherto unsuspected function of the SCO.

Ultrastructure of the copper-accumulating region of the Drosophila larval midgut

The copper-accumulating region of the midgut is a mosaic of interstitial and cup-shaped, copper-accumulating cells. The cup of each cuprophilic cell is lined with a highly refractile border of long microvilli except in one strain where it is predominantly lamellar. The nucleus lies basally; the basal plasma membrane is fairly extensively infolded. Cytolysomes are abundant and increase in number with increasing copper content of the diet. The interstitial cells bear short, less regular microvilli and have a less electron-dense cytoplasm. The nucleus is apical, the mitochondria-associated basal membrane is very extensively infolded and cytolysomes are less abundant. Virus-like particles present in nuclei of both cell types increase in number with increasing copper concentration.

The impact of the Bacillus subtilis SPB1 biosurfactant on the midgut histology of Spodoptera littoralis (Lepidoptera: Noctuidae) and determination of its putative receptor

SPB1 is a Bacillus subtilis strain producing a lipopeptide biosurfactant. The insecticidal activity of this biosurfactant was evaluated against the Egyptian cotton leaf worm (Spodoptera littoralis). It displayed toxicity with an LC(50) of 251 ng/cm(2). The histopathological changes occurred in the larval midgut of S. littoralis treated with B. subtilis SPB1 biosurfactant were vesicle formation in the apical region, cellular vacuolization and destruction of epithelial cells and their boundaries. Ligand-blotting experiments with S. littoralis brush border membrane vesicles showed binding of SPB1 biosurfactant to a protein of 45 kDa corresponding to its putative receptor. The latter differs in molecular size from those recognized by Bacillus thuringiensis Vip3A and Cry1C toxins, commonly known by their activity against S. littoralis. This result wires the application of B. subtilis biosurfactant for effective control of S. littoralis larvae, particularly in the cases where S. littoralis will develop resistance against B. thuringiensis toxins.

Proteolysis, histopathological effects, and immunohistopathological localization of δ-endotoxins of Bacillus thuringiensis subsp. kurstaki in the midgut of lepidopteran olive tree pathogenic insect Prays oleae

Considering the fact that Prays oleae is one of the most pathogenic insects to the olive tree in the Mediterranean basin, particularly in Tunisia, the mode of action of Cry insecticidal toxins of Bacillus thuringiensis kurstaki in Prays oleae midgut was investigated. The proteolysis of Bacillus thuringiensis delta-endotoxins in the midgut was a key step in determining their potency against Prays oleae. The latter's proteases activated the delta-endotoxins early, yielding stable toxins. The in vitro and in vivo binding of these toxins to Prays oleae larvae midgut was studied immunohistochemically, evidencing a midgut columnar cell vacuolization, microvilli damage, and then a pass of epithelium cell content into the larvae midgut. Moreover, Bacillus thuringiensis toxins were shown to bind to the apical microvilli of the midgut epithelial cells. The in vitro study of the interaction of Prays oleae midgut proteins with biotinylated Bacillus thuringiensis toxins allowed the prediction of four suitable receptor proteins in Prays oleae.

The larval midgut of Anticarsia gemmatalis (Hübner) (Lepidoptera: Noctuidae): light and electron microscopy studies of the epithelial cells

The morphology of the midgut epithelium cells of Anticarsia gemmatalis (Hübner) larvae is described by light and transmission electron microscopy. The midgut of A. gemmatalis is the largest portion of the digestive tract, with three distinct regions: proximal, media and distal. Its wall is formed by pseudostratified columnar epithelial tissue having four cell types: columnar, goblet, regenerative, and endocrine cells. The columnar cells are numerous and long, with the apical portion showing many lengthy microvilli and the basal portion invaginations forming a basal labyrinth. The goblet cells have a large goblet-shaped central cavity delimited by cytoplasmic projections filled with mitochondria. The regenerative cells present electron-dense cytoplasm and few organelles. The endocrine cells are characterized by electron-dense secretory granules, usually concentrated in the cytoplasm basal region.

Nucleopolyhedrovirus interactions with their insect hosts

It is clear from this brief review that our understanding of the molecular cross-talk between insects and their baculovirus pathogens is still very limited. Studies in cell culture have taught us a great deal about the basic baculovirus molecular machinery and how it is regulated, and in many cases this information has been predictive of what occurs in infected insects. Frequently, however, studies in cell culture do not adequately predict the infection process in insect hosts, as demonstrated by viral mutants (some of which were discussed in this review) that behave identically to wild-type virus in cell culture but differ markedly in larvae. More baculovirus studies, therefore, need to be conducted in vivo if we are to improve our understanding of the complex interactions between baculoviruses and their hosts. Conducting baculovirus studies in insects (or at least in primary cell culture) also offers the opportunity to address questions that reach beyond the baculovirus community in significance. For example, almost all of our knowledge of viral fusion mechanisms comes from infection of cells in culture where the pH is neutral or acidic and the temperature is constant at 27 degrees or 37 degrees C. An answer to the question of how the ODV envelope fuses with the microvillar membrane of columnar epithelial cells in the highly alkaline midgut environment at low temperatures will not only be important for an improved understanding of baculovirus infection in the natural world, but will also constitute a new chapter on viral entry mechanisms. Similarly, the answer to the question of how baculovirus nucleocapsids move basally within microvilli promises to involve factors and/or a mechanism not yet described by cell biologists, and so will constitute a valuable contribution to both baculovirology and cell biology. There are many more such examples of biological mechanisms that can be uniquely explored within the context of baculoviruses and their insect hosts, some of which have been highlighted in this review. As more and more young investigators realize the importance of combining a knowledge of virology, molecular technology, and insect biology, however, many of the outstanding mysteries will be solved.

Effect of sublethal Bacillus thuringiensis crystal endotoxin treatment on the larval midgut of a moth, Manduca: SEM study

The effect of a single, sublethal dose of B. thuringiensis crystal endotoxin on the midgut of the moth Manduca sexta larvae was monitored during acute and recovery stages. Initially both goblet and columnar cells swelled. Many columnar cells produced membrane extrusions. In some cases the affected cells ruptured, extruding cellular debris into the midgut lumen. Following the acute stage, the midgut tissue recovered, the damaged cells being extruded into the midgut lumen apparently as newly regenerated cells rose to take their place. The insects appeared to recover completely and continue normal development.

Passage of hemolysins through the midgut epithelium of female Ixodes ricinus L. fed on rabbits infested or reinfested with ticks

Antibodies considered in this study are hemolysins synthesized by rabbits against sheep red blood cells. Ingested with the blood meal, they cross the tick midgut epithelium and retain their immunological properties in the hemolymph. During a reinfestation of rabbits, more ticks present these antibodies, and titres are generally higher than during a first infestation. Hemolysins are only found in ticks weighing 180 mg or more.

The induction and distribution of an insect ferritin--a new function for the endoplasmic reticulum

Three insect tissues have particular roles as filters to maintain the fluid composition of the hemolymph. Water and ions enter and leave through the midgut. The pericardial cells filter circulating hemolymph. Malpighian tubules, often with the rectum, allow resorption from a hemolymph filtrate that passes to the hindgut. All three tissues have plasma membrane infolds making a reticulum on their hemolymph surfaces, and all three have RER leading to SER extensions into their reticula. SER is a catch-all description for membranes lacking ribosomes in the pre-Golgi complex set of compartments of the vacuolar system. Some kinds of SER are well known for their role in housing enzymes for steroid metabolism and for detoxification. The SER ramifying within the plasma membrane reticular systems of tissues concerned with hemolymph filtration contains ferritin, suggesting that this SER has another, different function. In contrast to vertebrate cells, where ferritin is confined to the cytosol and lysosomes, we have found that in Calpodes and perhaps in most insects, ferritin occurs in the vacuolar system and not in the cytosol. Ferritin occurs naturally in the RER and SER of cells at the hind end of the midgut, in pericardial cells and in the yellow region of the Malpighian tubules. Additional ferritin is induced by loading the gut or hemolymph with iron. Overloading with iron causes ferritin secretion to the gut lumen. We propose that the SER in these cells functions in iron homeostasis by holding ferritin for loading and unloading as it moves to and from the reticulum at the cell surface where it can be maximally exposed to extracellular fluid flow.

The morphology and fine structure of the larval midgut of a moth (Manduca sexta) in relation to active ion transport

Light and electron microscopic examination of the midgut of Manduca sexta has shown that the organization of this tissue is more complex than was originally believed. The midgut can be divided into anterior, middle and posterior regions on the basis of the pattern of folding of the epithelial sheet, and variations in the structure of goblet and columnar cells which occur along its length. The columnar cells show gradual structural changes form the anterior to the posterior end of the midgut. For example, the microvilli in the anterior region form a dense, interconnecting network from which vesicles break off. This organization becomes less obvious through the middle region, until by the posterior region each microvillus is unconnected to adjacent microvilli along its entire length and vesicles are no longer produced. Two distinct types of goblet cells are found. In the anterior and middle regions the goblet cells have a large basally located cavity, but in the posterior region the cavity occupies only the apical half of the cell. In both cases the cavity is formed by invagination of the apical membrane, which is studded with small particles implicated in active ion transport. In the anterior and middle regions this membrane is closely associated with mitochondria, but not in the posterior region. The significance of the observed structural differences is discussed in relation to active ion transport.

Midgut ultrastructure of Culex tarsalis (Diptera: Culcidae) before and after a bloodmeal

The midgut ultrastructure of rasin-and blood-fed female mosquitoes, Culex tarsalis Coquillentt, was examined. The raisin-fed midgut is characterized by: (1) large nuclei, (2) small mitochondria, (3) short segments of rough endoplasmic reticulum, (4) rough endoplasmic reticular vesicular vesicles in the posterior midgut only, and (5) increased autophagic acitivity with age. Blood feeding elicits drastic changes in midgut epithelial structures: (1) nuclei are smaller, (2) mitochondria are much enlarged, (3) rough endoplasmic reticular vesicles disappear, (4) rough endoplasmic reticular whorls appear, (5) residual lyosomal figures are abundant, and (6) an intercellular accumulation of an electron-opaque material is noted. The significance of rough endoplasmic reticular whorls and vesicles in bloodmeal digestion is discussed. In addition, the concept of a functional host 'gut barrier' to infection by pathogens is examined as related to a possible by-pass mechanism.

The passage of serum immunoglobulins through the gut of Sarcophaga falculata, Pand

Rabbits were immunized with brain, muscle or haemolymph of adult Sarcophaga falculata, and groups of Sarcophaga were then fed on serum collected from the immune rabbits. Rabbit serum immunoglobulins on the tissues of the fed flies were demonstrated by the indirect fluorescent antibody method, using fluorescent goat-anti-rabbit IgG. The antibodies were specifically demonstrated in the tissues that had been used as immunizing antigen. It was also shown that antibodies unrelated to fly antigens pass through the fly gut and react with the specific antigens.

Morphology and function of Malpighian tubules and associated structures in the cockroach, Periplaneta americana

This paper describes the different regions of the Malpighian tubules and the associated structures (ampulla, midgut, ileum) in the cockroach, Periplaneta americana. There are about 150 tubules in each insect. Each tubule consists of at least three parts. The short distal region is thinner than the other parts and is highly contractile. The middle region comprises most of the tubule length and is composed of primary and stellate cells. Primary cells contain numerous refractile mineral concretions, while stellate cells have smaller nuclei, fewer organelles, simpler brush border, and numerous multivesicular bodies. Symbiont protozoa are sometimes present within the lumen of the middle region near where it opens into the proximal region of the tubule. The latter is a short region that drains the tubular fluid into one of the six ampullae. These are contractile diverticula of the intestine located at the midgut-hindgut junction. The ampulla is highly contractile, and consists of a layer of epithelial cells surrounding a cavity that opens into the gut via a narrow slit lined by cells of unusual morphology. The proximal region of the tubule and the ampulla resemble the midgut in that they have similar micromal origin and reabsorptive function for the proximal region of the tubule and for the ampulla. A number of inclusions found within the tubule cells are described, including peroxisomes and modified mitochondria. Current theories of fluid transport are evaluated with regard to physiological and morphological characteristics of Malpighian tubules. The possible role of long narrow channels such as those between microvilli and within basal folds is considered, as is the mechanism by which these structures are formed and maintained. Also discussed is the role of peroxisomes and symbionts in the excretory process.