Ultrastructure of the Malpighian Tubule Cells in the Mosquito Larvae, Anopheles sinesis

Ultrastructure of epithelial cells constituting the Malpighian tubule of Anopheles sinesis last instar larvae was observed with electron microscope. Malpighian tubule consists of four long and narrow tubule structures with principal cells in typical absorptive cells and regenerative cells forming the simple epithelium. Apical plasma membrane of the principal cell is differentiated into microvilli with one mitochondrion in each microvilli. Basal plasma membrane had extreme infolding to form a canaliculi and a well developed mitochondria was attached in the infoldings. And, rER, ribosomes, and vacuoles were well developed inside the cells. However, there were two main cell types depending on the differentiation of cell organelles. Type 1 cell was cubic, forming the distal portion of Malpighian tubule. The length of microvilli was approximately 4 μm and the basal infoldings were introjected to the depth of 2 μm inside the cell. On the other hand, Type II cell that formed the main proxinal portion was a low squamous type cells with shorter 2 μm of microvilli and the basal infoldings were introjected to the depths of 4 μm inside the cell. As for vacuoles scattered inside the cells, they were regularly observed in both Type I and II and the Type II cells had better developed cellular organelles. Although regenerative cells were extremely small, their cellular organelles were developed and their overall electron density was high that they appeared darker than the principal cells.     

Synthesis and processing of mammalian protamines and transition proteins

Mouse and rat seminiferous tubule fragment cultures were used to examine synthesis and processing of mammalian protamines and transition proteins. The tubule fragments were incubated with [³H]-arginine, [³H]-histidine, [³⁵S]-cysteine, or [³²P]-PO₄, and radiolabeled proteins were analyzed by acid/urea polyacrylamide gel electrophoresis and fluorography or autoradiography. Newly synthesized protamines were recovered from sonication-resistant nuclei (SRN) and could not be detected in cytoplasmic fractions, indicating that protamines are deposited into nuclei immediately after synthesis. Newly synthesized mouse protamine 1 (mP1) and the precursor to mouse protamine 2 (pre-mP2) migrated more slowly during electrophoresis than their predominant testicular forms, identified by staining with Coomassie blue R-250. Within 1 hour of synthesis, the electrophoretic mobilities of mP1 and pre-mP2 increased to match those of their predominant forms. These changes are consistent with initial charge-neutralizing modifications of the newly synthesized protamines, followed by removal of at least some of the modifying ligands, to unmask protamine basicity. Steady-state phosphorylation rates were high for rat protamine 1 (rP1) and were independent of phosphate content; both rP1 molecules of low and high phosphate content were rapidly phosphorylated. Pre-mP2-3, a major processing intermediate derived by proteolysis of pre-mP2, was also rapidly phosphorylated. Like the protamines, transition protein 2 (TP2) was rapidly phosphorylated and increased in electrophoretic mobility soon after synthesis. In contrast, transition protein 1 (TP1) was not phosphorylated and did not exhibit multiple electrophoretic forms. © 1994 Wiley-Liss, Inc.     

Diuretic activity of Mas-DP II,an identified neuropeptide from Manduca sexta: An in vivo and in vitro examination in the adult moth

Mas-DP II, a recently identified 30 amino acid diuretic peptide isolated from the tobacco hornworm moth, Manduca sexta, was tested for its ability to increase fluid excretion in adult M. sexta, and for the ability to elevate the rate of fluid secretion from isolated Malpighian tubules cultured in vitro. Mas-DP II was found to increase fluid weight loss from decapitated adult moths in a dose-dependent manner; weight loss increased significantly at doses as low as 5 ng for female moths and 25 ng for male moths. Male moths injected with large doses of Mas-DP II continued to exhibit increased rates of fluid loss up to 4 h post-injection. In vitro, Mas-DP II stimulated fluid secretion from isolated Malpighian tubules at concentrations as low as 4 nM for tubules from both male and female moths. © 1994 Wiley-Liss, Inc.     

Electron microscopy and X-ray microanalysis of a halophilic leptospire

The morphology of cells of strain Muggia, a slightly halophilic leptospire, was examined by the negative staining technique.The ultrastructure of the cells was rather similar to that of cells of Leptonema illini, i. e. the cells possessed cytoplasmic tubules. The basal complex of their flagella, however, was similar to the corresponding part of flagella on Gramnegative bacteria. The interior of the cells was densely packed with inclusions, except for the two outermost wavelengths at each end where these inclusions were absent.X-ray microanalysis showed that the inclusions contained sodium and chlorine as their main constituents. The inclusions disappeared upon storage of the cultures at room temperature.     

Ultrastructural changes in the gut and the Malpighian tubules of Epilachna varivestis after application of the new antibiotic Nikkomycin involve an osmoregulatory defect

The effect of the antibiotic Nikkomycin was investigated on the Malpighian tubules and the gut of fourth-instar larvae of the Mexican bean beetle, Epilachna varivestis. Within the Malpighian tubules, three different stages in cell alterations can be recognized. A stage of increased activity (Stage A), and two stages of dedifferentiation (Stages B and C) which are distinguishible by characteristic mitochondrial morphology. In Stage C individuals, when Malpighian tubule function stops entirely, alterations in the midgut take place, that are signs of increased activity. Measurements of hemolymph osmotic pressure showed that there is a considerable increase to a higher level which is maintained. Compared with the ultrastructural data, the regulation of osmotic pressure on a higher level may, in part, be the result of compensation for the failure of Malpighian tubule function by the midgut.     

The ultrastructure of the larval malpighian tubules of a saline-water mosquito

The larval Malpighian tubules of the saline-water mosquito Aedes taeniorhynchus were examined using light and electron microscopy. The tubules contain two cell types: primary cells and stellate cells. Primary cells are characterized by their size (70 μm × 70 μm × 10 μm) and an abundance of intracellular membranebound crystals. Two types of microvilli are found on the luminal surface of the primary cells: (1) small microvilli containing core microfilaments and extensions of endoplasmic reticulum, and (2) larger microvilli (≈3 μm in length) which in addition to the above components contain a mitochondrion along their entire length. Both microvillar types have abundant knobs lining the cytoplasmic surface of the microvillar membrane. These knobs, which are often found in insect ion transporting tissues, have been termed ‘portasomes’ by Harvey (1980). The possible role of these structures in ion transport and mitochondrial positioning is discussed. The stellate cells are much smaller than the primary cells, and lack intracellular crystals. Their microvilli are smaller as well (≈0.6 μm in length) and contain no endoplasmic reticulum. mitochondria or knobs. The cells types found in the saline-water mosquito larva, Aedes taeniorhynchus, are identical to those found in Aedes aegypti, indicating that the unique capacity of saline-water mosquito larvae to transport Mg²⁺ and SO₄|post|staggered|2− is not associated with the presence of an additional cell type.     

Malpighian tubules of larval Aedes aegypti are hormonally stimulated by 5-hydroxytryptamine in response to increased salinity

Two environmental parameters, feeding status and salinity, are expected to affect water and ion balance of the aquatic larvae of Aedes aegypti. Evidence was obtained for regulation of Malpighian tubule fluid secretion rates in response to changes in each of these parameters. Exposure to increased salinity induces release into the hemolymph of material with diuretic effects on Malpighian tubules. Diuretic material is present in hemolymph of larvae raised in higher salinities, rapidly appears in the hemolymph of larvae following transfer from dilute water to higher salinity, and rapidly disappears from the hemolymph following transfer from higher salinity to dilute water. Feeding status affects diuretic properties of both hemolymph and Malpighian tubules. Feeding causes hemolymph to become diuretic relative to hemolymph from nonfeeding larvae. Malpighian tubules removed from feeding larvae have greater basal fluid secretion rates and also appear to have greater maximal fluid secretion capacity than do tubules removed from nonfeeding larvae. Larval hemolymph [5-HT] was found to increase fivefold in response to elevated salinity but was unaffected by feeding status. Methiothepin, a 5-HT receptor antagonist, inhibited stimulation of fluid secretion by 5-HT and blocked the diuretic effects of hemolymph from larvae exposed to higher salinity but was without effect on stimulation of fluid secretion by diuretic peptide. During the course of this investigation, a preliminary pharmacological characterization of the 5-HT receptor on Aedes Malpighian tubules, suggesting that this receptor may be pharmacologically distinct from other described insect 5-HT receptors, was obtained. Arch. Insect Biochem. Physiol. 34:123–141, 1997. © 1997 Wiley-Liss, Inc.     

Sperm structure and spermiogenesis in Coletinia sp. (Nicoletiidae, Zygentoma, Insecta) with a comparative analysis of sperm structure in Zygentoma

The spermatozoon of Coletinia sp. has a bilayered acrosome, a short nucleus (4 microm) and a relatively short sperm tail with two mitochondrial derivatives. The chromatin is uniformly dense except for several electron-lucid channels or strands which permeate the nucleus and which originate in the spermatid as invaginations of the nuclear envelope. The invaginations occur mostly or exclusively along two meridians of the spermatid that are also characterized by the presence of a longitudinal rod of medium electron density. The two rods (designated as 'mid-spermatid rods') evidently are instrumental in the formation of the electron-lucid channels. The significance of this elaborate system of intranuclear channels is not understood. The sperm tail has a 9 + 9 + 2 axoneme with each of the nine microtubular doublets accompanied by an accessory microtubule; scant intertubular material can also be distinguished. Hence, the tail axoneme resembles that of many pterygote insects. Each of the two mitochondrial derivatives contains a crystalline inclusion that has periodically spaced layers going in different directions on either side of the midline. Two synapomorphic traits appear to be shared by Ateluridae and Nicoletiidae, namely the invaginations of the nuclear membrane along two meridians of the nucleus and the shape of the crystalline inclusions of the mitochondrial derivatives. Four species from the family Lepismatidae were also examined as to their sperm ultrastructure. Three of them, Allacrotelsa kraepelini, Ctenolepisma longicaudata and Ctenolepisma sp., were found to be very similar to the two previously examined lepismatids, Thermobia domestica and Lepisma saccharina. On the other hand, spermatozoa of Tricholepisma aurea were aggregated in small groups rather than pairwise joined as seen in the other lepismatids. Sperm characters are also used to reconstruct a phylogenetic hypothesis which suggests a close relationship between Ateluridae and Nicoletiidae.     

In vitro formation of the endoplasmic reticulum occurs independently of microtubules by a controlled fusion reaction

We have established an in vitro system for the formation of the endoplasmic reticulum (ER). Starting from small membrane vesicles prepared from Xenopus laevis eggs, an elaborate network of membrane tubules is formed in the presence of cytosol. In the absence of cytosol, the vesicles only fuse to form large spheres. Network formation requires a ubiquitous cytosolic protein and nucleoside triphosphates, is sensitive to N-ethylmaleimide and high cytosolic Ca(2+) concentrations, and proceeds via an intermediate stage in which vesicles appear to be clustered. Microtubules are not required for membrane tubule and network formation. Formation of the ER network shares significant similarities with formation of the nuclear envelope. Our results suggest that the ER network forms in a process in which cytosolic factors modify and regulate a basic reaction of membrane vesicle fusion.