Indigenous microflora associated with the tegument of Triaenophorus nodulosus (Cestoda) and the intestine of its pike host

Investigations of the indigenous microflora associated with the mucous intestines of fish and its cestode parasites have been for the first time carried out using the methods of transmission and scanning electron microscopy. New data on the bacterial biodiversity in the cestode and its fish host are obtained. Nanobacteria and spirochaetes are for the first time revealed in a fish host together with the previously known bacteria forming the intestinal microflora of fish. Spirochaetes were shown to be associated with the intestines of a pike host only, while nanobacteria cover abundantly the surface of the apical parts of the intestinal microvilli and the apical parts of the microtriches in the cestode tegument. The similarity of the bacterial floras associated with the apical surface of the parasite tegument and the intestine of the host should be noted. At the same time, deeper bacterial communities represented by obligate symbionts are specific. Thus, there is a normal indigenous microflora in cestodes, associated with the tegumental surface. This symbiotic microflora has specific morphological features and provides the balance of relations in the parasite-host system.     

The karyotypes of Triaenophorus nodulosus and T. crassus (Cestoda: Pseudophyllidea)

Two species of the genus Triaenophorus were found to have widely different chromosome sets. The karyotype of T. nodulosus consists of 26 biarmed chromosomes ranging from 1.45 to 6.75 microns long. The diploid set of T. crassus contains 18 chromosomes with a well-distinguished first pair of large metacentric homologues. All the chromosomes with the exception of the last pair of acrocentric elements are biarmed. Their absolute length ranges from 1.50 to 8.50 microns. The possible pathways of karyotype differentiation and the evolution of these species are discussed.     

Cellular Composition of Parenchyma and Extracellular Matrix in Ontogenesis of Triaenophorus nodulosus (Cestoda)

The cellular composition of parenchyma was studied in the ontogenesis of Triaenophorus nodulosus, and it was shown that the specialized parenchymal cells was absent. The extracellular matrix fibrils were synthesized successively by the tegumental cytons and muscle cells. The coracidium basal matrix consisted of electron-light and electron-dense layers, and the reticular layer appeared at the procercoid stage. Reserve nutrients were accumulated by the musculocutaneous sac elements at the procercoid stage and, later, by the glandular and tegumental cells. It has been proposed that the parenchyma as an independent histological unit is absent, while the parenchymal organization is based on all specialized cellular elements that do not lose their typical features.     

Structure of scolex hooks and genosystematics of Triaenophorus nodulosus (Cestoda: pseudophyllidea) from the Baikal lake

Data on a hook morphology (in plerocercoid and mature helminths) and gene systematics of Triaenophorus nodulosus from the Baikal Lake are presented for the first time. Sequence analysis of rDNA fragments (5'-end portion of 18S rDNA) yelded 562 nucleotid positions.     

Distribution and mechanism of the regulation of the pleurocercoid population count of Triaenophorus nodulosus (Cestoda, Triaenophoridae)

The character of the distribution of pleurocercoids of Triaenophorus nodulosus depending on the host age is shown. Their distribution in perch at the age of 0+-4+ is over dispersed in its character and is described by negative binomial. At the age of 5+ to 8+ the distribution of parasites is of regular character that is apparently due to changes in the mechanism of regulation of the parasites number. The regulation mechanism of the number of pleurocercoids of T. nodulosus is discussed.     

Ultrathin structure of the main lateral nerve cords and accompanying elements of Triaenophorus nodulosus (Cestoda: Pseudophyllidea)

The ultrastructure of lateral nerve cords (LNC) of Triaenophorus nodulosus has been studied. 4 of the 6 types of neurones earlier reported for cerebral ganglia are present in LNC: multipolars, bipolars, unipolars and "light"; neurosecretory cells of the 7th type lie in transverse commissures. The growth and formation of LNC occur at the expense of undifferentiated cells found on the cord periphery among mature neurones. LNC are surrounded with specialized envelopes made of cell processes of excretory vessels and a fibrillar matrix formed at early stages of cestode development. In large axons, cisternae of the cross reticulum are detected, which can serve as ultrastructural marker of the synapse. Two types of muscle innervation are determined. The direct innervation of muscular fibres is realized by peripheral neurosecretory neurones, which form contacts of the paracrine type. The central or sarco-neural innervation of muscular fibers occurs in LNC via the entering muscular processes.     

Mechanisms and specificity of amino acid transport in Taenia crassiceps larvae (Cestoda)

The absorption of lysine, arginine, phenylalanine and methionine by Taenia crassiceps larvae is linear with respect to time for at least 2 min. Arginine uptake occurs by a mediated system and diffusion, and arginine, lysine and ornithine (in order of decreasing affinity) are completely competitive inhibitors of arginine uptake. The basic amino acid transport system has a higher affinity for l-amino acids than d-amino acids, and blocking the α-amino group of an amino acid destroys its inhibitory action. Phenylalanine uptake by T. crassiceps larvae is inhibited in a completely competitive fashion by serine, leucine, alanine, methionine, histidine, phenylalanine, tyrosine and tryptophan (in order of increasing affinity). Methionine apparently binds non-productively to the phenylalanine (aromatic amino acid-preferring) transport system. l-methionine uptake by larvae is inhibited more by d-alanine and d-valine than by their respective l-isomers, while d- and l-methionine inhibit l-methionine uptake equally well. The presence of an unsubstituted α-amino group is essential for an inhibitor to have a high affinity for the methionine transport system. Uptake of arginine, phenylalanine and methionine is Na⁺-insensitive, and both phenylalanine and methionine are accumulated by larvae against a concentration difference in the presence or absence of Na⁺. Arginine accumulation is precluded by its rapid metabolism to proline, ornithine and an unidentified compound.     

Hymenolepis citelli (Cestoda) and Nematospiroides dubius (Nematoda): interspecific interaction in mice

In mice concurrently infected with Hymenolepis citelli and Nematospiroides dubius, survival of the tapeworm was prolonged, and there was an impairment of the efferent arm of the response to the cestode. The immunological rejection of a six cysticercoid primary H. citelli infection was delayed by the N. dubius infection. The growth of the cestode was poorer in concurrently infected mice, and this effect was rapid, being evident within 4 days of the N. dubius infection. Maximum biomass in the controls was reached on Day 20, whereas in the concurrently infected mice it was reached on Day 25. The induction of acquired immunity to homologous H. citelli infection was suppressed, although the expression of a secondary response against homologous challenge was not abrogated in doubly infected mice. The results are discussed with reference to the immunodepressive effects the nematode is known to have on heterologous antigenic stimulation.     

Subunit specificity and interaction domain between GABA(A) receptor-associated protein (GABARAP) and GABA(A) receptors

GABARAP (GABA(A) receptor-associated protein) interacts with both microtubules and GABA(A) receptors in vitro and in vivo and is capable of modulating receptor channel kinetics. In this study, we use the intracellular loop of 15 GABA(A) receptor subunits to show that the interaction between GABARAP and GABA(A) receptor is specific for the gamma subunits. Pharmacological characterization of proteins purified by GABARAP affinity column indicates that native GABA(A) receptors interact with GABARAP. Quantitative yeast two-hybrid assays were used to identify the interaction domain in the gamma2 subunit for GABARAP binding, and to identify the interaction domain in GABARAP for GABA(A) receptor binding. A peptide corresponding to the GABARAP interaction domain in the gamma2 subunit was used to inhibit the interaction between GABARAP and the gamma2 subunit. In addition, the ability of GABARAP to promote cluster formation of recombinant receptors expressed in QT-6 fibroblasts was inhibited by a membrane-permeable form of this peptide in a time-dependent manner. The establishment of a model for GABARAP-induced clustering of GABA(A) receptors in living cells and the identification of subunit specificity and interaction domains in the interaction between GABARAP and GABA(A) receptors is a step in dissecting the function of GABARAP in GABA(A) receptor clustering and/or targeting.     

Investigation of the specificity of the interaction between colicin E9 and its immunity protein by site-directed mutagenesis

Comparison of the amino acid sequences of the C-terminal domain of three DNAase type E colicins has identified six candidate specificity determinants for the interaction of these E colicins with their homologous immunity proteins. We have changed these candidate specificity determinants of colicin E9, using site-directed mutagenesis, to the corresponding amino-acids of colicin E8. A 'mutant' colicin E9, in which four of the six candidate specificity determinants have been changed, demonstrated colicin activity against Escherichia coli indicator strains which carried either the E8imm or the E9imm genes, indicative of a 'novel' E. colicin. After changing all six of the candidate specificity determinants, the resulting colicin E9 'mutant' exhibited a phenotype very similar to that of colicin E8.     

Physiological role of the interaction between CARMIL1 and capping protein

The regulation of free barbed ends is central to the control of dynamic actin assembly and actin-based motility in cells. Capping protein (CP) is known to regulate barbed ends and control actin assembly in cells. The CARMIL family of proteins can bind and inhibit CP in vitro, but the physiological significance of the interaction of CARMIL with CP in cells is poorly understood. Mammalian cells lacking CARMIL1 have defects in lamellipodia, macropinocytosis, cell migration, and Rac1 activation. Here we investigate the physiological significance of the CARMIL1–CP interaction, using a point mutant with a well-defined biochemical defect. We find that the CARMIL1–CP interaction is essential for the assembly of lamellipodia, the formation of ruffles, and the process of macropinocytosis. In contrast, the interaction of CARMIL1 with CP shows little to no importance for other functions of CARMIL1, including localization of CARMIL1 to the membrane, activation of Rac1, and cell migration. One implication is that lamellipodia are only marginally important for cell migration in a wound-healing model. The results also suggest that the ability of CARMIL1 to inhibit CP in cells may be regulated.     

Physiological prerequisites for successful interaction between child and computer

The following specific psychophysiological functions, important for computer work, were identified in children aged five to six years: the functional mobility of nervous processes; the accuracy of hand kinesthesia; the functional state of the accommodative system of the eye; mental capacity, volume and concentration; and short-term memory function. A considerable number of preschoolers (47%) proved to have an insufficient level of development of body functions, necessary for successful interaction with a computer.     

Substrate specificity overlap and interaction between adrenoleukodystrophy protein (ALDP/ABCD1) and adrenoleukodystrophy-related protein (ALDRP/ABCD2)

X-linked adrenoleukodystrophy (X-ALD) is a neurodegenerative disorder caused by mutations in the ABCD1 gene, which encodes a peroxisomal member of the ATP-binding cassette (ABC) transporter subfamily D called ALDP. ALDP is supposed to function as a homodimer allowing the entry of CoA-esters of very-long chain fatty acids (VLCFA) into the peroxisome, the unique site of their β-oxidation. ALDP deficiency can be corrected by overexpression of ALDRP, its closest homolog. However, the exact nature of the substrates transported by ALDRP and its relationships with ALDP still remain unclear. To gain insight into the function of ALDRP, we used cell models allowing the induction in a dose-dependent manner of a wild type or a mutated non-functional ALDRP-EGFP fusion protein. We explored the consequences of the changes of ALDRP expression levels on the fatty acid content (saturated, monounsaturated, and polyunsaturated fatty acids) in phospholipids as well as on the levels of β-oxidation of 3 suspected substrates: C26:0, C24:0, and C22:6n-3 (DHA). We found an inverse correlation between the fatty acid content of saturated (C26:0, C24:0) and monounsaturated (C26:1, C24:1) VLCFA and the expression level of ALDRP. Interestingly, we obtained a transdominant-negative effect of the inactive ALDRP-EGFP on ALDP function. This effect is due to a physical interaction between ALDRP and ALDP that we evidenced by proximity ligation assays and coimmunoprecipitation. Finally, the β-oxidation assays demonstrate a role of ALDRP in the metabolism of saturated VLCFA (redundant with that of ALDP) but also a specific involvement of ALDRP in the metabolism of DHA.     

The potency and specificity of the interaction between the IA3 inhibitor and its target aspartic proteinase from Saccharomyces cerevisiae

The yeast IA3 polypeptide consists of only 68 residues, and the free inhibitor has little intrinsic secondary structure. IA3 showed subnanomolar potency toward its target, proteinase A from Saccharomyces cerevisiae, and did not inhibit any of a large number of aspartic proteinases with similar sequences/structures from a wide variety of other species. Systematic truncation and mutagenesis of the IA3 polypeptide revealed that the inhibitory activity is located in the N-terminal half of the sequence. Crystal structures of different forms of IA3 complexed with proteinase A showed that residues in the N-terminal half of the IA3 sequence became ordered and formed an almost perfect alpha-helix in the active site of the enzyme. This potent, specific interaction was directed primarily by hydrophobic interactions made by three key features in the inhibitory sequence. Whereas IA3 was cut as a substrate by the nontarget aspartic proteinases, it was not cleaved by proteinase A. The random coil IA3 polypeptide escapes cleavage by being stabilized in a helical conformation upon interaction with the active site of proteinase A. This results, paradoxically, in potent selective inhibition of the target enzyme.     

Geography and host specificity: two forces behind the genetic structure of the freshwater fish parasite Ligula intestinalis (Cestoda: Diphyllobothriidae)

Parasite species with global distributions and complex life cycles offer a rare opportunity to study alternative mechanisms of speciation and evolution in a single model. Here, genealogy and genetic structure, with respect to geography and fish host preference, have been analyzed for Ligula intestinalis, a tapeworm affecting freshwater fish. The data analyzed consisted of 109 tapeworms sampled from 13 fish host species in 18 different localities on a macrogeographic scale. Two mitochondrial genes, cytochrome oxidase subunit I and cytochrome B, and the nuclear sequence of intergenic transcribed spacer 2 (ITS2) were used for the genetic reconstruction. Different evolutionary patterns were found at the local and at the global geographic scales. On a local scale, the flat genetic structure was mainly attributed to contiguous range expansion. Migrating birds are the most likely cause of the homogenisation of the whole population, preventing the creation of significant genetic barriers. By contrast, on a global scale, genetically distant and well-separated clusters are present in different geographic areas. Reproductive isolation was found even between clades living in sympatry and infecting the same definitive host, suggesting the existence of efficient biologically determined genetic barriers, and thus possibly separate species. Although the ITS2 sequences were found to display considerable intragenomic variability, their relationships were generally in good agreement with the topology derived from mitochondrial genes.