Ultrastructure of the surface of the osphradium of the anterior gilled mollusk Murex saxatilis L

The Murex saxatilis L. (Mollusca, Prosobranchia) osphradium is of the most complex "ctenidial" type and is situated immediately behind the siphon that brings water to the mantel cavity. By means of scanning and transmissive electron microscopical investigation, three zones have been revealed on the surface of the osphradium petals: secretory, intermediate and receptory. The secretory zone occupies the lateral part of the petal and is formed with 1-2 layers of cells. The intermediate zone, as a narrow stria, is situated between the secretory and the receptory zones. Here, together with the secretory cells, the ciliary cells are present. The receptory zone occupies nearly the whole surface of the petal. It is much thicker and is formed of pseudostratified epithelium where 5-7 raws of nuclei can be counted. Besides the cell types mentioned, there are defined bipolar receptory cells in it. The apical surface of the receptory cells has up to 200 cilia, and fine peripheral processes--1-2 cilia. Presence of the complex receptory zone makes it possible to suggest certain differentiation of the stimuli already at the peripheral level of the sensory system.     

Lysozyme of the mollusk Unio pictorum and the sensitivity of alkanotrophic rhodococci to its effect

A preparation of lysozyme from a freshwater bivalve, Unio pictorum, has been isolated by sorption to chitin, and its physicochemical properties have been studied. An assessment of the sensitivity of 48 strains of rhodococci, belonging to the species Rhodococcus rubber, R. luteus, and R. erythropolis (Specialized Collection of Alkanotrophic Microorganisms of the Institute of Ecology and Genetics of Microorganisms, Ural Division of the Russian Academy of Sciences), which were isolated from diverse natural waters, to lysozyme of the mollusk Unio pictorum demonstrated that the three species differ in their sensitivity to its effects. The high resistance of rhodococci to lysozyme is indicative of their considerable permanence in hydrobiocenoses (and, therefore, ability to maintain self-purification of microbiocenoses from hydrocarbons).     

On the structure of the pulmonate osphradium

Summary The cellular organisation of the osphradium of Planorbarius as revealed by the previously described light microscope studies is confirmed in the present study. A third epithelial cell type, the basal cell, is described. Perception is carried out by dendritic processes from osphradial sensory neurones, forming free nerve-endings in the sensory region of the osphradial epithelium. Ciliated cells and secretory cells of the osphradial epithelium are concerned with the transport of material in the osphradial canal. Many of the ultrastructural features of molluscan central ganglia are present in the osphradial ganglion, including inter-axonal chemical synapses. Neuromuscular junctions are present in the sheath surrounding the organ and these may be involved in a behavioural response of the organ. The need for further electrophysiological studies is emphasised.     

Drosophila MICAL regulates myofilament organization and synaptic structure

The overall size and structure of a synaptic terminal is an important determinant of its function. In a large-scale mutagenesis screen, designed to identify Drosophila mutants with abnormally structured neuromuscular junctions (NMJs), we discovered mutations in Drosophila mical, a conserved gene encoding a multi-domain protein with a N-terminal monooxygenase domain. In mical mutants, synaptic boutons do not sprout normally over the muscle surface and tend to form clusters along synaptic branches and at nerve entry sites. Consistent with high expression of MICAL in somatic muscles, immunohistochemical stainings reveal that the subcellular localization and architecture of contractile muscle filaments are dramatically disturbed in mical mutants. Instead of being integrated into a regular sarcomeric pattern, actin and myosin filaments are disorganized and accumulate beneath the plasmamembrane. Whereas contractile elements are strongly deranged, the proposed organizer of sarcomeric structure, D-Titin, is much less affected. Transgenic expression of interfering RNA molecules demonstrates that MICAL is required in muscles for the higher order arrangement of myofilaments. Ultrastructural analysis confirms that myosin-rich thick filaments enter submembranous regions and interfere with synaptic development, indicating that the disorganized myofilaments may cause the synaptic growth phenotype. As a model, we suggest that the filamentous network around synaptic boutons restrains the spreading of synaptic branches.     

Neurons and their synaptic organization in the visual cortex of the rat

Summary Cells in the visual cortex (area 17) of adult rats were impregnated by the rapid Golgi method and characterized by light microscopy. Selected cells were then sectioned for electron microscopy and their cytological characteristics and the pattern of synapses on their cell bodies and dendrites were studied Twelve classical pyramidal cells from layers II–VI, two pyramid-like cells from layer VI, two inverted pyramidal cells from layers V and VI, ten spine-free non-pyramidal cells from layers II–VI and two spinous non-pyramidal cells from layer IV were examined.The cytoplasmic features of the identified cells, where these could be discerned, corresponded to those previously reported for the different cell types in conventionally prepared tissue. Pyramidal Cells received exclusively type 2 synaptic contacts on their cell bodies, type 1 contacts on their dendritic spines and a mixture of synaptic types (type II predominating) on their shafts, where synaptic density was relatively low. This pattern of synaptic contacts was consistent for all portions of the dendritic tree; inverted pyramidal cells and pyramid-like cells showed the same synaptic organization as classical pyramids. The axon collaterals of pyramidal cells established type I contacts with dendritic spines (or, rarely, shafts) of unknown origin. Non-Pyramidal Cells received both type 1 and type 2 contacts (the former predominating) on their cell bodies and dendrites. The spinous variety also received type I contacts on their dendritic spines. Axon terminal of spine-free non-pyramidal cells established type II synaptic contacts with dendritic shafts of unknown origin. The similarity in synaptic organization between the spine-free and spinous non-pyramidal cells examined in this study suggest that the latter correspond to the sparsely spinous stellate cells rather than to the spinous stellate cells of cat and monkey visual cortex.We thank the Medical Research Council for financial support     

Protein organization of rat synaptic plasma membranes and synaptic vesicles: A one- and two-dimensional study

The protein organization of rat brain synaptic plasma membranes (SPM) and synaptic vesicles (SV) was investigated by surface iodination and one- and two-dimensional electrophoresis. Polypeptides of molecular weights (MWs, in Kilodaltons) 170 K, 135 K, 96-86 K, 68-64-61 K, 56 K, 52 K, 38 K, 35-33 K, and 18 K are predominantly or exclusively exposed on the extracellular side of synaptosomes. Several polypeptides of MW between 70 K and 40 K are exclusively exposed on the cytoplasmic side of SPM. The use of two-dimensional electrophoresis allowed to recognize that, for some classes of MW, there are polypeptides of nearly the same MW and different isoelectric points exposed on both sides of SPM. The synaptosomal membrane shows a predominance of acidic proteins on the extracellular side and more neutral and basic proteins on the cytoplasmic side. With respect to SPM, SV are particularly enriched with polypeptides of MW 71 K, 56 K, 39-38 K, 32 K, 16 K, and 15 K. One of them, a doublet of MW 39-38 K, is the most highly labeled species upon surface iodination and is similar, but not identical, with a doublet located on the cytoplasmic side of SPM.     

Comparative study of the genotoxic response of freshwater mussels Unio tumidus and Unio pictorum to environmental stress

Genotoxic response of freshwater mussels U. tumidus and U. pictorum to environmental stress was studied using comet assay on hemocytes and gill cells. The mussels were acclimated to controlled laboratory conditions for 10 days, and then exposed at 4 sites in the Sava and Danube rivers in the area of the city of Belgrade. Samples of each species were taken after 7, 14, and 30 days of exposure. The mussels sampled immediately after acclimation served as controls. Genotoxic response in both species was induced earlier at sites receiving untreated wastewaters from the city’s main collectors (7 days), than at the site receiving only domestic wastewaters from small settlements located upstream from the city (30 days). There was a correlation between the comet tail intensity values in tissues of exposed mussels and the concentrations of zinc, copper, iron, and arsenic at the exposure sites. The genotoxic responses in both tissues of U. pictorum and in hemocytes of U. tumidus were similar, while U. tumidus gill cells failed to exhibit significant genotoxic response at two sites. These findings, together with higher mortality of U. tumidus at the most polluted sites, promote U. pictorum as a model for genotoxicity monitoring in freshwater environments.     

Neuronal and synaptic organization of the outer plexiform layer of the pigeon retina

The organization of the outer plexiform layer (OPL) of the pigeon retina is described by electron microscopy and Golgi impregnation. Six types of photoreceptor, four types of horizontal cell, eight types of bipolar cell, and an interplexiform cell type were found by Golgi impregnation. The OPL was tri-stratified due to the endings of the photoreceptors at three different levels. This stratification was reflected in the laminar arrangement of the dendrites of the horizontal and bipolar cells. Electron microscopy showed that the synaptic endings of the photoreceptors made ribbon synapses, both triads and dyads, and basal junctions with the process of second-order neurons. Horizontal cells formed conventional chemical synapses, while horizontal cell axon terminals were extensively linked by gap junctions.     

Structure and molecular organization of the centromere-kinetochore complex

For over a century, the terms centromere and kinetochore have been used interchangeably to describe a complex locus on eukaryotic chromosomes that attaches chromosomes to spindle fibres and facilitates chromosome movement in mitosis and meiosis. This region has become the focus of research aimed at defining the mechanism of chromosome segregation. A variety of new molecular probes and vastly improved optical-imaging technology have provided much new information on the structure of this locus and raised new hopes that an understanding of its function may soon be at hand.     

Structure and organization of the bovine beta-globin genes

Genomic clones spanning the entire cow beta-globin gene locus have been isolated and characterized. These clones demonstrate that the linkage of embryonic-like (epsilon) genes and pseudogenes (psi) to the previously described fetal (gamma) and adult (beta) genes is as follows: 5'-epsilon 3-epsilon 4-psi 3-beta-epsilon 1-epsilon 2-psi 1- psi 2-gamma-3'. Present data indicate that, like that of the goat, the fetal and adult genes arose via block duplication of an ancestral four- gene set: epsilon-epsilon-psi-beta. This duplication event preceded the divergence of cows and goats, which occurred greater than or equal to 18-20 Myr ago. However, cows do not have the additional four-gene block containing a preadult/stress globin gene (beta C). Furthermore, the cow fetal cluster contains an extra beta-like pseudogene, which apparently arose by a small-scale duplication. The fixation of this duplication may indicate a possible evolutionary role for pseudogenes.      

Structure and organization of the C4 genes

This 200 000 Mr serum protein is coded for by at least two separate loci, C4A and C4B, which map in the HLA Class III region on chromosome 6 in man. Both loci are highly polymorphic with more than 30 alleles, including null alleles assigned to the two loci. The complete nucleotide sequence of a full length C4A cDNA clone and a substantial part of a C4b cDNA clone has shown class differences which can be used to synthesize nucleotide probes specific for C4A and C4B. Three C4 loci of approximately 16 kilobases each spaced by 10 kilobases have been identified in DNA from one individual and aligned 30 kilobases from the factor B gene by overlapping cloned genomic fragments from a cosmid library. Characterization of these genes by restriction mapping, nucleotide sequence analysis and hybridization with C4A and C4B specific synthetic oligonucleotides show that these genes are very similar.