Changes in the antigenic phenotype of mouse thymocytes after exposure to chemical inducers of differentiation and ionizing radiation

Irradiation of a mouse thymocyte fraction enriched by T-lymphocyte precursors changes the antigenic phenotype of cells toward the increase of their highly differentiated forms. Similar changes in membrane marker antigens are produced by chemical inductors of differentiation and thymotropin. The changes in the cell phenotype induced by the above agents are associated with both membrane and intragenome rearrangements. The results of the experiments on preventing the expression of some antigens by puromycin and the data on the level of spontaneous genome lesions in thymocyte fractions have prompted an assumption that destabilization of the genome upon irradiation increases DNA injury above some critical level which may serve a stimulus for "sorting out" the most radiosensitive thymocyte fraction.     

Sequence divergence of the mitochondrial DNA of Pacific Ocean salmon

Restriction assay of mtDNA has been made in 6 salmon species form the genus Oncorhynchus and one species from the related genus, i.e. Salvelinus malma. The size of the mitochondrial genome was found to be identical and equal to 16.7 kilobases. The digestion patterns of mtDNA cleaved by 5 restriction endonucleases (Eco RI, Bgl I, Bgl II, Hind III, and Pst I) were used for analysis of the levels of interspecific variation and for estimation the matrix of mtDNA sequence differentiation. It was found that the level of nucleotide sequence divergence (p) in the genus Oncorhynchus varies within 1.7-6.7%. Minimum p value was observed in a pair O. keta--O. gorbuscha, maximum one--between O. masu and other species. With respect to similarity in their mtDNA, three groups may be distinguished: 1) O. gorbuscha--O. keta; 2) O. nerka--O. kisutch, O. tschawytscha; 3) O. masu. Mean value of intergeneric level of sequence divergence between Oncorhynchus and Salvelinus was found to be equal to 8%. On the basis of mtDNA analysis, the dendrogram of similarity of the species was plotted which is consistent in principle with current viewpoints on phylogenetic relations among the Pacific salmon.     

Localization of the multigene Lpm locus in chromosome 9 of the American mink

The results of genetic study on linkage of Lpm locus with peptidase B gene are presented. Investigation of 111 offspring back-crosses shows that Lpm allotypes and allelic variants of peptidase B are inherited in concert. The frequency of recombination between the Lpm locus and peptidase B gene is 11 +/- 3% in male. Since it was earlier established that peptidase B gene is a marker of chromosome 9, our data indicate that the Lpm loci family is situated in the chromosome 9 of domestic mink.     

Regular proteinaceous layers ofThermococcus stetteri cell envelope

Proteinaceous layers of theThermococcus stetteri cell envelope were investigated and found to consist of regularly arrayed subunits 18 nm in diameter. According to the results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, two major proteins were present. They were glycosylated and had molecular weights of 80,000 and 210,000. In addition to two external regular proteinaceous layers, cells ofT. stetteri were found to have internal regular layers tightly attached to the cytoplasmic membrane. In the region of flagella attachment to the cell, polar membrane-like structures were found in the cytoplasm.     

Tooth replacement rates in early chondrichthyans: a qualitative approach

The continuous replacement of teeth throughout their lifetime is a common characteristic of most chondrichthyans. This process was already present in the earliest representatives of the group. It has been well established that different species of extant sharks show rapid tooth replacement rates; however, some authors have suggested that in early chondrichthyans this rate might have been much slower. Here we present a qualitative approach to analyse tooth replacement rates in the Early Devonian shark Leonodus carlsi , the earliest tooth-bearing shark known to date. For this, we have examined 1,103 isolated teeth from Celtiberia, Spain. Our study provides strong evidences of an extremely slow dental replacement in this primitive chondrichthyan based on three independents analyses: (1) statistical analysis of the wear degree, demonstrating that teeth remain functional for a long period of time; (2) analysis of both the histological and the morphological features of the teeth cusps suggests that this chondrichthyan used a maturation process that optimizes its function, thus worn teeth show an efficient working shape that implies their teeth remained functional for a long time after being modelled by use; and (3) estimations of size increments between teeth (Δs) of the same dental family for some recent sharks whose rates of replacement were known prove that Δs is inversely proportional to the rate of replacement ( R ² = 0.8327). The estimated values of tooth replacement rates obtained from Δs for L. carlsi and for some Late Devonian cladoselachian sharks are significatively slower than those observed in current sharks.     

Ligands of boron in Pisum sativum nodules are involved in regulation of oxygen concentration and rhizobial infection

Boron (B) is an essential nutrient for N₂‐fixing legume–rhizobia symbioses, and the capacity of borate ions to bind and stabilize biomolecules is the basis of any B function. We used a borate‐binding‐specific resin and immunostaining techniques to identify B ligands important for the development of Pisum sativum–Rhizobium leguminosarum 3841 symbiotic nodules. arabinogalactan–extensin (AGPE), recognized by MAC 265 antibody, appeared heavily bound to the resin in extracts derived from B‐sufficient, but not from B‐deficient nodules. MAC 265 stained the infection threads and the extracellular matrix of cortical cells involved in the oxygen diffusion barrier. In B‐deprived nodules, immunolocalization of MAC 265 antigens was significantly reduced. Leghaemoglobin (Lb) concentration largely decreased in B‐deficient nodules. The absence of MAC 203 antigens in B‐deficient nodules suggests a high internal oxygen concentration, as this antibody detects an epitope on the lipopolysaccharide (LPS) of bacteroids typically expressed in micro‐aerobically grown R. leguminosarum 3841. However, B‐deprived nodules did not accumulate oxidized lipids and proteins, and revealed a decrease in the activity of the major antioxidant enzyme ascorbate peroxidase (APX). Therefore, B deficiency reduced the stability of nodule macromolecules important for rhizobial infection, and for regulation of oxygen concentration, resulting in non‐functional nodules, but did not appear to induce oxidative damage in low‐B nodules.     

Long-term exposure of Boeckellagibbosa (Copepoda, Calanoida) to in situ levels of solar UVB radiation

1. The freshwater calanoid copepod Boeckella gibbosa is typical of high elevation lakes and ponds in Patagonia (Argentina). Previous studies have shown that this species is highly tolerant to short-term exposure to natural and artificial UVB radiation, and that its tolerance is due to photoreactivation by longer wavelength radiation. In this study, we investigate the potential sublethal effects of solar radiation after prolonged exposure.
2. We incubated B. gibbosa at 1 m depth in oligotrophic Lake Toncek for 24 days. The incubation chambers were 1.2 l acrylic cylinders covered with appropriate filters in order to obtain three radiation treatments: visible radiation only, visible radiation + UVA and visible radiation + UVA + UVB.
3. The three treatments did not differ significantly in variables considered as indicators of survival (number of individuals), reproduction (proportion of ovigerous females, clutch size) and development (instar composition). Although resistance to solar UVB radiation is certainly a requisite to live in transparent high elevation habitats, the fact of being effectively exposed to natural levels of UVB radiation does not seem to have measurable consequences on an already adapted species, such as B. gibbosa     

Phylogeography of mitochondrial DNA in South Asian Dolly Varden char Salvelinus curilus Pallas, 1814 (Salmoniformes, Salmonidae): mediated gene introgression?

In 41 individuals of South Asian Dolly Varden char Salvelinus curilus, nucleotide sequences of tRNA-Pro gene fragment (27 bp) and mtDNA control region (483-484 bp) were analyzed. The fish were collected in 20 localities covering virtually the whole range of the species: Kuril Islands, Sakhalin Island. and Primorye. In addition, six individuals of three other char species (S. albus, S. malma, and S. leucomaenis), which are closely related to S. curilus and inhabit the Russian Far East, were examined. In all, we detected 12 different variants of mtDNA haplotypes that formed three distinct groups differing in 14--20 nucleotide positions. The first group consisted of six haplotypes found in S. curilus in Kuril Islands, Sakhalin, and Primorye (mtDNA phylogroup OKHOTSKIA). The second group comprised four haplotypes representing the mtDNA phylogroup BERING, which had been described earlier (Brunner et al, 2001); they were found in S. curilus in Kuril Islands and Sakhalin, as well as in S. albus and S. malma in Kamchatka and northern Kurils. The third group included two haplotypes detected in S. leucomaenis. The existence of two mtDNA lineages (OKHOTSKIA and BERING) in S. curilus from Kurils and Sakhalin was explained by hybridization and DNA transfer from S. malma to S. curilus. The absence of the BERING haplotypes in S. curilus from Primorye water reservoirs is related to the physical isolation of the Sea of Okhotsk and Sea of Japan basins in past epochs. On the basis of comparing phylogenetic trees, constructed from the data on allozyme and mtDNA variation, we suggest that in this case, an indirect transfer of mtDNA in Alpinoid chars--> S. malma-->S. curilus chain could occur.     

Impedance Matching Induce High Transmission and Flat Response Band-Pass Plasmonic Waveguides

We consider a model utilizing the concept of impedance matching, which can be applied to design the coupled cascaded plasmonic cavity waveguide with desired properties. We use a transfer matrix method to obtain its transmission and dispersion diagrams. Base on this method, we demonstrate that a band-pass metal–dielectric–metal plasmonic filter with quasi-flat group velocity and tunable bandwidth can be achieved.     

Divergence patterns of banding sequences in different polytene chromosome arms reflect relatively independent evolution of different genome components

Divergence patterns of the banding sequences from the chromosomal arms A, C, D, E, and F were compared in 63 species of the genus Chironomus. Evaluation of the number of breakpoints between the pairs of inverted banding sequences and the analysis of the lengths of the conserved segments in the chromosomal arms in the chironomid species examined showed that different arms evolved relatively independently and at different rates. No direct correlation between the arm length and the breakpoints number was observed. The length of the conservative segment was not fixed, but was arm-specific. Robustness and fidelity of the estimates of phylogenetic relationships between the species examined increased with the arm number, i.e., with the genome proportion included in the analysis.