Evidence for a highly differentiated sex chromosome heteromorphism in the salamander Necturus maculosus (Rafinesque)

The mitotic chromosomes of the neotenic (sensu Gould, 1977, and Alberch et al., 1979) salamander Necturus maculosus (Rafinesque) have been examined using a C-band technique to demonstrate the distribution of heterochromatin. The C-banded mitotic chromosomes provide evidence of a highly differentiated XY male/XX female sex chromosome heteromorphism, in which the X and Y chromosomes differ greatly in size and morphology, and in the amount and distribution of C-band heterochromatin. The X chromosome represents one of the largest biarmed chromosomes in the karyotype and is indistinguishable from similar sized autosomes on the basis of C-band heterochromatin. The Y chromosome, on the other hand, is diminutive, morphologically distinct from all other chromosomes of the karyotype, and is composed almost entirely of C-band heterochromatin. The discovery of an X/Y chromosome heteromorphism in this species is consistent with the observation by King (1912) of a heteromorphic spermatogenic bivalent. Karyological and phylogenetic implications are discussed.     

Cytogenetics of the chinese giant salamander,Andrias davidianus (Blanchard): the evolutionary significance of cryptobranchoid karyotypes

Cytogenetic aspects of the cryptobranchid salamander Andrias davidianus of western China have been studied, including chromosome number and morphology, C-band patterns, meiosis, and the chromosomal localization of ribosomal 5S RNA genes. Our data regarding chromosome number (2n=60) and general chromosome morphology largely confirm the results of Morescalchi et al. (1977). The karyotype consists of 16 pairs of macrochromosomes that decrease gradually in relative length to 14 pairs of microchromosomes. Telocentric chromosomes are a conspicuous feature of the karyotype, representing more than half the genome. Differential staining reveals that all of the chromosomes, except four pairs of microchromosomes, have C-band heterochromatin in their centromeric regions, the amount varying irrespective of chromosome size. Faint bands of interstitial and telomeric C-band heterochromatin are found in mitotic chromosomes but are not seen in meiotic preparations. In C-banded mitotic preparations from a female, one of the smallest macrochromosome pairs is heteromorphic in respect to C-band heterochromatin and centromere position. In situ hybridization of an iodinated 5S RNA probe to meiotic chromosome preparations reveals that this repeated gene is clustered near the telomeric region of chromosome 7, a medium size telocentric, a location corresponding to a band of heterochromatin. Studies of spermatocytes indicate that the process of meiosis in A. davidianus closely resembles that of more advanced salamanders, and that the microchromosomes are meiotically stable. The significance of microchromosomes and chromosome morphology in the reorganization of salamander genomes during evolution is discussed on the basis of cytogenetic data available for A. davidianus and various other primitive and advanced salamanders.     

Modeling of substrate and inhibitor binding to phospholipase A2.

Molecular graphics and molecular mechanics techniques have been used to study the mode of ligand binding and mechanism of action of the enzyme phospholipase A2. A substrate-enzyme complex was constructed based on the crystal structure of the apoenzyme. The complex was minimized to relieve initial strain, and the structural and energetic features of the resultant complex analyzed in detail, at the molecular and residue level. The minimized complex was then used as a basis for examining the action of the enzyme on modified substrates, binding of inhibitors to the enzyme, and possible reaction intermediate complexes. The model is compatible with the suggested mechanism of hydrolysis and with experimental data about stereoselectivity, efficiency of hydrolysis of modified substrates, and inhibitor potency. In conclusion, the model can be used as a tool in evaluating new ligands as possible substrates and in the rational design of inhibitors, for the therapeutic treatment of diseases such as rheumatoid arthritis, atherosclerosis, and asthma.     

A correlation between BCL-2 modifying factor,p53 and livin gene expressions in cancer colon patients

Accumulating evidence has revealed that livin gene and BCL-2 modifying factor (BMF) gene are closely associated with the initiation and progression of colon carcinoma by activating or suppressing multiple malignant processes. Those genes that can detect colon - cancer are a promising approach for cancer screening and diagnosis. This study aimed to evaluate correlation between livin, BMF and p53 genes expression in colon cancer tissues of patients included in the study, and their relationship with clinicopathological features and survival outcome in those patients. In this study, 50 pathologically diagnosed early cancer colon patients included and their tissue biopsy with 50 matched adjacent normal tissue, and 50 adenoma tissue specimens were analyzed for livin gene and BMF gene expressions using real time PCR. The relationship of those genes expressions with clinicopathological features, tumor markers, Time to Progression and overall survival for those patients were correlated in cancer colon group. In this study, there was a significant a reciprocal relationship between over expression of livin gene and down regulation of BMF and p53 genes in colon cancer cells. Livin mRNA was significantly higher, while BMF and p53 mRNA were significantly lower in colorectal cancer tissue compared to benign and normal colon tissue specimens (P < 0.001), however, this finding was absent between colon adenomas and normal mucosa. There was a significant association between up regulation of livin and down regulation of BMF and p53 expressions with more aggressive tumor (advanced TNM stage), rapid progression with metastasis and decreased overall survival in cancer colon patients, hence these genes can serve as significant prognostic markers of poor outcome in colon cancer patients. This work highlights the role of livin, BMF and p53 genes in colorectal tumorigenesis and the applicability of using those genes as a diagnostic and prognostic markers in patients with colon carcinoma and as a good target for cancer colon treatment in the future.     

Biocides formulation of essential oils having antimicrobial activity

Essential oils of fennel, peppermint, caraway, eucalyptus, geranium and lemon were tested for their antimicrobial activities against some plant pathogenic micro-organisms (Fusarium oxysporum, Alternaria alternate, Penicilium italicum Penicilium digitatum and Botyritus cinerea). Essential oils of fennel, peppermint, caraway were selected as an active ingredient for the formulation of biocides due to their efficiency in controlling the tested micro-organisms. Successful emulsifiable concentrates (biocides) were prepared from these oils using different emulsifiers (Emulgator B.L.M. Tween20 and Tween80) and different fixed oils (sesame, olive, cotton and soybean oils). Physico-chemical properties of the formulated biocide (spontaneous emulsification, emulsion stability test, cold stability and heat stability tests as well as viscosity, surface tension and pH) were measured. The prepared biocides were ready to be tested for application in a future work as a safe pesticide against different pathogens.     

The role of charged residues in the transmembrane helices of monocarboxylate transporter 1 and its ancillary protein basigin in determining plasma membrane expression and catalytic activity

Monocarboxylate transporters MCT1-MCT4 require basigin (CD147) or embigin (gp70), ancillary proteins with a glutamate residue in their single transmembrane (TM) domain, for plasma membrane (PM) expression and activity. Here we use site-directed mutagenesis and expression in COS cells or Xenopus oocytes to investigate whether this glutamate (Glu₂₁₈ in basigin) may charge-pair with a positively charged TM-residue of MCT1. Such residues were predicted using a new molecular model of MCT1 based upon the published structure of the E. coli glycerol-3-phosphate transporter. No evidence was obtained for Arg₃₀₆ (TM 8) of MCT1 and Glu₂₁₈ of basigin forming a charge-pair; indeed E218Q-basigin could replace WT-basigin, although E218R-basigin was inactive. No PM expression of R306E-MCT1 or D302R-MCT1 was observed but D302R/R306D-MCT1 reached the PM, as did R306K-MCT1. However, both were catalytically inactive suggesting that Arg₃₀₆ and Asp₃₀₂ form a charge-pair in either orientation, but their precise geometry is essential for catalytic activity. Mutation of Arg₈₆ to Glu or Gln within TM3 of MCT1 had no effect on plasma membrane expression or activity of MCT1. However, unlike WT-MCT1, these mutants enabled expression of E218R-basigin at the plasma membrane of COS cells. We propose that TM3 of MCT1 lies alongside the TM of basigin with Arg₈₆ adjacent to Glu₂₁₈ of basigin. Only when both these residues are positively charged (E218R-basigin with WT-MCT1) is this interaction prevented; all other residue pairings at these positions may be accommodated by charge-pairing or stabilization of unionized residues through hydrogen bonding or local distortion of the helical structure.     

Metagenomic insights into strategies of carbon conservation and unusual sulfur biogeochemistry in a hypersaline Antarctic lake

Organic Lake is a shallow, marine-derived hypersaline lake in the Vestfold Hills, Antarctica that has the highest reported concentration of dimethylsulfide (DMS) in a natural body of water. To determine the composition and functional potential of the microbial community and learn about the unusual sulfur chemistry in Organic Lake, shotgun metagenomics was performed on size-fractionated samples collected along a depth profile. Eucaryal phytoflagellates were the main photosynthetic organisms. Bacteria were dominated by the globally distributed heterotrophic taxa Marinobacter, Roseovarius and Psychroflexus. The dominance of heterotrophic degradation, coupled with low fixation potential, indicates possible net carbon loss. However, abundant marker genes for aerobic anoxygenic phototrophy, sulfur oxidation, rhodopsins and CO oxidation were also linked to the dominant heterotrophic bacteria, and indicate the use of photo- and lithoheterotrophy as mechanisms for conserving organic carbon. Similarly, a high genetic potential for the recycling of nitrogen compounds likely functions to retain fixed nitrogen in the lake. Dimethylsulfoniopropionate (DMSP) lyase genes were abundant, indicating that DMSP is a significant carbon and energy source. Unlike marine environments, DMSP demethylases were less abundant, indicating that DMSP cleavage is the likely source of high DMS concentration. DMSP cleavage, carbon mixotrophy (photoheterotrophy and lithoheterotrophy) and nitrogen remineralization by dominant Organic Lake bacteria are potentially important adaptations to nutrient constraints. In particular, carbon mixotrophy relieves the extent of carbon oxidation for energy production, allowing more carbon to be used for biosynthetic processes. The study sheds light on how the microbial community has adapted to this unique Antarctic lake environment.     

Enzymatic properties of the lactate dehydrogenase enzyme from Plasmodium falciparum

The lactate dehydrogenase enzyme from Plasmodium falciparum (PfLDH) is a target for antimalarial compounds owing to structural and functional differences from the human isozymes. The plasmodial enzyme possesses a five-residue insertion in the substrate-specificity loop and exhibits less marked substrate inhibition than its mammalian counterparts. Here we provide a comprehensive kinetic analysis of the enzyme by steady-state and transient kinetic methods. The mechanism deduced by product inhibition studies proves that PfLDH shares a common mechanism with the human LDHs, that of an ordered sequential bireactant system with coenzyme binding first. Transient kinetic analysis reveals that the major rate-limiting step is the closure of the substrate-specificity loop prior to hydride transfer, in line with other LDHs. The five-residue insertion in this loop markedly increases substrate specificity compared with the human muscle and heart isoforms.