Topoisomerases of kinetoplastid parasites as potential chemotherapeutic targets

The protozoan parasites Trypanosoma, Leishmania and Crithidia, which belong to the order kinetoplastidae, emerge from the most ancient eukaryotic lineages. The diversity found in the life cycle of these organisms must be directed by genetic events, wherein topoisomerases play an important role in cellular processes affecting the topology and organization of intracellular DNA. Topoisomerases are valuable as potential drug targets because they have indispensable function in cell biology. This review summarizes what is known about topoisomerase genes and proteins of kinetoplastid parasites and the roles of these enzymes as targets for therapeutic agents.     

Intergenerational trend of some dermatoglyphic traits in Vaidyas of West Bengal, India

In order to investigate the intergenerational change of dermatoglyphics, fingerprints of 400 individuals were collected from an endogamous caste Vaidyas of Barasat, West Bengal. Results were compared with the data of an earlier sample of Banerjee collected in 35 years before on the same community of the same area. As it is generally known that dermatoglyphics is selectively neutral, thus if no other evolutionary forces play a role, we cannot expect any change of dermatoglyphic characters after several years. In the present study, non-significant change in the frequency of pattern and more or less same PII have been observed in both sexes. But significant quantitative differences were found between the two samples. These differences may not be due to the change of intra-uterine environment, rather due to the inter-observer error of these two studies and the small sample size of the earlier study. Because though same methods were used in both studies, inter-observer variation is much possible in ridge counting than pattern type determination.     

The amyloid beta peptide (Abeta(1-40)) is thermodynamically soluble at physiological concentrations

Precipitation of the 39-43-residue amyloid beta peptide (Abeta) is a crucial factor in Alzheimer's disease (AD). In normal as well as in AD-afflicted brain, the Abeta concentration is estimated to be a few nanomolar. Here we show that Abeta(1-40) precipitates in vitro only if the dissolved concentration is >14 microM. Using fluorescence correlation spectroscopy, we further show that the precipitation is complete in 1 day, after which the size distribution of Abeta monomer/oligomers in the solution phase becomes stationary in time and independent of the starting Abeta concentration. Mass spectra confirm that both the solution phase and the coexisting precipitate contain chemically identical Abeta molecules. Incubation at 68 degrees C for 1 h reduces the solubility by <12%. Together, these results show that the thermodynamic saturation concentration (C(sat)) of Abeta(1-40) in phosphate-buffered saline (PBS) at pH 7.4 has a well-defined lower limit of 15.5 +/- 1 microM. Divalent metal ions (believed to play a role in AD) at near-saturation concentrations in PBS reduce C(sat) only marginally (2 mM Mg(2+) by 6%, 2.5 microM Ca(2+) by 7%, and 4 microM Zn(2+) by 11%). Given that no precipitation is possible at concentrations below C(sat), we infer that coprecipitant(s), and not properties of Abeta(1-40) alone, are key factors in the in vivo aggregation of Abeta.     

Specification of thermosensory neuron fate in C. elegans requires ttx-1, a homolog of otd/Otx

Temperature is a critical modulator of animal metabolism and behavior, yet the mechanisms underlying the development and function of thermosensory neurons are poorly understood. C. elegans senses temperature using the AFD thermosensory neurons. Mutations in the gene ttx-1 affect AFD neuron function. Here, we show that ttx-1 regulates all differentiated characteristics of the AFD neurons. ttx-1 mutants are defective in a thermotactic behavior and exhibit deregulated thermosensory inputs into a neuroendocrine signaling pathway. ttx-1 encodes a member of the conserved OTD/OTX homeodomain protein family and is expressed in the AFD neurons. Misexpression of ttx-1 converts other sensory neurons to an AFD-like fate. Our results extend a previously noted conservation of developmental mechanisms between the thermosensory circuit in C. elegans and the vertebrate photosensory circuit, suggesting an evolutionary link between thermosensation and phototransduction.     

Induction of blindness by formoguanamine hydrochloride in adult male roseringed parakeets (Psittacula krameri)

Formoguanamine (2,4-diamino-s-triazine) was known to be an effective chemical agent in inducing blindness in poultry chicks, but not in adult birds. The present study was undertaken to demonstrate the influences, if any, of this chemical on the visual performance and retinal histology in an adult sub-tropical wild bird, the roseringed parakeet (Psittacula krameri). Formoguanamine (FG) hydrochloride was subcutaneously injected into adult parakeets at a dosage of 25 mg (dissolved in 0.75 ml physiological saline)/100 g body weight/day, for two consecutive days while the control birds were injected only with a placebo. The effects were studied after 10, 20 and 30 days of the last treatment of FG. Within 24 h of the treatment of FG, about 90% of the total birds exhibited lack of visual responses to any light stimulus and even absence of pupillary light reactions. The remaining birds became totally blind on the day following the last injection of FG and remained so till the end of investigation. At the microscopic level, conspicuous degenerative changes were noted in the outer pigmented epithelium and the photoreceptive layer of rods and cones in the retinas of FG treated birds. A significant reduction in the thickness of the outer nuclear layer was also found in the retinas of FG treated parakeets, compared to that in the control birds. However, the inner cell layers of the retina in the control and FG administered parakeets were almost identical. It deserves special mention that the effects of FG, noted after 30 days of last treatment, were not very different from those noted just after 10 days of treatment. Collectively, the results of the present investigation demonstrate that FG can be used as a potent pharmacological agent for inducing irreversible blindness through selective damage in retinal tissue even in the adult wild bird, thereby making FG treatment an alternative euthanasic device to a cumbersome, stressful, surgical method of enucleation of the ocular system for laboratory studies.     

The p53 tumour suppressor inhibits glucocorticoid-induced proliferation of erythroid progenitors

Hypoxia encountered at high altitude, blood loss and erythroleukemia instigate stress erythropoiesis, which involves glucocorticoid-induced proliferation of erythroid progenitors (ebls). The tumour suppressor p53 stimulates hematopoietic cell maturation and antagonizes glucocorticoid receptor (GR) activity in hypoxia, suggesting that it may inhibit stress erythropoiesis. We report that mouse fetal liver ebls that lack p53 proliferate better than wild-type cells in the presence of the GR agonist dexamethasone. An important mediator of GR-induced ebl self-renewal, the c-myb gene, is induced to higher levels in p53^–/– ebls by dexamethasone. The stress response to anemia is faster in the spleens of p53^–/– mice, as shown by the higher levels of colony forming units erythroids and the increase in the CD34/c-kit double positive population. Our results show that p53 antagonizes GR-mediated ebl expansion and demonstrate for the first time that p53–GR cross-talk is important in a physiological process in vivo: stress erythropoiesis.     

Locking and unlocking of ribosomal motions

During the ribosomal translocation, the binding of elongation factor G (EF-G) to the pretranslocational ribosome leads to a ratchet-like rotation of the 30S subunit relative to the 50S subunit in the direction of the mRNA movement. By means of cryo-electron microscopy we observe that this rotation is accompanied by a 20 A movement of the L1 stalk of the 50S subunit, implying that this region is involved in the translocation of deacylated tRNAs from the P to the E site. These ribosomal motions can occur only when the P-site tRNA is deacylated. Prior to peptidyl-transfer to the A-site tRNA or peptide removal, the presence of the charged P-site tRNA locks the ribosome and prohibits both of these motions.     

Immunohistochemical localization of leukemia inhibitory factor, interleukins 1 and 6 at the primary implantation site in the rhesus monkey

Blastocyst implantation and placentation involve localized inflammatory type of responses at and around the site of nidation. In the present study, the likely involvement of inflammatory cytokines, namely, leukemia inhibitory factor (LIF), interleukins 1 alpha and 1 beta (IL-1alpha and IL-1beta) and IL-6 at the primary implantation site of the rhesus monkey was examined immunocytochemically during lacunar (n=6) and villous (n=8) stages of gestation. Trophoblast cells and extraembryonic mesenchymal cells were immunopositive for LIF and IL-1alpha. The distribution of IL-1beta and IL-6 in trophoblast cells was low in lacunar stage samples, however, a higher degree of immunopositivity for IL-6 was observed in villous stage samples. Decidual cells were immunopositive for all the cytokines studied. In lacunar stage samples, plaque cells adjacent to implanted nidus were immunopositive for all the cytokines examined, and the degree of their immunoprecipitation increased, except that of IL-1beta, during the villous stage. Luminal and glandular epithelial cells were immunopositive for LIF, IL-1alpha, IL-1beta and IL-6 in lacunar and in villous stage samples. LIF immunopositivity was detected in endothelial cells of blood vessels within and below chorionic plate and cytotrophoblast shell, while vascular smooth muscle cells were positive for all the cytokines studied. The temporo-spatial characteristics of LIF, IL-1alpha, IL-1beta and IL-6 protein expressions in primary implantation sites of the rhesus monkey suggest that these pro-inflammatory cytokines play specific roles in regulating trophoblast cell proliferation, differentiation, invasion and associated maternal tissue remodelling during early gestation.     

Incorporation of aminoacyl-tRNA into the ribosome as seen by cryo-electron microscopy

Aminoacyl-tRNAs (aa-tRNAs) are delivered to the ribosome as part of the ternary complex of aa-tRNA, elongation factor Tu (EF-Tu) and GTP. Here, we present a cryo-electron microscopy (cryo-EM) study, at a resolution of approximately 9 A, showing that during the incorporation of the aa-tRNA into the 70S ribosome of Escherichia coli, the flexibility of aa-tRNA allows the initial codon recognition and its accommodation into the ribosomal A site. In addition, a conformational change observed in the GTPase-associated center (GAC) of the ribosomal 50S subunit may provide the mechanism by which the ribosome promotes a relative movement of the aa-tRNA with respect to EF-Tu. This relative rearrangement seems to facilitate codon recognition by the incoming aa-tRNA, and to provide the codon-anticodon recognition-dependent signal for the GTPase activity of EF-Tu. From these new findings we propose a mechanism that can explain the sequence of events during the decoding of mRNA on the ribosome.