Evidences for genetic differentiation within the highly endemic and endangered annual fish Austrolebias nigrofasciatus (Cyprinodontiformes: Rivulidae)

Samples of Austrolebias nigrofasciatus (n = 103), an endangered species of annual fish endemic to a small area of the Patos-Mirim lagoon system encompassing the São Gonçalo Channel lowlands, were collected from eight isolated temporary ponds, four located at the known distribution range of the species and four located along the Piratini River lowlands, where morphologically different individuals were found. In the laboratory, fragments of the mitochondrial cytochrome c oxidase I (coI), cytochrome b (cytb) and nuclear rhodopsin (rho) genes were amplified, purified and sequenced for 100, 99 and 58 of these individuals, respectively. Samples were further analysed using phylogenetic and phylogeographic methods to evaluate the patterns of genetic diversity and differentiation presented within and between populations, while assessing their evolutionary history, in order to guide the application of further conservation strategies. We found that the four new populations from the Piratini River lowlands encompass a different lineage of A. nigrofasciatus that diverged from that encountered in the São Gonçalo Channel at approximately 0.165 M years before present, during a population expansion and did not yet attain reciprocal monophyly. This divergence was associated with a glacial event that was preceded by an interglacial period putatively associated with the dispersal. Moreover, significant levels of genetic differentiation and a high number of exclusive haplotypes could be encountered even in micro-geographical scales, as in the comparisons between populations located within the same major lineage, indicating each of them may encompass independent management units. Conservation actions are certainly urgent, especially in the face of signs of a recent bottleneck.     

Active site mutations in DNA topoisomerase I distinguish the cytotoxic activities of camptothecin and the indolocarbazole, rebeccamycin.

DNA topoisomerase I (Top1p) catalyzes topological changes in DNA and is the cellular target of the antitumor agent camptothecin (CPT). Non-CPT drugs that target Top1p, such as indolocarbazoles, are under clinical development. However, whether the cytotoxicity of indolocarbazoles derives from Top1p poisoning remains unclear. To further investigate indolocarbazole mechanism, rebeccamycin R-3 activity was examined in vitro and in yeast. Using a series of Top1p mutants, where substitution of residues around the active site tyrosine has well-defined effects on enzyme catalysis, we show that catalytically active, CPT-resistant enzymes remain sensitive to R-3. This indolocarbazole did not inhibit yeast Top1p activity, yet was effective in stabilizing Top1p-DNA complexes. Similar results were obtained with human Top1p, when Ser or His were substituted for Asn-722. The mutations altered enzyme function and sensitivity to CPT, yet R-3 poisoning of Top1p was unaffected. Moreover, top1delta, rad52delta yeast cells expressing human Top1p, but not catalytically inactive Top1Y723Fp, were sensitive to R-3. These data support hTop1p as the cellular target of R-3 and indicate that distinct drug-enzyme interactions at the active site are required for efficient poisoning by R-3 or CPT. Furthermore, resistance to one poison may potentiate cell sensitivity to structurally distinct compounds that also target Top1p.     

Genotoxicity studies with four organophosphorus insecticides using the unstable white-zeste system of Drosophila melanogaster

The present study was carried out to evaluate the suitability of the unstable white-zeste system in Drosophila melanogaster by testing 4 organophosphorus insecticides for potential genotoxic activity: dimethoate, fenitrothion, malathion, and methyl parathion. In view of the high sensitivity to insecticides of the unstable zeste strain used in this assay and the negative results obtained in this work, the white-zeste system does not appear to be sufficiently accurate for the evaluation of the mutagenic potential of specifically toxic chemicals, like insecticides.     

Testing of chloroquine and quinacrine for mutagenicity in Drosophila melanogaster

To extend the data on the mutagenic effects of intercalating agents in Drosophila melanogaster, chloroquine and quinacrine were tested for the induction of genetic damage in D. melanogaster males. Sex-linked recessive lethals and sex-chromosome loss induction were studied following treatment of adult males using a feeding technique. Our results show that both intercalating compounds increase significantly the frequency of sex-linked recessive lethals, but are unable to induce sex-chromosome loss in male germ cells under the conditions of testing.     

Volume density of syncytial sprouts and its regional variation in the human mature placenta

The authors studied by means of sterological methods the volume density of syncytial sprouts in different cotyledonary regions of the human term placenta. The syncytial sprouts account for 4.92% of the placenta volume. Meanwhile, there were significant differences according to the site from which the sample was obtained. The lowest value (2.72%) corresponds to the central-parabasal zone of the cotyledon, close to the entry of the maternal blood into the intervillous space, whereas the highest values correspond to the "venous" regions. The results of the present study, as well as those reported by others, suggest that the lateral-subchorial zone would be the growing region of the cotyledon.     

Molecular control mechanisms of lysine and threonine biosynthesis in amino acid-producing corynebacteria: Redirecting carbon flow

Abstract Threonine and lysine are two of the economically most important essential amino acids. They are produced industrially by species of the genera Corynebacterium and Brevibacterium . The branched biosynthetic pathway of these amino acids in corynebacteria is unusual in gene organization and in the control of key enzymatic steps with respect to other microorganisms. This article reviews the molecular control mechanisms of the biosynthetic pathways leading to threonine and lysine in corynebacteria, and their implications in the production of these amino acids. Carbon flux can be redirected at branch points by gene disruption of the competing pathways for lysine or threonine. Removal of bottlenecks has been achieved by amplification of genes which encode feedback resistant aspartokinase and homoserine dehydrogenase (obtained by in vitro directed mutagenesis).     

Complete sequence of a new HLA-B35 allele found in a tribe of Mapuche Indians in the south of Argentina

The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession number U17107. The nameB*3509 was officially assigned by the WHO Nomenclature Committee in December 1994     

Alpha-neo-endorphin-like immunoreactivity in the cat brain stem

This paper examines the distribution of fibers and cell bodies containing alpha-neo-endorphin in the cat brain stem by using an indirect immunoperoxidase technique. A high or moderate density of immunoreactive cell bodies was found in the superior central nucleus, nucleus incertus, dorsal tegmental nucleus, nucleus of the trapezoid body, and in the laminar spinal trigeminal nucleus, whereas a low density of such perikarya was observed in the inferior colliculus, nucleus praepositus hypoglossi, dorsal nucleus of the raphe, nucleus of the brachium of the inferior colliculus, and in the nucleus of the solitary tract. The highest density of immunoreactive fibers was found in the substantia nigra, dorsal motor nucleus of the vagus, nucleus coeruleus, lateral tegmental field, marginal nucleus of the brachium conjunctivum, and in the inferior and medial vestibular nuclei. These results indicate that alpha-neo-endorphin is widely distributed in the cat brain stem and suggest that the peptide could play an important role in several physiological functions, e.g., those involved in respiratory, cardiovascular, auditory, and motor mechanisms.