Phylogeography of the cactophilic species Drosophila gouveai: demographic events and divergence timing in dry vegetation enclaves in eastern Brazil

Aim  The aim of this study was to assess the causal mechanisms underlying populational subdivision in Drosophila gouveai , a cactophilic species associated with xeric vegetation enclaves in eastern Brazil. A secondary aim was to investigate the genetic effects of Pleistocene climatic fluctuations on these environments.
Location  Dry vegetation enclaves within the limits of the Cerrado domain in eastern Brazil.
Methods  We determined the mitochondrial DNA haplotypes of 55 individuals (representing 12 populations) based on sequence data of a 483-bp fragment from the cytochrome c oxidase subunit II (COII) gene. Phylogenetic and coalescent analyses were used to test for the occurrence of demographic events and to infer the time of divergence amongst genetically independent groups.
Results  Our analyses revealed the existence of two divergent subclades (G1 and G2) plus an introgressed clade restricted to the southernmost range of D. gouveai . Subclades G1 and G2 displayed genetic footprints of range expansion and segregated geographical distributions in south-eastern and some central highland regions, east and west of the Paraná River valley. Molecular dating indicated that the main demographic and diversification events occurred in the late to middle Pleistocene.
Main conclusions  The phylogeographical and genetic patterns observed for D. gouveai in this study are consistent with changes in the distribution of dry vegetation in eastern Brazil. All of the estimates obtained by molecular dating indicate that range expansion and isolation pre-dated the Last Glacial Maximum, occurring during the late to middle Pleistocene, and were probably triggered by climatic changes during the Pleistocene. The current patchy geographical distribution and population subdivision in D. gouveai is apparently closely linked to these past events.     

Evaluation of DNA damage induced by norfloxacin in liver and kidney of adult rats and in fetal tissues after transplacental exposure

Norfloxacin, a recently developed antimicrobial fluoroquinolone, was investigated for DNA-damaging activity in rat liver and kidney. After oral administration of single doses ranging from 1 to 8 mmole/kg, DNA fragmentation was absent in liver and kidney both 2 and 6 h after treatment. However, when administered to pregnant rats, the highest doses produced a detectable amount of DNA damage in fetal tissues. This damage appears to be an aspecific consequence of maternal and fetal toxicity rather than a specific genotoxic effect.     

Ly1+ PRO-B lymphocyte clones. Phenotype, growth requirements and differentiation in vitro and in vivo.

Several clones obtained from the bone marrow of a BALB/c mouse were found to contain the heavy and light chain Ig genes in the germline configuration, to express Ly1 and to carry the B cell lineage markers B-220, Lyb8 and BP-1; these clones are Pgp-1+, LFA-1+, J11d+, Mac-1+ and Thy1-, Lyt2-, L3T4-, GM1.2- and Ia-. Three clones analyzed in detail (Lyd9, LyH7 and Lyb9) have receptors for interleukin (IL) 2 and IL3 as assessed with the 7D4 and CC11 monoclonal antibodies respectively. They grow in rIL3 but not in rIL2 or rIL1; both rIL4 and rIL5 also promote their proliferation, albeit to a much lesser extent than rIL3. None of the interleukins tested alone or in various combinations promoted the clones to differentiate in vitro along the B cell pathway. Treatment with 5-Azacytidine (5-Aza) induced cell surface Ia expression but not rearrangement or expression of Ig genes. However, 5-Aza-treated Lyd9, LyH7 and Lyb9 cells co-cultured with X-ray irradiated accessory cells and LPS gave rise to Ly1+, IgM+ B lymphocytes (range 14-51%) including mu + kappa + (78-93%), and mu + lambda + (9-25%) B lymphocytes. In vivo, the Lyd9, LyH7 and Lyb9 clones gave rise to IgM+ B lymphocytes (8.5-17%) including mu + kappa +, and mu + lambda +, but not to Lyt2+ or L3T4+ T lymphocytes after 4-6 weeks of transfer into Scid mice. Our results indicate that Ly1+ IgM+ cells comprise a subpopulation of B lymphocytes that is derived from IL3-responsive Ly1+ PRO-B lymphocytes.     

Nitric oxide from L-arginine stimulates the soluble guanylate cyclase in adrenal glands

The formation of nitric oxide (NO) by an L-arginine:NO synthase and its stimulation of the soluble guanylate cyclase was studied in rat whole adrenal and bovine cortex and medulla cytosol. In the presence of L-arginine, the stimulation of soluble guanylate cyclase was accompanied by the formation of citrulline and NO2-, formed from NO. The NO synthase was NADPH- and Ca(2+)-dependent and was inhibited by several L-arginine analogues. These results indicate that rat and bovine adrenal cytosol contains an L-arginine:NO synthase.     

DNA damage in stomach, kidney, liver and lung of rats treated with atrazine

The genotoxic activity of atrazine, a widely used triazine herbicide, was assayed by the DNA alkaline elution technique in rats given orally a single high dose or repeated daily doses. DNA breaks (and/or alkali-labile lesions) were detected in cell suspensions obtained from stomach, kidney and liver, but not in those from lung.     

Does alternative exon usage contribute to serotonin receptor heterogeneity?

We have previously isolated serotonin 5-HT_1C receptor cDNA clones. In contrast to most other receptors coupled to GTP binding proteins, the 5-HT_1C receptor gene contains several introns in its coding region. A similar exon-intron distribution is found in the 5-HT₂ receptor gene. The presence of large introns tempted us to test whether exchange of exons contributes to serotonin receptor heterogeneity. Therefore, blots with RNAs from different regions of the brain and brain slices were hybridized in situ with probes representing individual exons. We did not find any evidence for the exchange of exons which should result in an unequal distribution of hybridization signals found with the exon-specific probes. With the methodology used we should be able to see differential splicing in the form where individual exons are used alternatively resulting in mRNAs coding for different serotonin receptor types. We would not, however, see if a given exon can be modified by the alternative use of several splice-junctions.     

Effect of Naturally Occurring nif Reiterations on Symbiotic Effectiveness in Rhizobium phaseoli

Most naturally occurring strains of Rhizobium phaseoli possess reiteration of the nif genes. Three regions contain nitrogenase structural genes in strain CFN42. Two of these regions (a and b) have copies of nifH, nifD, and nifK, whereas the third region (c) contains only nifH. Strains containing mutations in either nif region a or nif region b had significantly diminished symbiotic effectiveness compared with the wild-type strain on the basis of nodule mass, total nitrogenase activity per plant, nitrogenase specific activity, total nitrogen in the shoot, and percentage of nitrogen. A strain containing mutations in both nif region a and nif region b was totally ineffective. These data indicate that both nif region a and nif region b are needed for full symbiotic effectiveness in R. phaseoli.     

Narrow- and Broad-Host-Range Symbiotic Plasmids of Rhizobium spp. Strains That Nodulate Phaseolus vulgaris

Agrobacterium transconjugants containing symbiotic plasmids from different Rhizobium spp. strains that nodulate Phaseolus vulgaris were obtained. All transconjugants conserved the parental nodulation host range. Symbiotic (Sym) plasmids of Rhizobium strains isolated originally from P. vulgaris nodules, which had a broad nodulation host range, and single-copy nitrogenase genes conferred a Fix⁺ phenotype to the Agrobacterium transconjugants. A Fix⁻ phenotype was obtained with Sym plasmids of strains isolated from P. vulgaris nodules that had a narrow host range and reiterated nif genes, as well as with Sym plasmids of strains isolated from other legumes that presented single nif genes and a broad nodulation host range. This indicates that different types of Sym plasmids can confer the ability to establish an effective symbiosis with P. vulgaris.     

Nitrogen Source Regulates Glutamate Dehydrogenase NADP Synthesis in Neurospora crassa

Neurospora crassa glutamate dehydrogenase-NADP (EC 1.3.1.3) has a higher activity when mycelium is grown on ammonium or nitrate as nitrogen source than when grown on glutamate or glutamine. Quantitative immunoelectrophoresis established that, under all conditions, enzyme activity corresponded to enzyme concentration. Isotope incorporation studies demonstrated that the nitrogen source exerts its regulation at the level of de novo enzyme synthesis.