Close karyological kinship between the reptilian suborder serpentes and the class aves

Summary In contrast to the situation found in two classes of warm-blooded vertebrates, mammals and birds, the class Reptilia is not uniform with regard to total genetic content; rather, it contains two distinct categories. The close cytological kinship between snakes and birds was revealed. Both are almost identical in total genetic content, which is about 50 per cent that of placental mammals. Both have microchromosomes, as well as Z-chromosomes very similar in absolute size, comprising nearly 10 per cent of the homogametic haploid (AZ) set. This leads to the implication that snakes and birds originated from the same lineage, and that their Z-chromosomes have not changed substantially since the Jurassic period of the Mesozoic era, about 180 million years ago.Within the reptilian suborder Serpentes, the step-by-step differentiation from the primitive ZW pair to the grossly heteromorphic ZW pair could be observed. In the ancient family Boidae, the sex chromosomes were still homomorphic to each other. In the family Colubridae, the beginning of heteromorphism was manifested in two ways. In some species, a pericentric inversion on the W caused it to differ from the Z; in others, duplication of the W occurred. In the family Crotalidae, the W had apparently achieved its very specialized status; it was a distinctly smaller element.In Säo Paulo, this work was supported by Fundacão de Amparo a Pesquisa do Estado de São Paulo e Fundo de Pesquisas do Instituto Butantan. In Duarte, this work was supported in part by grant CA-05138-05, National Cancer Institute, U. S. Public Health Service. Contribution No. 36-64, Department of Biology, City of Hope Medical Center.     

Relationships of the chromosomal species in the eurasian mole rats of theSpalax ehrenbergi group as determined by DNA-DNA hybridization,and an estimate of the spalacid-murid divergence time

Summary DNA-DNA hybridization was used to measure the average genomic divergence among the four chromosomal species of the Eurasian mole rats belonging to theSpalax ehrenbergi complex (Rodentia: Spalacidae). The percent nucleotide substitutions in the single-copy nuclear DNA among the species ranged from 0 to 5%, suggesting that speciation has occurred with minor genomic changes in these animals. The youngest chromosomal species appear to differ by 0.2–0.6% base pair mismatch, which is only between one and three base differences in a 500-bp fragment. The interspecific values of percent nucleotide differences permit the recognition of two well-separated speciation events in theS. ehrenbergi complex, the older (of Lower Pleistocene age) having isolated the chromosomal species 2n=54 before the divergence of the three other species.DNA-DNA hybridization was also used to compare the Spalacinae (Eurasian mole rats), Murinae (Old World rats and mice), and Arvicolinae (voles and lemmings). These data enabled us to estimate the time of divergence of the spalacids at ca. 19 million years ago. The dates of divergence among the other rodent lineages, as predicted by DNA hybridization results, agree well with paleontological data. These dates of divergence are obtained by the relation between geological time and single-copy nuclear DNA change, a relation that was calibrated by Catzeflis et al. (1987) through the use of fossil Arvicolinae and Murinae data.     

Macromolecular adducts of ethylene oxide: a literature review and a time-course study on the formation of 7-(2-hydroxyethyl) guanine following exposures of rats by inhalation

The results of efforts to identify and quantify macromolecular adducts of ethylene oxide (ETO), to determine the source and significance of background levels of these adducts, and to generate molecular dosimetry data on these adducts are reviewed. A time-course study was conducted to investigate the formation and persistence of 7-(2-hydroxyethyl)guanine (7-HEG; Fig. 1) in various tissues of rats exposed to ETO by inhalation, providing information necessary for designing investigations on the molecular dosimetry of adducts of ETO. Male F344 rats were exposed 6 h/day for up to 4 weeks (5 days/wk) to 300 ppm ETO by inhalation. Another set of rats was exposed for 4 weeks to 300 ppm ETO, and then killed 1–10 days after cessation of exposures. DNA samples from control and treated rats were analyzed for 7-HEG using neutral thermal hydrolysis, HPLC separation, and fluorescence detection. The adduct was detectable in all tissues of treated rats following 1 day of ETO exposure and increased approximately linearly for 3–5 days before the rate of increase began to level off. Concentrations of 7-HEG were greatest in brain, but the extent of formation was similar in all tissues studied. The adduct disappeared slowly from DNA, with an apparent half-life approx. 7 days. The shape of the formation curve and the in vivo half-life indicate that 7-HEG will approach steady-state concentrations in rat DNA by 28 days of ETO exposure. The similarity in 7-HEG formation in target and nontarget tissues indicates that the tissue specificity for tumor induction is due to factors in addition to DNA-adduct formation.     

Functional analysis of a complex oncogene arrangement in biotype III Agrobacterium tumefaciens strains

The ubiquitous grapevine-associated octopine/cucumopine Ti plasmids of biotype III Agrobacterium tumefaciens strains carry two T regions, TA and TB, with a complex oncogene arrangement. Within the octopine/cucumopine group, two main strain types were identified: large TA strains with a TA region resembling the TL region of the biotype I octopine strain Ach5 and small TA strains with a similar T region organization as the large TA strains but with a large internal TA deletion. Structural and functional studies of the representative large TA strain Tm4 revealed six oncogenes. Each oncogene was inserted in a disarmed vector and tested for biological activity using the corresponding oncogenes of Ach5 as standards. Five Tm4 oncogenes, TA-iaaM, T-ipt, T-6b, TB-iaaH and TB-iaaM, were shown to be active, the IS-interrupted TA-iaaH gene was inactive. To study the role of each gene in the pTiTm4 context, several single and multiple pTiTm4 mutations were constructed. It was shown that whereas TA-iaaM and TB-iaaH are essential for tumour formation on grapevine, T-ipt, T-6b and TB-iaaM are not. The avirulence of the TA-iaaM ^- mutant was shown to be due to an inhibitory effect of the T-ipt gene, since a TA-iaaM ^- /T-ipt ^- double mutant was fully virulent. We conclude that the TA-iaaM gene of large TA strains is specifically required to counteract the tumour growth inhibiting activity of the T-ipt gene. Both TA-iaaM and T-ipt are absent from the small TA strains. A model on the roles and interactions of the different oncogenes in large TA and small TA strains is presented.     

Functional Expression of P-Glycoprotein in an Immortalised Cell Line of Rat Brain Endothelial Cells, RBE4

Abstract: The presence of P-glycoprotein in the cell plasma membrane limits the penetration of many cytotoxic substances into cells that express the gene product. There is considerable evidence also to indicate that P-glycoprotein is expressed as part of the normal blood-brain barrier in the luminal membranes of the cerebral capillary endothelial cells, where it presumably performs a protective function for the brain. This report describes the functional expression of P-glycoprotein in an immortalised cell line, RBE4, derived from rat cerebral capillary endothelial cells. The expression of P-glycoprotein is demonstrated by western immunoblotting and by immunogold and fluorescent staining with monoclonal antibodies. The cellular accumulation of [³H]colchicine and [³H]vinblastine is investigated and shown to be enhanced by the presence of azidothymidine, chlorpromazine, verapamil, cyclosporin A, and PSC 833 ([3'-keto-Bmt¹]-[Val²]-cyclosporin) at 50 or 100 µ M concentration. It is concluded that the RBE4 cell line is a valuable tool for investigating the mechanisms of P-glycoprotein activity both in the blood-brain barrier and in multidrug resistance in general.     

Alkaloid level in narrow-leafed lupin, Lupinus angustifolius, influences green peach aphid reproductive performance

Two viviparous parthenogenetic clones of the green peach aphid, Myzus persicae (Sulzer), one collected from Rydalmere, New South Wales (NSW), and the other from South Perth (SP), Western Australia, were reared on radish, Raphanus sativus L. cv. Scarlet Globe, under controlled conditions. The NSW clone was fed on simple artificial diets containing alkaloid extracted from narrow-leafed lupin, Lupinus angustifolius L. cv. Fest., and its reproductive performance monitored over 112 h. Forty (40) h into the experiment and thereafter, aphids on the control diet (sucrose solution) produced significantly more offspring (P<0.05) than those on diets containing alkaloid. In a separate experiment, apterae of each clone were caged on three lines (cv. Yorrel, cv. Danja and 84L:441) of narrow-leafed lupin, and allowed to reproduce. The first three offspring were retained, and all developed to 3rd or 4th instar stage. Two nymphs were removed, and the remaining nymph reared through. All three lines produced adults. The number of young produced were counted over 11 days. Fecundity of the SP clone was lower on line 84L:441, but there was no difference in the fecundity of the NSW clone. Phloem exudate and green tissue was concomitantly collected from all lines, and analysed by GC-MS for the alkaloids lupanine and 13-hydroxylupanine. Line 84L:441 contained the highest level of total alkaloids in both phloem and tissue. All experiments indicate that alkaloid level may suppress fecundity of green peach aphids.     

Decomposition of Eucalyptus globulus leaves and three native leaf species (Alnus glutinosa, Castanea sativa and Quercus faginea) in a Portuguese low order stream

Leaf decomposition of the exotic evergreen Eucalyptus globulus (eucalyptus), and three native deciduous tree species, Alnus glutinosa (alder), Castanea sativa (chestnut) and Quercus faginea (oak), was compared in a second order stream in Central Portugal. Changes in dry weight, nitrogen and polyphenolic compounds and microbial colonization were periodically assessed for three months.Negative exponential curves fit the leaf weight loss with time for all leaf species. Mass loss rate was in the order alder (K = 0.0161) > chestnut (K = 0.0079) > eucalyptus (K = 0.0068) > oak (K = 0.0037). Microbial colonization followed the same pattern as breakdown rates. Evidence of fungal colonization was observed in alder after 3 days in the stream, whereas it took 21 days in oak leaves to have fungal colonization. Fungal diversity was leaf species-dependent and increased with time. In all cases, percent nitrogen per unit leaf weight increased, at least, at the initial stages of decay while soluble polyphenolics (expressed as percentage per unit leaf weight) decreased rapidly in the first month of leaves immersion.Intrinsic factors such as nitrogen and polyphenolic content may explain differences in leaf decomposition. The possible incorporation of eucalyptus litter into secondary production in a reasonable time span is suggested, although community balance and structure might be affected by differences in allochthonous patterns determined by eucalyptus monocultures.     

Effects of eucalyptus afforestation on leaf litter dynamics and macroinvertebrate community structure of streams in Central Portugal

To test the hypothesis whether afforestation with Eucalyptus globulus affects litter dynamics in streams and the structure of macroinvertebrate aquatic communities, we compared streams flowing through eucalyptus and deciduous forests, paying attention to: (i) litterfall dynamics, (ii) accumulation of organic matter, (iii) processing rates of two dominant leaf species: eucalyptus and chestnut, and (iv) macroinvertebrate community structure. The amount of allochthonous inputs was similar in both vegetation types, but the seasonality of litter inputs differed between eucalyptus and natural deciduous forests. Eucalyptus forest streams accumulated more organic matter than deciduous forest streams. Decomposition of both eucalyptus and chestnut leaf litter was higher in streams flowing through deciduous forests. The eucalyptus forest soils were highly hydrophobic resulting in strong seasonal fluctuations in discharge. In autumn the communities of benthic macroinvertebrates of the two stream types were significantly different. Deciduous forest streams contained higher numbers of invertebrates and more taxa than eucalyptus forest streams. Mixed forest streams (streams flowing through eucalyptus forests but bordered by deciduous vegetation) were intermediate between the two other vegetation types in all studied characteristics (accumulation of benthic organic matter, density and diversity of aquatic invertebrates). These results suggest that monocultures of eucalyptus affect low order stream communities. However, the impact may be attenuated if riparian corridors of original vegetation are kept in plantation forestry.