Dengue Virus RNA Structure Specialization Facilitates Host Adaptation

Many viral pathogens cycle between humans and insects. These viruses must have evolved strategies for rapid adaptation to different host environments. However, the mechanistic basis for the adaptation process remains poorly understood. To study the mosquito-human adaptation cycle, we examined changes in RNA structures of the dengue virus genome during host adaptation. Deep sequencing and RNA structure analysis, together with fitness evaluation, revealed a process of host specialization of RNA elements of the viral 3’UTR. Adaptation to mosquito or mammalian cells involved selection of different viral populations harvesting mutations in a single stem-loop structure. The host specialization of the identified RNA structure resulted in a significant viral fitness cost in the non-specialized host, posing a constraint during host switching. Sequence conservation analysis indicated that the identified host adaptable stem loop structure is duplicated in dengue and other mosquito-borne viruses. Interestingly, functional studies using recombinant viruses with single or double stem loops revealed that duplication of the RNA structure allows the virus to accommodate mutations beneficial in one host and deleterious in the other. Our findings reveal new concepts in adaptation of RNA viruses, in which host specialization of RNA structures results in high fitness in the adapted host, while RNA duplication confers robustness during host switching.     

Neuronal gene expression in aluminum myelopathy

1. Aluminum administration to susceptible animal species results in neurofilament accumulation in neuronal perikarya and proximal axons. Pathogenetic studies in vivo have shown that aluminum rapidly associates with neuronal chromatin. Whether the effect of aluminum on DNA components plays a role in the production of the neurofibrillary lesion remains unclear. 2. In this study we used Northern analysis and in situ hybridization to evaluate mRNA levels of specific neuronal and glial components in the rabbit spinal cord at various times following aluminum administration. 3. Our results show that (a) all neuronal mRNAs evaluated (neurofilament triplet components, neuronal-specific enolase, and amyloid precursor protein) are markedly decreased, with no decrease in glial fibrillary acidic protein; (b) the effect on neuronal gene expression occurs early and concurrently with the development of the neurofibrillary lesion and reverses rapidly after a single dose of aluminum; and (c) there is a direct correlation between the severity of the neurofibrillary lesion and the decrease in neuronal mRNA levels. 4. We interpret our results to mean that the accumulation of neurofilaments in this model is not due to a selective effect on neurofilament gene expression but may be due to an inhibition of genes coding for components involved in processing of neurofilament proteins.     

The daily variations of airborne fungal spores in Mexico City

The daily and seasonal distribution of airborne fungal particles was recorded in a high altitude tropical zone. Sampling was carried out in the southern part of Mexico City. An Andersen air sampler was used over a period of six months. Ten minutes sampling for each set of plates was done at fixed schedule: 07:30, 14:00 and 19:00 hours. The sampler was placed 10 m above the ground. Daily variation was found to be associated with the season, weather and atmospheric stability. The highest value of mold counts (3195 CFU m⁻³) was recorded in the evening on October, a transitional month between the rainy and the dry seasons, the lowest (45 CFU m⁻³) at noon during the rainy season. Mold counts were significantly correlated with temperature, having negative signs both in the morning and at noon, and being positive in the evening. The abundance of only three genera was recorded.Cladosporium, was isolated more frequently, and its abundance at 14:00 h was of 38%;Alternaria represented 4.0%, at 14:00 h, andAspergillus 3.0% at 7:30 h. Fifteen species belonging to the latter genera were identified and most of them are considered as opportunistic molds of clinical significance.     

Cytogenetics of the European plethodontid salamanders of the genus Hydromantes (Amphibia,Urodela)

A karyological analysis was carried out on different European species of the genus Hydromantes (Plethodontidae). All the species examined share the same chromosome number (2n=28) and, with the exception represented by pair XIV, morphologically similar karyotypes. While the karyotypes display a similar distribution — mainly centromeric and pericentric — of C-heterochromatin, quantitative variations in pericentric heterochromatin are observed among species. In the continental species Hydromantes italicus and ambrosii as well as in the eastern Sardinian species imperialis, flavus and specie nova, pair XIV consists of heteromorphic sex chromosomes of the XX/XY type. It is proposed that the differentiation of the Y might have taken place through the occurrence of a structural rearrangement, such as a pericentric inversion, starting from a hypothetical, homomorphic pair XIV. A sex-related heteromorphism is not found in the western Sardinian species H. genei. A further karyological differentiation among these species concerns the position of the nucleolus organizing region (NOR), which is located on chromosome XII (H. italicus and ambrosii) or on chromosome X, close to the centromere (H. genei, H. imperialis and H. specie nova), or in an intercalary position (H. flavus). The location and the number of the 5 S DNA sites have been conserved during species divergence. On the basis of these karyological data, as well as of results obtained through a preliminary restriction enzyme analysis of the ribosomal and genomic DNAs, the phyletic relationships among the European Hydromantes species are discussed.     

Carbon tetrachloride-induced inhibition of hepatocyte lipoprotein secretion: functional impairment of Golgi apparatus in the early phases of such injury

Functional change of liver Golgi apparatus during carbon tetrachloride (CCl4) poisoning was demonstrated both in rat isolated hepatocytes and in the whole animal. The "in vitro" experimental model provided evidence of Golgi derangement early after giving the haloalkane. The "in vivo" analyses also showed that such an alteration involves both formative and secretory sides of the subcellular structure.     

Molecular organisation of the genes involved in the production of F7(2) fimbriae, causing mannose-resistant haemagglutination, of a uropathogenic Escherichia coli 06:K2:H1:F7 strain

Summary The genes responsible for the formation of the F7₂ fimbriae of the uropathogenic E. coli strain AD110 (O6:K2:H1:F7) have been cloned on the recombinant plasmid pPIL110-35 (Van Die et al. 1983). The F7₂ fimbriae, like the F7₁ fimbriae of AD110, are responsible for mannose resistant haemagglutination (MRHA).The molecular organisation of the genes of pPIL110-35 involved in the expression of MRHA was studied by: (a) analysis of transposon and Tn5 insertion mutants. Mutations that cause an MRHA-deficient phenotype were located in discrete groups within an 11.5 kb restriction fragment of pPIL110-35, separated by insertion mutations that do not inactivate MRHA. (b) complementation experiments. Restriction fragments of pPIL110-35 subcloned in the vector pBR322 were tested for their ability to complement transposon insertion mutations in the corresponding regions of pPIL110-35. Five complementation groups were distinguished.Five genes (designated A-E) involved in the expression of MRHA can be distinguished by these results. The products of these genes were analysed in minicells. The results indicate that gene B codes for a 75 K dalton protein, gene C for a 23 K dalton protein and gene E for a 36 K dalton protein. No product of gene D was observed. Gene A probably codes for the 17 K dalton subunit polypeptide of the F7₂ fimbriae, as will be discussed.     

"In vitro" effect of CCl4, PG and EDTA on GSH levels at different time of incubation of rat liver homogenates

During CCl4-induced lipid peroxidation GSH content in total homogenate from rat liver falls very rapidly in the first 30 min. of incubation "in vitro". CCl4 does not enhance the decrease in total glutathione (TG) during the incubation time, so GSH loss is mainly due to its oxidation to GSSG. On the contrary PG and EDTA, two substances decreasing lipid peroxidation rate, are able to decrease GSH oxidation, without affecting TG content. At 25 degrees C EDTA and PG completely prevent GSH decrease at pH 7.4, while at pH 6 PG affords only a partial prevention. At 37 degrees C both compounds are able to limit GSH decrease at a large extent. Lipid peroxidation seems to have a great importance in the kinetics of GSH decrease and GSSG formation, at least "in vitro". It is noteworthy that PG which inhibits lipid peroxidation stimulated by CCl4 is also able to limit the high GSH loss observed in the homogenates incubated in the presence of halogeno-alkane.     

Enhancement of extractable ethylene at light/dark transition in primary leaves of paclobutrazol-treated Phaseolus vulgaris seedlings

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol], a triazole growth retardant, increased the 1-aminocyclopropane-1-carboxylic acid (ACC) level and resulted in reduced ethylene production, estimated as ethylene release in a closed system or by vacuum-extraction, in the primary leaves of Phaseolus vulgaris L. cv. Juliska seedlings exposed to light. At the light/dark transition, a definite enhancement of the endogenous ethylene level was observed by vacuum-extraction of primary leaves of treated plants and the ethylene deficiency of retardant-treated leaves ceased. The concentration of ACC after the light/dark transition followed the pattern for ethylene, and the increase in ACC content was paralleled by a decrease in malonyl-ACC.
It is concluded that the internal level of ethylene is not necessarily lower in the primary leaves of paclobutrazol-treated bean plants, but under special environmental conditions in vivo it may reach that of the control.