Genetic Factors in Susceptibility: Serum PON1 Variation Between Individuals and Species

In mammals, serum paraoxonase (PON1) is tightly associated with high-density lipoprotein (HDL) particles. In human populations, PON1 exhibits a substrate dependent activity polymorphism determined by an Arg/Gln (R/Q) substitution at amino acid residue 192. The physiological role of this protein appears to be involvement in the metabolism of oxidized lipids. Several studies have suggested that the PON1_R192 allele may be a risk factor in coronary artery disease. PON1 also plays an important role in the metabolism of organophosphates including insecticides and nerve agents. The PON1_R192 isoform hydrolyzes paraoxon rapidly, but diazoxon, soman and sarin slowly compared with the PON1_Q192 isoform. Both PON1 isoforms hydrolyze phenylacetate at approximately the same rate, while PON1_R192 hydrolyzes chlorpyrifos oxon slightly faster than PON_Q192. Animal model studies involving injection of purified rabbit PON1 into mice clearly demonstrated the ability of PON1 to protect cholinesterases from inhibition by OP compounds. The consequence of having low PON1 levels has been addressed with toxicology studies in PON1 knockout mice. These mice showed dramatically increased sensitivity to chlorpyrifos oxon, diazoxon and some increased sensitivity to the respective parent compounds. These observations are consistent with earlier studies that showed a good correlation between high rates of OP hydrolysis by serum PON1 and resistance to specific OP compounds. They are also consistent with the observations that newborns have an increased sensitivity to OP toxicity, due in part to their not expressing adult PON1 levels for weeks to months after birth, depending on the species. Together, these studies point out the importance of considering the genetic variability of PON1₁₉₂ isoforms and levels as well as the developmental time course of PON1 appearance in serum in developing risk assessment models     

Diurnal Variation in Scent Marking Behavior in Captive Male and Female Common Marmosets, Callithrix jacchus

Chemical communication by scent-marking behavior in New World primates is used to prevent the access of potential competitors to a territory, to identify food resources and the reproductive condition of mates, among others. In common marmosets, primates of the Callitrichidae family, this behavior also occurs as olfactory identification of an individual or of the reproductive status of females. Despite this information, the diurnal variation and gender differences in the profile of this behavior remain to be investigated. The aims of this study were to establish the diurnal profile of the distribution of this behavior and the influence of the sex of markers. We used 18 adult common marmosets, Callithrix jacchus, 10 males and 8 females from 6 family groups (6 fathers and 4 sons; 4 mothers and 4 daughters). The frequency of scent-marking behavior was recorded for each animal over a period of 8 days, twice a week, for 4 weeks, starting when the animals left the nest box (approximately at 05:00 a.m.) until the end of the photophase, at about 05:00 p.m. A MANOVA test was performed to compare the frequency of scent-marking behavior at 2 hour intervals using pooled data for males and females. The results showed that significantly higher levels of scent-marking behavior occurred during the 03:00-05:00 p.m. interval compared to all other intervals. Lower values were recorded during the 11:00-13:00 interval and an effect of the sex factor was also found, with the values being higher for females than for males, although a significant difference was recorded only for the 07:00-09:00 interval. Minimal values for males were recorded during the 07:00-09:00 interval, whereas minimum values for females were recorded during the 11:00-13:00 interval. However, the highest values for both sexes continued to occur during the 15:00-17:00 interval. These results suggest that scent marking behavior in common marmosets has a preferential incidence at the end of the day and this might be occurring in association with feeding behavior. At this time these animals usually forage more to prepare for the night's fast. Since these animals can discriminate chemical clues as long as 24 hours after they have been left, the higher incidence of this behavior at this time probably will assure that the animals will localize feeding resources used on the preceding day. Significant elevation of scent marking behavior in females in relation to males was found only at 07:00-09:00 interval and seems to be associated with signalizing of reproductive status, preferential access to foraging or both.     

Periodicity of growth rings in some flood-prone trees of the Atlantic Rain Forest in Rio de Janeiro, Brazil

The periodicity of growth ring formation was studied in Tabebuia cassinoides (Lam.) DC, Tabebuia umbellata (Sond.) Sandwith, Symphonia globulifera L., and Alchornea sidifolia Müll. Arg. in a swamp forest within the Atlantic Rain Forest of the state of Rio de Janeiro, southeastern Brazil. Mechanical wounds of the vascular cambium allowed cyclic growth to be observed, and the position of latewood relative to the wounds was analysed. Radial growth was correlated with phenology, temperature, precipitation, photoperiod, flooding regime, and endogenous rhythms. All species showed annual growth rings; however, there were different patterns of radial growth. Phenology was an important factor influencing the activity of the vascular cambium. The period of leaf abscission was correlated with the formation of latewood in three of the species studied, but it occurred at different times for each species. Flooding was a determinant of periodic growth in T. cassinoides; photoperiod was indirectly responsible for radial growth rhythm in T. umbellata, and endogenous rhythms accounted for the radial growth rhythm of S. globulifera and A. sidifolia.     

A dendroclimatological approach to diameter growth in adult cork-oak trees under production

The diameter growth of mature cork oaks under cork production in southwestern Portugal was studied during a 9-year cork-production cycle in relation to fluctuations in precipitation and temperature, and to drought indices combining the two variables. A dendroclimatological approach was applied to the series of 8 complete years contained in the cork-production cycle and growth effects were removed by standardization and calculation of annual growth indices. The most important factor positively influencing diameter growth was cumulative precipitation in the growing season (January-June) and in the previous autumn and winter (October/November of the previous year-June). The monthly temperature is a less influential factor, negatively correlated with diameter growth in high summer drought (August) and positively correlated at the beginning of physiological activity (March).     

The participation of AtXPB1, the XPB/RAD25 homologue gene from Arabidopsis thaliana, in DNA repair and plant development

Nucleotide excision repair in Arabidopsis thaliana differs from other eukaryotes as it contains two paralogous copies of the corresponding XPB/RAD25 gene. In this work, the functional characterization of one copy, AtXPB1, is presented. The plant gene was able to partially complement the UV sensitivity of a yeast rad25 mutant strain, thus confirming its involvement in nucleotide excision repair. The biological role of AtXPB1 protein in A. thaliana was further ascertained by obtaining a homozygous mutant plant containing the AtXPB1 genomic sequence interrupted by a T-DNA insertion. The 3' end of the mutant gene is disrupted, generating the expression of a truncated mRNA molecule. Despite the normal morphology, the mutant plants presented developmental delay, lower seed viability and a loss of germination synchrony. These plants also manifested increased sensitivity to continuous exposure to the alkylating agent MMS, thus suggesting inefficient DNA damage removal. These results indicate that, although the duplication seems to be recent, the features described for the mutant plant imply some functional or timing expression divergence between the paralogous AtXPB genes. The AtXPB1 protein function in nucleotide excision repair is probably required for the removal of lesions during seed storage, germination and early plant development.     

A plant-specific syntaxin-6 protein contributes to the intracytoplasmic route for the begomovirus CabLCV

Because of limited free diffusion in the cytoplasm, viruses must use active transport mechanisms to move intracellularly. Nevertheless, how the plant single-stranded DNA begomoviruses hijack the host intracytoplasmic transport machinery to move from the nucleus to the plasmodesmata remains enigmatic. Here, we identified nuclear shuttle protein (NSP)-interacting proteins from Arabidopsis (Arabidopsis thaliana) by probing a protein microarray and demonstrated that the cabbage leaf curl virus NSP, a facilitator of the nucleocytoplasmic trafficking of viral (v)DNA, interacts in planta with an endosomal vesicle-localized, plant-specific syntaxin-6 protein, designated NSP-interacting syntaxin domain-containing protein (NISP). NISP displays a proviral function, unlike the syntaxin-6 paralog AT2G18860 that failed to interact with NSP. Consistent with these findings, nisp-1 mutant plants were less susceptible to begomovirus infection, a phenotype reversed by NISP complementation. NISP-overexpressing lines accumulated higher levels of vDNA than wild-type. Furthermore, NISP interacted with an NSP-interacting GTPase (NIG) involved in NSP–vDNA nucleocytoplasmic translocation. The NISP–NIG interaction was enhanced by NSP. We also showed that endosomal NISP associates with vDNA. NISP may function as a docking site for recruiting NIG and NSP into endosomes, providing a mechanism for the intracytoplasmic translocation of the NSP–vDNA complex toward and from the cell periphery.     

Identification of a V-type proton pump in the outer mantle epithelium of Anodonta cygnea

The dissected outer mantle epithelium (OME) of Anodonta cygnea, when mounted in Ussing type chambers, generated a spontaneous potential difference of 22.0±12.6 mV and, when short-circuited, a positive current (I_sc) of 30.0±11 μA/cm² towards the shell side and a conductance of 1.1±0.4 mS/cm². When in contact with the shell side, Bafilomycin A₁ and Concanamycin A, specific inhibitors of V-proton pumps, induced 90% inhibition of I_sc in 5 and 35 min, respectively. They had no effect in the current from the hemolymph side. Both drugs induced a dramatic fall in conductance from the shell side. Tributyltin oxide (TBTO) inhibited 90% of the I_sc in 3 min and induced a fall in conductance only from the shell side. Two observations suggest a direct effect on the proton pump: it was effective only from the shell side and the time course of the effect was identical to that of Bafilomicyn A₁. Dicyclohexycarbodiimide (DCCD) and N-ethylmaleimide (NEM) inhibited I_sc from both sides but very slowly and there was a delay of the effect from the hemolymph side in relation to the shell side. Taken together, the results suggest the presence of a V-type proton pump located at the apical (shell side) barrier of the OME.