Influence of vertical and mechanical transmission on the dynamics of dengue disease

We formulate a non-linear system of differential equations that models the dynamics of transmission of dengue fever. We consider vertical and mechanical transmission in the vector population, and study the effects that they have on the dynamics of the disease. A qualitative analysis as well as some numerical examples are given for the model.     

Zinc uptake by human placental microvillous membrane vesicles

Zinc uptake by syncytiotrophoblast microvillous membrane vesicles (SMMV) from human placentas was characterized and the effects of maternal serum zinc levels at term and of gestational age on kinetic parameters were evaluated. Zinc uptake at pH 7.2 was rapid for the first 2 min, followed by a slower increase, approaching equilibrium after 30 min. Uptake was saturable at a zinc concentration of 30 micromol/L, higher than the upper range of the physiological serum zinc level. Kinetic analysis of uptake at 1 min in SMMV from term placenta showed similar Km values (mean: 6.9+/-0.6 micromol/L) for different levels of maternal serum zinc. However, Vmax was higher (p < 0.05) in SMMV from mothers with serum zinc lower than 7.6 micromol/L compared to those with higher serum zinc levels (35.8+/-1.6 and 26.6+/-1.6 nmol 65Zn/mg protein/min, respectively). Km values were similar in term (>37 wk of gestation) and preterm (20-25 wk of gestation) placentas, whereas Vmax was higher (p < 0.05) in the preterm (34.3+/-1.6 nmol Zn/mg protein/min) compared to term placentas from mothers with serum zinc levels above 7.6 micromol/L. These results suggest that whereas afffinity for zinc was not altered with gestational age or maternal serum zinc levels, zinc-uptake capacity in human placenta is influenced both by gestational age and by low levels of maternal serum zinc in order to ensure an adequate maternal-fetal zinc transfer.     

A new species of Sanicula L. (Umbelliferae/Apiaceae) endemic to Baja California, Mexico

A new species of the genusSanicula (sect.Sanicoria) endemic to the southern Sierra Juárez of Baja California, Mexico, is described and illustrated.Sanicula moranii resemblesS. deserticola andS. bipinnatifida, but has thicker basal leaves, with broader petioles and rachises, and shorter fruit prickles that are confined to the apical part of the mericarps. The taxonomic relationships of these species are discussed, along with aspects of their distribution and habitat.

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Resumen  Una neuva especie del géneroSanicula (secciónSanicoria) endémica de la Sierra Juárez de Baja California, México, es descrita e ilustrada.Sanicula moranii presenta similitud conS. deserticola yS. bipinnatifida, no obstante tiene gruesas hojas basales con pecíolos y raquis anchos, y espínulas del fruto más cortas que se distribuyen únicamente en la parte apical de los mericarpos. Además, se comentan las relaciones taxonómicas de las tres especies, así como algunos aspectos de sus distribuciones y hábitats.

     

Exopolysaccharide production by the cyanobacterium Anabaena sp. ATCC 33047 in batch and continuous culture

The halotolerant, filamentous, heterocystous cyanobacterium Anabaena sp. ATCC 33047 released, during the stationary growth phase in batch culture and, at low dilution rate, in continuous culture, large amounts of an exopolysaccharide (EPS) to the culture medium. Different environmental, nutritional and physical parameters affected production and accumulation of the EPS. The presence of either a combined nitrogen source or NaCl at high concentration led to decreased EPS production, without affecting cell growth. In contrast, generation of the EPS was markedly enhanced in response to an increase in either air flow rate, temperature or irradiance. In continuous culture, accumulation of EPS in the medium increased in response to a decrease in the dilution rate, with maximal EPS productivity being reached at a dilution rate of 0.03 h⁻¹.     

Multifactorial Modulation of TRH Metabolism

1. Thyrotropin releasing hormone (TRH), synthesized in the paraventricular nucleus of the hypothalamus (PVN), is released in response to physiological stimuli through medianeminence nerve terminals to control thyrotropin or prolactin secretion from the pituitary.2. Several events participate in the metabolism of this neuropeptide: regulation of TRH biosynthesis and release as well as modulation of its inactivation by the target cell.3. Upon a physiological stimulus such as cold stress or suckling, TRH is released and levels of TRH mRNA increase in a fast and transient manner in the PVN; a concomitant increase in cfos is observed only with cold exposure.4. Hypothalamic cell cultures incubated with cAMP or phorbol esters show a rise in TRH mRNA levels; dexamethasone produces a further increase at short incubation times.TRH mRNA are thus controlled by transsynaptic and hormonal influences.5. Once TRH is released, it is inactivated by a narrow specificity ectoenzyme, pyroglu-tamyl peptidase II (PPII).6. In adenohypophysis, PPII is subject to stringent control: positive by thyroid hormones and negative by TRH; other hypothalamic factors such as dopamine and somatostatin also influence its activity.7. These combined approaches suggest that TRH action is modulated in a coordinate fashion.     

Variation in sclerophylly among Iberian populations of Quercus coccifera L. is associated with genetic differentiation across contrasting environments

Evergreen oaks are an emblematic element of the Mediterranean vegetation and have a leaf phenotype that seems to have remained unchanged since the Miocene. We hypothesise that variation of the sclerophyll phenotype among Iberian populations of Quercus coccifera is partly due to an ulterior process of ecotypic differentiation. We analysed the genetic structure of nine Iberian populations using ISSR fingerprints, and their leaf phenotypes using mean and intracanopy plasticity values of eight morphological (leaf angle, area, spinescence, lobation and specific area) and biochemical traits (VAZ pool, chlorophyll and β-carotene content). Climate and soil were also characterised at the population sites. Significant genetic and phenotypic differences were found among populations and between NE Iberia and the rest of the populations of the peninsula. Mean phenotypes showed a strong and independent correlation with both genetic and geographic distances. Northeastern plants were smaller, less plastic, with smaller, spinier and thicker leaves, a phenotype consistent with the stressful conditions that prevailed in the steppe environments of the refugia within this geographic area during glaciations. These genetic, phenotypic, geographic and environmental patterns are consistent with previously reported palaeoecological and common evidence. Such consistency leads us to conclude that there has been a Quaternary divergence within the sclerophyllous syndrome that was at least partially driven by ecological factors.     

Evolutionary transitions of style polymorphisms in Lithodora (Boraginaceae)

Floral polymorphisms provide suitable model systems to test hypotheses concerning the evolution of outbreeding in plants. Although heterostyly has evolved in more than 28 angiosperm families, the evolutionary pathways involving related floral conditions have not yet been fully resolved. In this study, the reconstruction of ancestral states of style polymorphism, with both parsimony and maximum likelihood methods, was carried out for Boraginaceae species in the tribe Lithospermeae, particularly in the genus Lithodora sensu lato, where species present a wide variety of stylar conditions. Detailed floral morphometric analysis confirm different types of style polymorphism within Lithodora. They also reveal a novel style polymorphism (relaxed style dimorphism) in which anther height is variable within a flower (each anther being at a different height), which contrasts to regular distyly (constant anther height within flowers). Style monomorphism is likely to be the ancestral condition in Lithospermeae where the evolution of distyly has occurred several times. Style dimorphism is probably ancestral to distyly, as predicted by certain evolutionary models proposed for heterostyly. However, a reversion from distyly to style dimorphism also appears to occur in this tribe. This is the first documented occurrence of such a transition. This secondary style dimorphism is of the relaxed type and demonstrates the labile nature of floral polymorphisms, which are not necessarily a transition towards heterostyly. We discuss the selective forces involved in the evolution, maintainance and loss of style polymorphisms.     

Life-cycle modification in open oceans accounts for genome variability in a cosmopolitan phytoplankton

Emiliania huxleyi is the most abundant calcifying plankton in modern oceans with substantial intraspecific genome variability and a biphasic life cycle involving sexual alternation between calcified 2N and flagellated 1N cells. We show that high genome content variability in Emiliania relates to erosion of 1N-specific genes and loss of the ability to form flagellated cells. Analysis of 185 E. huxleyi strains isolated from world oceans suggests that loss of flagella occurred independently in lineages inhabiting oligotrophic open oceans over short evolutionary timescales. This environmentally linked physiogenomic change suggests life cycling is not advantageous in very large/diluted populations experiencing low biotic pressure and low ecological variability. Gene loss did not appear to reflect pressure for genome streamlining in oligotrophic oceans as previously observed in picoplankton. Life-cycle modifications might be common in plankton and cause major functional variability to be hidden from traditional taxonomic or molecular markers.     

Pharmacological Blockade of Cannabinoid CB1 Receptors in Diet-Induced Obesity Regulates Mitochondrial Dihydrolipoamide Dehydrogenase in Muscle

Cannabinoid CB₁ receptors peripherally modulate energy metabolism. Here, we investigated the role of CB₁ receptors in the expression of glucose/pyruvate/tricarboxylic acid (TCA) metabolism in rat abdominal muscle. Dihydrolipoamide dehydrogenase (DLD), a flavoprotein component (E3) of α-ketoacid dehydrogenase complexes with diaphorase activity in mitochondria, was specifically analyzed. After assessing the effectiveness of the CB₁ receptor antagonist AM251 (3 mg kg^-1, 14 days) on food intake and body weight, we could identified seven key enzymes from either glycolytic pathway or TCA cycle—regulated by both diet and CB₁ receptor activity—through comprehensive proteomic approaches involving two-dimensional electrophoresis and MALDI-TOF/LC-ESI trap mass spectrometry. These enzymes were glucose 6-phosphate isomerase (GPI), triosephosphate isomerase (TPI), enolase (Eno3), lactate dehydrogenase (LDHa), glyoxalase-1 (Glo1) and the mitochondrial DLD, whose expressions were modified by AM251 in hypercaloric diet-induced obesity. Specifically, AM251 blocked high-carbohydrate diet (HCD)-induced expression of GPI, TPI, Eno3 and LDHa, suggesting a down-regulation of glucose/pyruvate/lactate pathways under glucose availability. AM251 reversed the HCD-inhibited expression of Glo1 and DLD in the muscle, and the DLD and CB₁ receptor expression in the mitochondrial fraction. Interestingly, we identified the presence of CB₁ receptors at the membrane of striate muscle mitochondria. DLD over-expression was confirmed in muscle of CB ₁ ^-/- mice. AM251 increased the pyruvate dehydrogenase and glutathione reductase activity in C₂C₁₂ myotubes, and the diaphorase/oxidative activity in the mitochondria fraction. These results indicated an up-regulation of methylglyoxal and TCA cycle activity. Findings suggest that CB₁ receptors in muscle modulate glucose/pyruvate/lactate pathways and mitochondrial oxidative activity by targeting DLD.