Dual role for tomato heat shock protein 21: protecting photosystem II from oxidative stress and promoting color changes during fruit maturation

The tomato (Lycopersicon esculentum) chloroplast small heat shock protein (sHSP), HSP21, is induced by heat treatment in leaves, but also under normal growth conditions in developing fruits during the transition of chloroplasts to chromoplasts. We used transgenic tomato plants constitutively expressing HSP21 to study the role of the protein under stress conditions and during fruit maturation. Although we did not find any effect for the transgene on photosystem II (PSII) thermotolerance, our results show that the protein protects PSII from temperature-dependent oxidative stress. In addition, we found direct evidence of the protein's role in fruit reddening and the conversion of chloroplasts to chromoplasts. When plants were grown under normal growth temperature, transgenic fruits accumulated carotenoids earlier than controls. Furthermore, when detached mature green fruits were stored for 2 weeks at 2 degrees C and then transferred to room temperature, the natural accumulation of carotenoids was blocked. In a previous study, we showed that preheat treatment, which induces HSP21, allowed fruit color change at room temperature, after a cold treatment. Here, we show that mature green transgenic fruits constitutively expressing HSP21 do not require the heat treatment to maintain the ability to accumulate carotenoids after cold storage. This study demonstrates that a sHSP plays a role in plant development under normal growth conditions, in addition to its protective effect under stress conditions.     

Near-bottom depletion of zooplankton over coral reefs: III: vertical gradient of predation pressure

Many diurnal planktivorous fish in coral reefs efficiently consume zooplankton drifting in the overlying water column. Our survey, carried out at two coral reefs in the Red Sea, showed that most of the diurnal planktivorous fish foraged near the bottom, close to the shelters from piscivores. The planktivorous fish were order of magnitude more abundant near (<1.5 m) the bottom than higher in the water column. The predation pressure exerted by these fish was assessed by measuring the consumption of brine shrimps tethered at different heights above the bottom on a vertical line which was pulled over the reef. Below 1.5 m above bottom, the shrimps survival probability sharply decreased toward the bottom. Higher in the water column, survivorship was nearly 100% with little vertical variation. Our results indicate that near-bottom depletion of zooplankton in coral reefs is likely due to intense predation at that boundary layer. Risk of predation by piscivorous fish apparently restricts planktivorous fish to forage near the bottom, with a distribution pattern greatly deviating from ideal-free distribution.     

Destabilization of tetraplex structures of the fragile X repeat sequence (CGG)n is mediated by homolog-conserved domains in three members of the hnRNP family

Hairpin or tetrahelical structures formed by a d(CGG)_n sequence in the FMR1 gene are thought to promote expansion of the repeat tract. Subsequent to this expansion FMR1 is silenced and fragile X syndrome ensues. The injurious effects of d(CGG)_n secondary structures may potentially be countered by agents that act to decrease their stability. We showed previously that the hnRNP-related protein CBF-A destabilized G′2 bimolecular tetraplex structures of d(CGG)_n. Analysis of mutant proteins revealed that the CBF-A-conserved domains RNP1₁ and ATP/GTP binding box were sufficient and necessary for G′2 d(CGG)_n disruption while the RNP2₁ motif inhibited the destabilization activity. Here, we report that a C-terminal fragment of CBF-A whose only remaining conserved domain was the ATP/GTP binding motif, disrupted G′2 d(CGG)_n more selectively than wild-type CBF-A. Further, two additional members of the hnRNP family, hnRNP A2 and mutant hnRNP A1 effectively destabilized G′2 d(CGG)_n. Examination of mutant hnRNP A2 proteins revealed that, similar to CBF-A, their RNP1₁ element and ATP/GTP binding motif mediated G′2 d(CGG)_n disruption, while the RNP2₁ element blocked their action. Similarly, the RNP1₁ and RNP2₁ domains of hnRNP A1 were, respectively, positive and negative mediators of G′2 d(CGG)_n destabilization. Last, employing the same conserved motifs that mediated disruption of the DNA tetraplex G′2 d(CGG)_n, hnRNP A2 destabilized r(CGG)_n RNA tetraplex.     

The retinal pigment epithelium as a gateway for monocyte trafficking into the eye

The choroid plexus epithelium within the brain ventricles orchestrates blood‐derived monocyte entry to the central nervous system under injurious conditions, including when the primary injury site is remote from the brain. Here, we hypothesized that the retinal pigment epithelium (RPE) serves a parallel role, as a gateway for monocyte trafficking to the retina following direct or remote injury. We found elevated expression of genes encoding leukocyte trafficking determinants in mouse RPE as a consequence of retinal glutamate intoxication or optic nerve crush (ONC). Blocking VCAM‐1 after ONC interfered with monocyte infiltration into the retina and resulted in a local pro‐inflammatory cytokine bias. Live imaging of the injured eye showed monocyte accumulation first in the RPE, and subsequently in the retina, and peripheral leukocytes formed close contact with the RPE. Our findings further implied that the ocular milieu can confer monocytes a phenotype advantageous for neuroprotection. These results suggest that the eye utilizes a mechanism of crosstalk with the immune system similar to that of the brain, whereby epithelial barriers serve as gateways for leukocyte entry.     

Respiratory system stability and abnormal carbon dioxide homeostasis.

We have tested the hypothesis that interactions among eight parameters of the respiratory and cardiovascular systems that determine the loop gain (LG) of the respiratory CO2 feedback control system might account for the degree of stability or instability of breathing patterns in healthy sleeping volunteers as well as in familial dysautonomia (FD) and congenital central hypoventilation syndrome (CCHS) patients. The predictability of cycle duration was tested as well. We measured the values of CO2 sensitivity, CO2 delivery capacity in the circulation, circulation delay, mean lung volume for CO2, and mixed venous PCO2 in 8 FD patients, 2 CCHS patients, and 19 healthy controls. The values of these parameters were used in a mathematical model to compute the LG of the respiratory control system during sleep for each epoch of respiration analyzed. The strength of the ventilatory oscillations (R) was quantified using power density spectra of the ventilation time series. All subjects were studied at inspiratory O2 concentrations (FIO2) of 0.21 and 0.15; CCHS patients and controls were also studied at 0.12 FIO2 to examine the effect of steady-state hypoxia on respiratory system stability. In 2 FD patients, LG was elevated at both levels of FIO2 and periodic breathing was observed; the values of R were elevated. Elevated mixed venous PCO2 and reduced CO2 delivery capacity were chiefly responsible for the abnormally high LG observed. In three healthy volunteers, high LG and unstable patterns were associated with high chemosensitivity. The CCHS patients, however, remained stable even at 0.12 FIO2 because LG remained equivalent to zero due to a lack of chemosensitivity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Varenicline Effects on Smoking,Cognition, and Psychiatric Symptoms in Schizophrenia: A Double-Blind Randomized Trial

Schizophrenic patients have a high rate of smoking and cognitive deficits which may be related to a decreased number or responsiveness of nicotinic receptors in their brains. Varenicline is a partial nicotinic agonist which is effective as an antismoking drug in cigarette smokers, although concerns have been raised about potential psychiatric side-effects. We conducted a double-blind placebo controlled study in 87 schizophrenic smokers to evaluate the effects of varenicline (2 mg/day) on measures of smoking, cognition, psychiatric symptoms, and side-effects in schizophrenic patients who were cigarette smokers. Varenicline significantly decreased cotinine levels (P<0.001), and other objective and subjective measures of smoking (P < .01), and responses on a smoking urges scale (P = .02), more than placebo. Varenicline did not improve scores on a cognitive battery designed to test the effect of drugs on cognitive performance in schizophrenia (the MATRICS battery), either in overall MATRICS battery Composite or individual Domain scores, more than placebo. There were no significant differences between varenicline vs. placebo effects on total symptom scores on psychiatric rating scales, PANSS, SANS, or Calgary Depression scales, and there were no significant drug effects in any of these scales sub-scores when we used Benjamin-Hochberg corrected significance levels (α = .05). Varenicline patients did not show greater side-effects than placebo treated patients at any time point when controlled for baseline side-effect scores. Our study supports the use of varenicline as a safe drug for smoking reduction in schizophrenia but not as a cognitive enhancer.Trial Registration: ClinicalTrials.gov 00802919     

A Tetraploid Intermediate Precedes Aneuploid Formation in Yeasts Exposed to Fluconazole

Candida albicans, the most prevalent human fungal pathogen, is generally diploid. However, 50% of isolates that are resistant to fluconazole (FLC), the most widely used antifungal, are aneuploid and some aneuploidies can confer FLC resistance. To ask if FLC exposure causes or only selects for aneuploidy, we analyzed diploid strains during exposure to FLC using flow cytometry and epifluorescence microscopy. FLC exposure caused a consistent deviation from normal cell cycle regulation: nuclear and spindle cycles initiated prior to bud emergence, leading to “trimeras,” three connected cells composed of a mother, daughter, and granddaughter bud. Initially binucleate, trimeras underwent coordinated nuclear division yielding four daughter nuclei, two of which underwent mitotic collapse to form a tetraploid cell with extra spindle components. In subsequent cell cycles, the abnormal number of spindles resulted in unequal DNA segregation and viable aneuploid progeny. The process of aneuploid formation in C. albicans is highly reminiscent of early stages in human tumorigenesis in that aneuploidy arises through a tetraploid intermediate and subsequent unequal DNA segregation driven by multiple spindles coupled with a subsequent selective advantage conferred by at least some aneuploidies during growth under stress. Finally, trimera formation was detected in response to other azole antifungals, in related Candida species, and in an in vivo model for Candida infection, suggesting that aneuploids arise due to azole treatment of several pathogenic yeasts and that this can occur during the infection process.