A tale of two toxicities: malformed selenoproteins and oxidative stress both contribute to selenium stress in plants

Background

Despite selenium''s toxicity in plants at higher levels, crops supply most of the essential dietary selenium in humans. In plants, inorganic selenium can be assimilated into selenocysteine, which can replace cysteine in proteins. Selenium toxicity in plants has been attributed to the formation of non-specific selenoproteins. However, this paradigm can be challenged now that there is increasingly abundant evidence suggesting that selenium-induced oxidative stress also contributes to toxicity in plants.

Scope

This Botanical Briefing summarizes the evidence indicating that selenium toxicity in plants is attributable to both the accumulation of non-specific selenoproteins and selenium-induced oxidative stress. Evidence is also presented to substantiate the claim that inadvertent selenocysteine replacement probably impairs or misfolds proteins, which supports the malformed selenoprotein hypothesis. The possible physiological ramifications of selenoproteins and selenium-induced oxidative stress are discussed.

Conclusions

Malformed selenoproteins and oxidative stress are two distinct types of stress that drive selenium toxicity in plants and could impact cellular processes in plants that have yet to be thoroughly explored. Although challenging, deciphering whether the extent of selenium toxicity in plants is imparted by selenoproteins or oxidative stress could be helpful in the development of crops with fortified levels of selenium.     

A calcaneus attributable to the primitive late eocene anthropoid Proteopithecus sylviae: Phenetic affinities and phylogenetic implications

A well‐preserved calcaneus referrable to Proteopithecus sylviae from the late Eocene Quarry L‐41 in the Fayum Depression, Egypt, provides new evidence relevant to this taxon's uncertain phylogenetic position. We assess morphological affinities of the new specimen using three‐dimensional geometric morphometric analyses with a comparative sample of primate calcanei representing major extinct and extant radiations (n = 58 genera, 106 specimens). Our analyses reveal that the calcaneal morphology of Proteopithecus is most similar to that of the younger Fayum parapithecid Apidium. Principal components analysis places Apidium and Proteopithecus in an intermediate position between primitive euprimates and crown anthropoids, based primarily on landmark configurations corresponding to moderate distal elongation, a more distal position of the peroneal tubercle, and a relatively “unflexed” calcaneal body. Proteopithecus and Apidium are similar to cercopithecoids and some omomyiforms in having an ectal facet that is more tightly curved, along with a larger degree of proximal calcaneal elongation, whereas other Fayum anthropoids, platyrrhines and adapiforms have a more open facet with less proximal elongation. The similarity to cercopithecoids is most plausibly interpreted as convergence given the less tightly curved ectal facets of stem catarrhines. The primary similarities between Proteopithecus and platyrrhines are mainly in the moderate distal elongation and the more distal position of the peroneal tubercle, both of which are not unique to these groups. Proteopithecus and Apidium exhibit derived anthropoid features, but also a suite of primitive retentions. The calcaneal morphology of Proteopithecus is consistent with our cladistic analysis, which places proteopithecids as a sister group of Parapithecoidea. Am J Phys Anthropol 151:372–397, 2013.© 2013 Wiley Periodicals, Inc.     

Extent and Degree of Shoreline Oiling: Deepwater Horizon Oil Spill,Gulf of Mexico,USA

The oil from the 2010 Deepwater Horizon spill in the Gulf of Mexico was documented by shoreline assessment teams as stranding on 1,773 km of shoreline. Beaches comprised 50.8%, marshes 44.9%, and other shoreline types 4.3% of the oiled shoreline. Shoreline cleanup activities were authorized on 660 km, or 73.3% of oiled beaches and up to 71 km, or 8.9% of oiled marshes and associated habitats. One year after the spill began, oil remained on 847 km; two years later, oil remained on 687 km, though at much lesser degrees of oiling. For example, shorelines characterized as heavily oiled went from a maximum of 360 km, to 22.4 km one year later, and to 6.4 km two years later. Shoreline cleanup has been conducted to meet habitat-specific cleanup endpoints and will continue until all oiled shoreline segments meet endpoints. The entire shoreline cleanup program has been managed under the Shoreline Cleanup Assessment Technique (SCAT) Program, which is a systematic, objective, and inclusive process to collect data on shoreline oiling conditions and support decision making on appropriate cleanup methods and endpoints. It was a particularly valuable and effective process during such a complex spill.     

Desynchronization of Theta-Phase Gamma-Amplitude Coupling during a Mental Arithmetic Task in Children with Attention Deficit/Hyperactivity Disorder

Introduction

Theta-phase gamma-amplitude coupling (TGC) measurement has recently received attention as a feasible method of assessing brain functions such as neuronal interactions. The purpose of this electroencephalographic (EEG) study is to understand the mechanisms underlying the deficits in attentional control in children with attention deficit/hyperactivity disorder (ADHD) by comparing the power spectra and TGC at rest and during a mental arithmetic task.

Methods

Nineteen-channel EEGs were recorded from 97 volunteers (including 53 subjects with ADHD) from a camp for hyperactive children under two conditions (rest and task performance). The EEG power spectra and the TGC data were analyzed. Correlation analyses between the Intermediate Visual and Auditory (IVA) continuous performance test (CPT) scores and EEG parameters were performed.

Results

No significant difference in the power spectra was detected between the groups at rest and during task performance. However, TGC was reduced during the arithmetic task in the ADHD group compared with the normal group (F = 16.70, p < 0.001). The TGC values positively correlated with the IVA CPT scores but negatively correlated with theta power.

Conclusions

Our findings suggest that desynchronization of TGC occurred during the arithmetic task in ADHD children. TGC in ADHD children is expected to serve as a promising neurophysiological marker of network deactivation during attention-demanding tasks.     

Microbiome Composition and Function Drives Wound-Healing Impairment in the Female Genital Tract

The mechanism(s) by which bacterial communities impact susceptibility to infectious diseases, such as HIV, and maintain female genital tract (FGT) health are poorly understood. Evaluation of FGT bacteria has predominantly been limited to studies of species abundance, but not bacterial function. We therefore sought to examine the relationship of bacterial community composition and function with mucosal epithelial barrier health in the context of bacterial vaginosis (BV) using metaproteomic, metagenomic, and in vitro approaches. We found highly diverse bacterial communities dominated by Gardnerella vaginalis associated with host epithelial barrier disruption and enhanced immune activation, and low diversity communities dominated by Lactobacillus species that associated with lower Nugent scores, reduced pH, and expression of host mucosal proteins important for maintaining epithelial integrity. Importantly, proteomic signatures of disrupted epithelial integrity associated with G. vaginalis-dominated communities in the absence of clinical BV diagnosis. Because traditional clinical assessments did not capture this, it likely represents a larger underrepresented phenomenon in populations with high prevalence of G. vaginalis. We finally demonstrated that soluble products derived from G. vaginalis inhibited wound healing, while those derived from L. iners did not, providing insight into functional mechanisms by which FGT bacterial communities affect epithelial barrier integrity.     

Mitochondrial oxidative stress causes hyperphosphorylation of tau

Age-related neurodegenerative disease has been mechanistically linked with mitochondrial dysfunction via damage from reactive oxygen species produced within the cell. We determined whether increased mitochondrial oxidative stress could modulate or regulate two of the key neurochemical hallmarks of Alzheimer's disease (AD): tau phosphorylation, and beta-amyloid deposition. Mice lacking superoxide dismutase 2 (SOD2) die within the first week of life, and develop a complex heterogeneous phenotype arising from mitochondrial dysfunction and oxidative stress. Treatment of these mice with catalytic antioxidants increases their lifespan and rescues the peripheral phenotypes, while uncovering central nervous system pathology. We examined sod2 null mice differentially treated with high and low doses of a catalytic antioxidant and observed striking elevations in the levels of tau phosphorylation (at Ser-396 and other phospho-epitopes of tau) in the low-dose antioxidant treated mice at AD-associated residues. This hyperphosphorylation of tau was prevented with an increased dose of the antioxidant, previously reported to be sufficient to prevent neuropathology. We then genetically combined a well-characterized mouse model of AD (Tg2576) with heterozygous sod2 knockout mice to study the interactions between mitochondrial oxidative stress and cerebral Ass load. We found that mitochondrial SOD2 deficiency exacerbates amyloid burden and significantly reduces metal levels in the brain, while increasing levels of Ser-396 phosphorylated tau. These findings mechanistically link mitochondrial oxidative stress with the pathological features of AD.     

Analysis of mouse skin reveals proteins that are altered in a diet-induced diabetic state: a new method for detection of type 2 diabetes

In this study, proteomic analysis was performed on the skin of C57BL/6J mice with type 2 diabetes and compared to nondiabetic controls. To induce obesity and subsequent diabetes, mice were placed on a high-fat diet for 16 wk. After 16 wk, both diabetic and nondiabetic control mice were sacrificed and their skin removed for analysis. Following 2-DE, proteomic profiles from the skin samples were quantified using PDQuest software. Out of more than 1000 distinct protein spots, 28 were shown to be significantly altered with 6 being decreased and 22 increased in the diabetic state compared to controls. The 28 protein spots were removed from the gels and analyzed by MALDI-TOF and MS/MS analyses. Protein identifications revealed that 17 of the 28 proteins were involved in energy metabolism (60.7% of changes observed). Collectively, none of the significantly altered proteins had been shown previously to be altered in diabetic skin. This study not only helps to identify proteins found in skin samples of obese mice with type 2 diabetes, but also shows that skin biopsies coupled with proteomic analysis may be useful as a noninvasive method for the diagnosis of hyperinsulinemia and diabetes.