Zinc-stimulated endocytosis controls activity of the mouse ZIP1 and ZIP3 zinc uptake transporters

The mouse mZip1 and mZip3 zinc transporters have been implicated in zinc acquisition by the cells of many tissues. This hypothesis raised the question of whether activity of these proteins is regulated to maintain zinc homeostasis. Neither mZIP1 nor mZIP3 mRNA levels are highly regulated by zinc status. Therefore, we investigated whether zinc controls the activity of these proteins post-translationally by altering their subcellular distribution. When expressed in transfected cells grown in zinc-replete medium, both mZip1 and mZip3 were largely present in intracellular organelles. However, these proteins were found to rapidly transit between the plasma membrane and intracellular compartments in zinc-replete cells. Zinc deficiency increased plasma membrane levels of mZip1 and mZip3 by decreasing their rates of endocytosis. Greater zinc deficiency was required to alter mZip3 distribution than was needed to affect mZip1. Increased surface levels correlated with increased zinc uptake activity. Taken together, these results suggest that post-translational control of mZip1 and mZip3 localization plays a role in zinc homeostasis. Moreover, our results indicate that zinc-responsive endocytosis is a conserved mechanism controlling activity of many mammalian zinc uptake transporters.     

The acrodermatitis enteropathica gene ZIP4 encodes a tissue-specific,zinc-regulated zinc transporter in mice

The human ZIP4 gene (SLC39A4) is a candidate for the genetic disorder of zinc metabolism acrodermatitis enteropathica. To understand its role in zinc homeostasis, we examined the function and expression of mouse ZIP4. This gene encodes a well conserved eight-transmembrane protein that can specifically increase the influx of zinc into transfected cells. Expression of this gene is robust in tissues involved in nutrient uptake, such as the intestines and embryonic visceral yolk sac, and is dynamically regulated by zinc. Dietary zinc deficiency causes a marked increase in the accumulation of ZIP4 mRNA in these tissues, whereas injection of zinc or increasing zinc content of the diet rapidly reduces its abundance. Zinc can also regulate the accumulation of ZIP4 protein at the apical surface of enterocytes and visceral endoderm cells. These results provide compelling evidence that ZIP4 is a zinc transporter that plays an important role in zinc homeostasis, a process that is defective in acrodermatitis enteropathica in humans.     

Incision at hypoxanthine residues in DNA by a mammalian homologue of the Escherichia coli antimutator enzyme endonuclease V

Deamination of DNA bases can occur spontaneously, generating highly mutagenic lesions such as uracil and hypoxanthine. In Escherichia coli two enzymes initiate repair at hypoxanthine residues in DNA. The alkylbase DNA glycosylase, AlkA, initiates repair by removal of the damaged base, whereas endonuclease V, Endo V, hydrolyses the second phosphodiester bond 3′ to the lesion. We have identified and characterised a mouse cDNA with striking homology to the E.coli nfi gene, which also has significant similarities to motifs required for catalytic activity of the UvrC endonuclease. The 37-kDa mouse enzyme (mEndo V) incises the DNA strand at the second phosphodiester bond 3′ to hypoxanthine- and uracil-containing nucleotides. The activity of mEndo V is elevated on single-stranded DNA substrate in vitro. Expression of the mouse protein in a DNA repair-deficient E.coli alkA nfi strain suppresses its spontaneous mutator phenotype. We suggest that mEndo V initiates an alternative excision repair pathway for hypoxanthine removal. It thus appears that mEndo V has properties overlapping the function of alkylbase DNA glycosylase (Aag) in repair of deaminated adenine, which to some extent could explain the absence of phenotypic abnormalities associated with Aag knockout in mice.     

The GEF1 gene of Saccharomyces cerevisiae encodes an integral membrane protein; mutations in which have effects on respiration and iron-limited growth

We have isolated a new class of respiration-defective, i.e petite, mutants of the yeast Saccharomyces cerevisiae. Mutations in the GEF1 gene cause cells to grow slowly on rich media containing carbon sources utilized by respiration. This phenotype is suppressed by adding high concentrations of iron to the growth medium. Gef1 ^– mutants also fail to grow on a fermentable carbon source, glucose, when iron is reduced to low concentrations in the medium, suggesting that the GEF1 gene is required for efficient metabolism of iron during growth on fermentable as well as respired carbon sources. However, activity of the iron uptake system appears to be unaffected in gef1 ^– mutants. Fe(II) transporter activity and regulation is normal in gef1 ^– mutants. Fe(III) reductase induction during iron-limited growth is disrupted, but this appears to be a secondary effect of growth rate alterations. The wild-type GEF1 gene was cloned and sequenced; it encodes a protein of 779 amino acids, 13 possible transmembrane domains, and significant similarity to chloride channel proteins from fish and mammals, suggesting that GEF1 encodes an integral membrane protein. A gef1 ^– deletion mutation generated in vitro and introduced into wild-type haploid strains by gene transplacement was not lethal. Oxygen consumption by intact gef1 ^– cells and by mitochondrial fractions isolated from gef1 ^– mutants was reduced 25–50% relative to wild type, indicating that mitochondrial function is defective in these mutants. We suggest that GEF1 encodes a transport protein that is involved in intracellular iron metabolism.     

Culture of adult mouse neurons

Primary neuronal cells used to model physiology are generally limited to embryonic tissue. However, embryonic tissue is not optimal as a model for age-related changes in physiology or late-onset disease. Successful culturing of neurons from adult animals, however, has been historically difficult, if not impossible. Here, we report methodology for routine and reliable cultivation of healthy striatal neurons from adult mice. The new methodology is cost-effective and improves the speed and simplicity of neuronal isolation.     

Maternal and Neonatal Mortality in South-West Ethiopia: Estimates and Socio-Economic Inequality

Introduction

Ethiopia has achieved the fourth Millennium Development Goal by reducing under 5 mortality. Nevertheless, there are challenges in reducing maternal and neonatal mortality. The aim of this study was to estimate maternal and neonatal mortality and the socio-economic inequalities of these mortalities in rural south-west Ethiopia.

Methods

We visited and enumerated all households but collected data from those that reported pregnancy and birth outcomes in the last five years in 15 of the 30 rural kebeles in Bonke woreda, Gamo Gofa, south-west Ethiopia. The primary outcomes were maternal and neonatal mortality and a secondary outcome was the rate of institutional delivery.

Results

We found 11,762 births in 6572 households; 11,536 live and 226 stillbirths. There were 49 maternal deaths; yielding a maternal mortality ratio of 425 per 100,000 live births (95% CI:318–556). The poorest households had greater MMR compared to richest (550 vs 239 per 100,000 live births). However, the socio-economic factors examined did not have statistically significant association with maternal mortality. There were 308 neonatal deaths; resulting in a neonatal mortality ratio of 27 per 1000 live births (95% CI: 24–30). Neonatal mortality was greater in households in the poorest quartile compared to the richest; adjusted OR (AOR): 2.62 (95% CI: 1.65–4.15), headed by illiterates compared to better educated; AOR: 3.54 (95% CI: 1.11–11.30), far from road (≥6 km) compared to within 5 km; AOR: 2.40 (95% CI: 1.56–3.69), that had three or more births in five years compared to two or less; AOR: 3.22 (95% CI: 2.45–4.22). Households with maternal mortality had an increased risk of stillbirths; OR: 11.6 (95% CI: 6.00–22.7), and neonatal deaths; OR: 7.2 (95% CI: 3.6–14.3). Institutional delivery was only 3.7%.

Conclusion

High mortality with socio-economic inequality and low institutional delivery highlight the importance of strengthening obstetric interventions in rural south-west Ethiopia.     

The oxidative stress of zinc deficiency

Zinc is an essential catalytic and structural cofactor for many enzymes and other proteins. While Zn2+ is not redox active under physiological conditions, it has been known for many years that zinc deficiency causes increased oxidative stress and, consequently, increased oxidative damage to DNA, proteins, and lipids. These results have indicated that zinc plays an indirect antioxidant role and that dietary inadequacy may contribute to human diseases such as cancer. Recent studies are helping to identify the primary sources of oxidative stress in low zinc. In addition, through studies of the model eukaryotic cell, Saccharomyces cerevisiae, we are now beginning to understand the strategies cells use to limit this stress and reduce its damage.