Vision-related convergent gene losses reveal SERPINE3's unknown role in the eye.

Despite decades of research, knowledge about the genes that are important for development and function of the mammalian eye and are involved in human eye disorders remains incomplete. During mammalian evolution, mammals that naturally exhibit poor vision or regressive eye phenotypes have independently lost many eye-related genes. This provides an opportunity to predict novel eye-related genes based on specific evolutionary gene loss signatures. Building on these observations, we performed a genome-wide screen across 49 mammals for functionally uncharacterized genes that are preferentially lost in species exhibiting lower visual acuity values. The screen uncovered several genes, including SERPINE3, a putative serine proteinase inhibitor. A detailed investigation of 381 additional mammals revealed that SERPINE3 is independently lost in 18 lineages that typically do not primarily rely on vision, predicting a vision-related function for this gene. To test this, we show that SERPINE3 has the highest expression in eyes of zebrafish and mouse. In the zebrafish retina, serpine3 is expressed in Müller glia cells, a cell type essential for survival and maintenance of the retina. A CRISPR-mediated knockout of serpine3 in zebrafish resulted in alterations in eye shape and defects in retinal layering. Furthermore, two human polymorphisms that are in linkage with SERPINE3 are associated with eye-related traits. Together, these results suggest that SERPINE3 has a role in vertebrate eyes. More generally, by integrating comparative genomics with experiments in model organisms, we show that screens for specific phenotype-associated gene signatures can predict functions of uncharacterized genes.

AMPK activator O304 improves metabolic and cardiac function, and exercise capacity in aged mice.

Age is associated with progressively impaired, metabolic, cardiac and vascular function, as well as reduced work/exercise capacity, mobility, and hence quality of life. Exercise exhibit positive effects on age-related dysfunctions and diseases. However, for a variety of reasons many aged individuals are unable to engage in regular physical activity, making the development of pharmacological treatments that mimics the beneficial effects of exercise highly desirable. Here we show that the pan-AMPK activator O304, which is well tolerated in humans, prevented and reverted age-associated hyperinsulinemia and insulin resistance, and improved cardiac function and exercise capacity in aged mice. These results provide preclinical evidence that O304 mimics the beneficial effects of exercise. Thus, as an exercise mimetic in clinical development, AMPK activator O304 holds great potential to mitigate metabolic dysfunction, and to improve cardiac function and exercise capacity, and hence quality of life in aged individuals.

Identification of Signaling Pathways for Early Embryonic Lethality and Developmental Retardation in Sephs1-/- Mice.

Selenophosphate synthetase 1 (SEPHS1) plays an essential role in cell growth and survival. However, the underlying molecular mechanisms remain unclear. In the present study, the pathways regulated by SEPHS1 during gastrulation were determined by bioinformatical analyses and experimental verification using systemic knockout mice targeting Sephs1. We found that the coagulation system and retinoic acid signaling were most highly affected by SEPHS1 deficiency throughout gastrulation. Gene expression patterns of altered embryo morphogenesis and inhibition of Wnt signaling were predicted with high probability at E6.5. These predictions were verified by structural abnormalities in the dermal layer of Sephs1-/- embryos. At E7.5, organogenesis and activation of prolactin signaling were predicted to be affected by Sephs1 knockout. Delay of head fold formation was observed in the Sephs1-/- embryos. At E8.5, gene expression associated with organ development and insulin-like growth hormone signaling that regulates organ growth during development was altered. Consistent with these observations, various morphological abnormalities of organs and axial rotation failure were observed. We also found that the gene sets related to redox homeostasis and apoptosis were gradually enriched in a time-dependent manner until E8.5. However, DNA damage and apoptosis markers were detected only when the Sephs1-/- embryos aged to E9.5. Our results suggest that SEPHS1 deficiency causes a gradual increase of oxidative stress which changes signaling pathways during gastrulation, and afterwards leads to apoptosis.

Effect of Long-Term and Short-Term Imbalanced Zn Manipulation on Gut Microbiota and Screening for Microbial Markers Sensitive to Zinc Status.

Zinc (Zn) imbalance is a common single-nutrient disorder worldwide, but little is known about the short-term and long-term effects of imbalanced dietary zinc in the intestinal microbiome. Here, 3-week-old C57BL/6 mice were fed diets supplemented with Zn at the doses of 0 (low Zn), 30 (control Zn), 150 (high Zn), and 600 mg/kg of body weight (excess Zn) for 4 weeks (short term) and 8 weeks (long term). The gut bacterial composition at the phyla, genus, and species levels were changed as the result of the imbalanced Zn diet (e.g., Lactobacillus reuteri and Akkermansia muciniphila). Moreover, pathways including carbohydrate, glycan, and nucleotide metabolism were decreased by a short-term low-Zn diet. Valeriate production was suppressed by a long-term low-Zn diet. Pathways such as drug resistance and infectious diseases were upregulated in high- and excess-Zn diets over 4-week and 8-week intervals. Long-term zinc fortification doses, especially at the high-Zn level, suppressed the abundance of short-chain fatty acids (SCFAs)-producing genera as well as the concentrations of metabolites. Finally, Melainabacteria (phylum) and Desulfovibrio sp. strain ABHU2SB (species) were identified to be potential markers for Zn status with high accuracy (area under the curve [AUC], >0.8). Collectively, this study identified significant changes in gut microbial composition and its metabolite concentration in altered Zn-fed mice and the relevant microbial markers for Zn status. IMPORTANCE Zn insufficiency is an essential health problem in developing countries. To prevent the occurrence of zinc deficit, zinc fortification and supplementation are widely used. However, in developed countries, the amounts of Zn consumed often exceed the tolerable upper intake limit. Our results demonstrated that dietary Zn is an essential mediator of microbial community structure and that both Zn deficiency and Zn overdose can generate a dysbiosis in the gut microbiota. Moreover, specific microbial biomarkers of Zn status were identified and correlated with serum Zn level. Our study found that a short-term low-Zn diet (0 mg/kg) and a long-term high-zinc diet (150 mg/kg) had obvious negative effects in a mouse model. Thus, these results indicate that the provision and duration of supplemental Zn should be approached with caution.

Simplified murine multipotent progenitor isolation scheme: Establishing a consensus approach for multipotent progenitor identification.

The mouse hematopoietic system has served as a paradigm for analysis of developmental fate decisions in tissue homeostasis and regeneration. However, multiple immunophenotypic definitions of, and sometimes divergent nomenclatures used to classify, murine multipotent progenitors (MPPs) have emerged in the field over time. This has created significant confusion and inconsistency in the hematology field. To facilitate easier comparison of murine MPP phenotypes between research laboratories, a working group of four International Society for Experimental Hematology (ISEH) members with extensive experience studying the functional activities associated with different MPP phenotypic definitions reviewed the current state of the field with the goal of developing a position statement toward a simplified and unified immunophenotypic definition of MPP populations. In November of 2020, this position statement was presented as a webinar to the ISEH community for discussion and feedback. Hence, the Simplified MPP Identification Scheme presented here is the result of curation of existing literature, consultation with leaders in the field, and crowdsourcing from the wider experimental hematology community. Adoption of a unified definition and nomenclature, while still leaving room for individual investigator customization, will benefit scientists at all levels trying to compare these populations between experimental settings.

Similarities of developmental gene expression changes in the brain between human and experimental animals: rhesus monkey, mouse, Zebrafish, and Drosophila.

AIM: Experimental animals, such as non-human primates (NHPs), mice, Zebrafish, and Drosophila, are frequently employed as models to gain insights into human physiology and pathology. In developmental neuroscience and related research fields, information about the similarities of developmental gene expression patterns between animal models and humans is vital to choose what animal models to employ. Here, we aimed to statistically compare the similarities of developmental changes of gene expression patterns in the brains of humans with those of animal models frequently used in the neuroscience field. METHODS: The developmental gene expression datasets that we analyzed consist of the fold-changes and P values of gene expression in the brains of animals of various ages compared with those of the youngest postnatal animals available in the dataset. By employing the running Fisher algorithm in a bioinformatics platform, BaseSpace, we assessed similarities between the developmental changes of gene expression patterns in the human (Homo sapiens) hippocampus with those in the dentate gyrus (DG) of the rhesus monkey (Macaca mulatta), the DG of the mouse (Mus musculus), the whole brain of Zebrafish (Danio rerio), and the whole brain of Drosophila (D. melanogaster). RESULTS: Among all possible comparisons of different ages and animals in developmental changes in gene expression patterns within the datasets, those between rhesus monkeys and mice were highly similar to those of humans with significant overlap P-value as assessed by the running Fisher algorithm. There was the highest degree of gene expression similarity between 40-59-year-old humans and 6-12-year-old rhesus monkeys (overlap P-value = 2.1 × 10- 72). The gene expression similarity between 20-39-year-old humans and 29-day-old mice was also significant (overlap P = 1.1 × 10- 44). Moreover, there was a similarity in developmental changes of gene expression patterns between 1-2-year-old Zebrafish and 40-59-year-old humans (Overlap P-value = 1.4 × 10- 6). The overlap P-value of developmental gene expression patterns between Drosophila and humans failed to reach significance (30 days Drosophila and 6-11-year-old humans; overlap P-value = 0.0614). CONCLUSIONS: These results indicate that the developmental gene expression changes in the brains of the rhesus monkey, mouse, and Zebrafish recapitulate, to a certain degree, those in humans. Our findings support the idea that these animal models are a valid tool for investigating the development of the brain in neurophysiological and neuropsychiatric studies.

Mouse background genetics in biomedical research: The devil's in the details.

BACKGROUND: Genetically modified mice are used widely to explore mechanisms in most biomedical fields-including transfusion. Concluding that a gene modification is responsible for a phenotypic change assumes no other differences between the gene-modified and wild-type mice besides the targetted gene. STUDY DESIGN AND METHODS: To test the hypothesis that the N-terminus of Band3, which regulates metabolism, affects RBC storage biology, RBCs from mice with a modified N-terminus of Band3 were stored under simulated blood bank conditions. All strains of mice were generated with the same initial embryonic stem cells from 129 mice and each strain was backcrossed with C57BL/6 (B6) mice. Both 24-h recoveries post-transfusion and metabolomics were determined for stored RBCs. Genetic profiles of mice were assessed by a high-resolution SNP array. RESULTS: RBCs from mice with a mutated Band3 N-terminus had increased lipid oxidation and worse 24-h recoveries, "demonstrating" that Band3 regulates oxidative injury during RBC storage. However, SNP analysis demonstrated variable inheritance of 129 genetic elements between strains. Controlled interbreeding experiments demonstrated that the changes in lipid oxidation and some of the decreased 24-hr recovery were caused by inheritance of a region of chromosome 1 of 129 origin, and not due to the modification of Band 3. SNP genotyping of a panel of commonly used commercially available KO mice showed considerable 129 contamination, despite wild-type B6 mice being listed as the correct control. DISCUSSION: Thousands of articles published each year use gene-modified mice, yet genetic background issues are rarely considered. Assessment of such issues are not, but should become, routine norms of murine experimentation.

Spatial transcriptomics analysis of uterine gene expression in enhancer of zeste homolog 2 conditional knockout mice†.

Histone proteins undergo various modifications that alter chromatin structure, including addition of methyl groups. Enhancer of zeste homolog 2 (EZH2) is a histone methyltransferase that methylates lysine residue 27, and thereby suppresses gene expression. EZH2 plays integral roles in the uterus and other reproductive organs. We have previously shown that conditional deletion of uterine EZH2 results in increased proliferation of luminal and glandular epithelial cells, and RNA-seq analyses reveal several uterine transcriptomic changes in Ezh2 conditional (c) knockout (KO) mice that can affect estrogen signaling pathways. To pinpoint the origin of such gene expression changes, we used the recently developed spatial transcriptomics (ST) method with the hypotheses that Ezh2cKO mice would predominantly demonstrate changes in epithelial cells and/or ablation of this gene would disrupt normal epithelial/stromal gene expression patterns. Uteri were collected from ovariectomized adult WT and Ezh2cKO mice and analyzed by ST. Asb4, Cxcl14, Dio2, and Igfbp5 were increased, Sult1d1, Mt3, and Lcn2 were reduced in Ezh2cKO uterine epithelium vs. WT epithelium. For Ezh2cKO uterine stroma, differentially expressed key hub genes included Cald1, Fbln1, Myh11, Acta2, and Tagln. Conditional loss of uterine Ezh2 also appears to shift the balance of gene expression profiles in epithelial vs. stromal tissue toward uterine epithelial cell and gland development and proliferation, consistent with uterine gland hyperplasia in these mice. Current findings provide further insight into how EZH2 may selectively affect uterine epithelial and stromal compartments. Additionally, these transcriptome data might provide mechanistic understanding and valuable biomarkers for human endometrial disorders with epigenetic underpinnings.

Vaginal mucus in mice: developmental and gene expression features of epithelial mucous cells during pregnancy†.

The vagina is the site of copulation and serves as the birth canal. It also provides protection against external pathogens. In mice, due to the absence of cervical glands, the vaginal epithelium is the main producer of vaginal mucus. The development and differentiation of vaginal epithelium-constituting cells and the molecular characteristics of vaginal mucus have not been thoroughly examined. Here, we characterized vaginal mucous cell development and the expression of mucus-related factors in pregnant mice. The vaginal mucous epithelium layer thickened and became multilayered after Day 12 of pregnancy and secreted increasing amounts of mucus until early postpartum. Using histochemistry and transmission electron microscopy, we found supra-basal mucous cells as probable candidates for precursor cells. In vaginal mucous cells, the expression of TFF1, a stabilizer of mucus, was high, and some members of mucins and antimicrobial peptides (MUC5B and DEFB1) were expressed in a stage-dependent manner. In summary, this study presents the partial characterization of vaginal epithelial mucous cell lineage and expression of genes encoding several peptide substances that may affect vaginal tissue homeostasis and mucosal immunity during pregnancy and parturition.

CD34 protein is expressed in murine, canine, and porcine lungs.

The cell surface protein CD34 is expressed in various human tissues and cells, including hematopoietic stem cells, vascular endothelial cells, mucosal dendritic cells, mast cells, eosinophils, microglia, fibrocytes, muscle satellite cells, and platelets. There is a lack of data on the expression of CD34 in canine and porcine tissues. Therefore, we designed a series of immunoblotting, immunohistochemistry, and immunofluorescence experiments to observe CD34 expression in murine, canine, and porcine lungs. We used a rabbit antibody (clone EP373Y) to target the conserved human CD34 C-terminal region and validated its immunoreactivity against mouse lung homogenates. The data showed diffuse bronchiolar and alveolar epithelial localization of CD34 protein in normal murine, canine, and porcine lungs. At 9 or 24 h after bacterial endotoxin exposure, murine CD34 protein shifted to specific bronchoalveolar cells with a punctate pattern, as quantified by CD34 fluorescence. Specific porcine bronchoalveolar cells and leukocytes had significant CD34-positive immunostaining after H3N1 influenza infection. Thus, our study provides fundamental data on the expression of CD34 in lungs and validates an antibody for use in further experiments in these animal species.

La protéine de surface cellulaire CD34 est exprimée dans divers tissus et cellules humains, y compris les cellules souches hématopoïétiques, les cellules endothéliales vasculaires, les cellules dendritiques des muqueuses, les mastocytes, les éosinophiles, la microglie, les fibrocytes, les cellules satellites musculaires et les plaquettes. Il existe un manque de données sur l'expression de CD34 dans les tissus canins et porcins. Par conséquent, nous avons conçu une série d'expériences d'immunobuvardage, d'immunohistochimie et d'immunofluorescence pour observer l'expression de CD34 dans les poumons murins, canins et porcins. Nous avons utilisé un anticorps de lapin (clone EP373Y) pour cibler la région C-terminale conservée du CD34 humain et validé son immunoréactivité contre des homogénats pulmonaires de souris. Les données ont montré une localisation épithéliale bronchiolaire et alvéolaire diffuse de la protéine CD34 dans les poumons normaux murins, canins et porcins. À 9 ou 24 h après l'exposition à l'endotoxine bactérienne, la protéine CD34 murine s'est déplacée vers des cellules bronchoalvéolaires spécifiques avec un motif ponctué, tel que quantifié par la fluorescence envers CD34. Des cellules bronchoalvéolaires et des leucocytes porcins spécifiques présentaient une immunocoloration significativement positive pour CD34 après une infection par le virus de l'influenza H3N1. Ainsi, notre étude fournit des données fondamentales sur l'expression de CD34 dans les poumons et valide un anticorps à utiliser dans d'autres expériences chez ces espèces animales.(Traduit par Docteur Serge Messier).

14-3-3-protein regulates Nedd4-2 by modulating interactions between HECT and WW domains.

Neural precursor cell expressed developmentally down-regulated 4 ligase (Nedd4-2) is an E3 ubiquitin ligase that targets proteins for ubiquitination and endocytosis, thereby regulating numerous ion channels, membrane receptors and tumor suppressors. Nedd4-2 activity is regulated by autoinhibition, calcium binding, oxidative stress, substrate binding, phosphorylation and 14-3-3 protein binding. However, the structural basis of 14-3-3-mediated Nedd4-2 regulation remains poorly understood. Here, we combined several techniques of integrative structural biology to characterize Nedd4-2 and its complex with 14-3-3. We demonstrate that phosphorylated Ser342 and Ser448 are the key residues that facilitate 14-3-3 protein binding to Nedd4-2 and that 14-3-3 protein binding induces a structural rearrangement of Nedd4-2 by inhibiting interactions between its structured domains. Overall, our findings provide the structural glimpse into the 14-3-3-mediated Nedd4-2 regulation and highlight the potential of the Nedd4-2:14-3-3 complex as a pharmacological target for Nedd4-2-associated diseases such as hypertension, epilepsy, kidney disease and cancer.

The outer membrane protein Amuc_1100 of Akkermansia muciniphila alleviates the depression-like behavior of depressed mice induced by chronic stress.

Akkermansia muciniphila is a symbiotic intestinal bacterium with a high medicinal value. Amuc_1100 is the outer membrane protein of A. muciniphila and plays an important role in the interaction between A. muciniphila and its host. The objective of this study was to evaluate the antidepressant activity of Amuc_1100 in a chronic unpredictable mild stress (CUMS) model. Amuc_1100 intervention ameliorated CUMS-induced depression-like behavior and CUMS-induced down-regulation of serotonin (5-hydroxytryptamine, or simply, 5-HT) in the serum and colon of mice. Microbial analysis of mouse feces showed that Amuc_1100 could improve the gut microbiota dysregulation induced by CUMS. In addition, Amuc_1100 intervention could also improve the down-regulation of brain-derived neurotrophic factor (BDNF) and inflammation in the hippocampus induced by CUMS. These results suggest that Amuc_1100 has a good antidepressant effect, and the mechanism may be related to the improvement of gut microbiota, the up-regulation of the BDNF level, and the inhibition of the neuroinflammatory response.

Testicular localization of activating transcription factor 1 and its potential function during spermatogenesis†.

Activating transcription factor 1 (ATF1), belonging to the CREB/ATF family of transcription factors, is highly expressed in the testes. However, its role in spermatogenesis has not yet been established. Here, we aimed to elucidate the impact of ATF1 in spermatogenesis by examining the expression pattern of ATF1 in mice and the effect of ATF1 knockdown in the mouse testes. We found that ATF1 is expressed in various organs, with very high levels in the testes. Immunohistochemical staining showed that ATF1 was localized in the nuclei of spermatogonia and co-localized with proliferating cell nuclear antigen. In ATF1-deficient mice, the seminiferous tubules of the testis contained cells at all developmental stages; however, the number of spermatocytes was decreased. Proliferating cell nuclear antigen expression was decreased and apoptotic cells were rare in the seminiferous tubules. These results indicate that ATF1 plays a role in male germ cell proliferation and sperm production.

Urinary protein analysis in mice lacking major urinary proteins.

Mouse urine contains major urinary proteins (MUPs) that are not found in human urine. Therefore, even healthy mice exhibit proteinuria, unlike healthy humans, making it challenging to use mice as models for human diseases. It was also unknown whether dipsticks for urinalysis could measure protein concentrations precisely in urine containing MUPs. To resolve these problems, we produced MUP-knockout (Mup-KO) mice by removing the Mup gene cluster using Cas9 proteins and two guide RNAs and characterized the urinary proteins in these mice. We measured the urinary protein concentrations in Mup-KO and wild-type mice using a protein quantitation kit and dipsticks. We also examined the urinary protein composition using SDS-PAGE and two-dimensional electrophoresis (2DE). The urinary protein concentration was significantly lower (P<0.001) in Mup-KO mice (17.9 ± 1.8 mg/dl, mean ± SD, n=3) than in wild-type mice (73.7 ± 8.2 mg/dl, n=3). This difference was not reflected in the dipstick values, perhaps due to the low sensitivity to MUPs. This suggests that dipsticks have limited ability to measure changes in MUPs with precision. SDS-PAGE and 2DE confirmed that Mup-KO mice, like humans, had no MUPs in their urine, whereas wild-type mice had abundant MUPs in their urine. The absence of the masking effect of MUPs in 2DE would enable clear comparisons of urinary proteins, especially low-molecular-weight proteins. Thus, Mup-KO mice may provide a useful model for human urinalysis.

The transcription factor Rreb1 regulates epithelial architecture, invasiveness, and vasculogenesis in early mouse embryos.

Ras-responsive element-binding protein 1 (Rreb1) is a zinc-finger transcription factor acting downstream of RAS signaling. Rreb1 has been implicated in cancer and Noonan-like RASopathies. However, little is known about its role in mammalian non-disease states. Here, we show that Rreb1 is essential for mouse embryonic development. Loss of Rreb1 led to a reduction in the expression of vasculogenic factors, cardiovascular defects, and embryonic lethality. During gastrulation, the absence of Rreb1 also resulted in the upregulation of cytoskeleton-associated genes, a change in the organization of F-ACTIN and adherens junctions within the pluripotent epiblast, and perturbed epithelial architecture. Moreover, Rreb1 mutant cells ectopically exited the epiblast epithelium through the underlying basement membrane, paralleling cell behaviors observed during metastasis. Thus, disentangling the function of Rreb1 in development should shed light on its role in cancer and other diseases involving loss of epithelial integrity.

Generation of a mouse SWATH-MS spectral library to quantify 10148 proteins involved in cell reprogramming.

Murine models are amongst the most widely used systems to study biology and pathology. Targeted quantitative proteomic analysis is a relatively new tool to interrogate such systems. Recently the need for relative quantification on hundreds to thousands of samples has driven the development of Data Independent Acquisition methods. One such technique is SWATH-MS, which in the main requires prior acquisition of mass spectra to generate an assay reference library. In stem cell research, it has been shown pluripotency can be induced starting with a fibroblast population. In so doing major changes in expressed proteins is inevitable. Here we have created a reference library to underpin such studies. This is inclusive of an extensively documented script to enable replication of library generation from the raw data. The documented script facilitates reuse of data and adaptation of the library to novel applications. The resulting library provides deep coverage of the mouse proteome. The library covers 29519 proteins (53% of the proteome) of which 7435 (13%) are supported by a proteotypic peptide.

Redundant and non-redundant cytokine-activated enhancers control Csn1s2b expression in the lactating mouse mammary gland.

Enhancers are transcription factor platforms that synergize with promoters to control gene expression. Here, we investigate enhancers that activate gene expression several hundred-fold exclusively in the lactating mouse mammary gland. Using ChIP-seq for activating histone marks and transcription factors, we identify two candidate enhancers and one super-enhancer in the Csn1s2b locus. Through experimental mouse genetics, we dissect the lactation-specific distal enhancer bound by the mammary-enriched transcription factors STAT5 and NFIB and the glucocorticoid receptor. While deletions of canonical binding motifs for NFIB and STAT5, individually or combined, have a limited biological impact, a non-canonical STAT5 site is essential for enhancer activity during lactation. In contrast, the intronic enhancer contributes to gene expression only in late pregnancy and early lactation, possibly by interacting with the distal enhancer. A downstream super-enhancer, which physically interacts with the distal enhancer, is required for the functional establishment of the Csn1s2b promoter and gene activation. Lastly, NFIB binding in the promoter region fine-tunes Csn1s2b expression. Our study provides comprehensive insight into the anatomy and biology of regulatory elements that employ the JAK/STAT signaling pathway and preferentially activate gene expression during lactation.

Dietary protein content and digestibility influences discrimination of amino acid nitrogen isotope values in a terrestrial omnivorous mammal.

RATIONALE: Ecologists increasingly determine the δ15 N values of amino acids (AA) in animal tissue; "source" AA typically exhibit minor variation between diet and consumer, while "trophic" AA have increased δ15 N values in consumers. Thus, trophic-source δ15 N offsets (i.e., Δ15 NT-S ) reflect trophic position in a food web. However, even minor variations in δ15 Nsource AA values may influence the magnitude of offset that represents a trophic step, known as the trophic discrimination factor (i.e., TDFT-S ). Diet digestibility and protein content can influence the δ15 N values of bulk animal tissue, but the effects of these factors on AA Δ15 NT-S and TDFT-S in mammals are unknown. METHODS: We fed captive mice (Mus musculus) either (A) a low-fat, high-fiber diet with low, intermediate, or high protein; or (B) a high-fat, low-fiber diet with low or intermediate protein. Mouse muscle and dietary protein were analyzed for bulk tissue δ15 N using elemental analyzer-isotope ratio mass spectrometry (EA-IRMS), and were also hydrolyzed into free AA that were analyzed for δ15 N using gas chromatography-combustion-IRMS. RESULTS: As dietary protein increased, Δ15 NConsumer-Diet slightly declined for bulk muscle tissue in both experiments; increased for AA in the low-fat, high-fiber diet (A); and remained the same or decreased for AA in the high-fat, low-fiber diet (B). The effects of dietary protein on Δ15 NT-S and on TDFT-S varied by AA but were consistent between variables. CONCLUSIONS: Diets were less digestible and included more protein in Experiment A than in Experiment B. As a result, the mice in Experiment A probably oxidized more AA, resulting in greater Δ15 NConsumer-Diet values. However, the similar responses of Δ15 NT-S and of TDFT-S to diet variation suggest that if diet samples are available, Δ15 NT-S accurately tracks trophic position. If diet samples are not available, the patterns presented here provide a basis to interpret Δ15 NT-S values. The trophic-source offset of Pro-Lys did not vary across diets, and therefore may be more reliable for omnivores than other offsets (e.g., Glu-Phe).

First record on mercury accumulation in mice brain living in active volcanic environments: a cytochemical approach.

The health effects of mercury vapor exposure on the brain in volcanic areas have not been previously addressed in the literature. However, 10% of the worldwide population inhabits in the vicinity of an active volcano, which are natural sources of elemental mercury emission. To evaluate the presence of mercury compounds in the brain after chronic exposure to volcanogenic mercury vapor, a histochemical study, using autometallographic silver, was carried out to compare the brain of mice chronically exposed to an active volcanic environment (Furnas village, Azores, Portugal) with those not exposed (Rabo de Peixe village, Azores, Portugal). Results demonstrated several mercury deposits in blood vessels, white matter and some cells of the hippocampus in the brain of chronically exposed mice. Our results highlight that chronic exposure to an active volcanic environment results in brain mercury accumulation, raising an alert regarding potential human health risks. These findings support the hypothesis that mercury exposure can be a risk factor in causing neurodegenerative diseases in the inhabitants of volcanically active areas.