Short-lived mammals (shrew, mouse) have a less robust metal-responsive transcription factor than humans and bats.

Non-essential "heavy" metals such as cadmium tend to accumulate in an organism and thus are a particular threat for long-lived animals. Here we show that two unrelated, short-lived groups of mammals (rodents and shrews, separated by 100 Mio years of evolution) each have independently acquired mutations in their metal-responsive transcription factor (MTF-1) in a domain relevant for robust transcriptional induction by zinc and cadmium. While key amino acids are mutated in rodents, in shrews an entire exon is skipped. Rodents and especially shrews are unique regarding the alterations of this region. To investigate the biological relevance of these alterations, MTF-1s from the common shrew (Sorex araneus), the mouse, humans and a bat (Myotis blythii), were tested by cotransfection with a reporter gene into cells lacking MTF-1. Whereas shrews only live for 1.5-2.5 years, bats, although living on a very similar insect diet, have a lifespan of several decades. We find that bat MTF-1 is similarly metal-responsive as its human counterpart, while shrew MTF-1 is less responsive, similar to mouse MTF-1. We propose that in comparison to most other mammals, the short-lived shrews and rodents can afford a "lower-quality" system for heavy metal homeostasis and detoxification.

The legless lizard Anguis fragilis (slow worm) has a potent metal-responsive transcription factor 1 (MTF-1).

The metal-responsive transcription factor-1 (MTF-1) is a key regulator of heavy metal homeostasis and detoxification. Here we characterize the first MTF-1 from a reptile, the slow worm Anguis fragilis. The slow worm, or blind worm, is a legless lizard also known for its long lifespan of up to several decades. Anguis MTF-1 performs well and matches the strong zinc and cadmium response of its human ortholog, clearly surpassing the activity of rodent MTF-1s. Some amino acid positions critical for metal response are the same in humans and slow worm but not in rodent MTF-1. This points to a divergent evolution of rodent MTF-1, and we speculate that rodents can afford a less sophisticated metal handling than humans and (some) reptiles.

The Drosophila copper transporter Ctr1C functions in male fertility.

Living organisms have evolved intricate systems to harvest trace elements from the environment, to control their intracellular levels, and to ensure adequate delivery to the various organs and cellular compartments. Copper is one of these trace elements. It is at the same time essential for life but also highly toxic, not least because it facilitates the generation of reactive oxygen species. In mammals, copper uptake in the intestine and copper delivery into other organs are mediated by the copper importer Ctr1. Drosophila has three Ctr1 homologs: Ctr1A, Ctr1B, and Ctr1C. Earlier work has shown that Ctr1A is an essential gene that is ubiquitously expressed throughout development, whereas Ctr1B is responsible for efficient copper uptake in the intestine. Here, we characterize the function of Ctr1C and show that it functions as a copper importer in the male germline, specifically in maturing spermatocytes and mature sperm. We further demonstrate that loss of Ctr1C in a Ctr1B mutant background results in progressive loss of male fertility that can be rescued by copper supplementation to the food. These findings hint at a link between copper and male fertility, which might also explain the high Ctr1 expression in mature mammalian spermatozoa. In both mammals and Drosophila, the X chromosome is known to be inactivated in the male germline. In accordance with such a scenario, we provide evidence that in Drosophila, the autosomal Ctr1C gene originated as a retrogene copy of the X-linked Ctr1A, thus maintaining copper delivery during male spermatogenesis.

Conserving Africa's wildlife and wildlands through the COVID-19 crisis and beyond.

The SARS-CoV-2 virus and COVID-19 illness are driving a global crisis. Governments have responded by restricting human movement, which has reduced economic activity. These changes may benefit biodiversity conservation in some ways, but in Africa, we contend that the net conservation impacts of COVID-19 will be strongly negative. Here, we describe how the crisis creates a perfect storm of reduced funding, restrictions on the operations of conservation agencies, and elevated human threats to nature. We identify the immediate steps necessary to address these challenges and support ongoing conservation efforts. We then highlight systemic flaws in contemporary conservation and identify opportunities to restructure for greater resilience. Finally, we emphasize the critical importance of conserving habitat and regulating unsafe wildlife trade practices to reduce the risk of future pandemics.

Characterization of metal-responsive transcription factor (MTF-1) from the giant rodent capybara reveals features in common with human as well as with small rodents (mouse, rat). Short communication.

From mammals to insects, metal-responsive transcription factor 1 (MTF-1) is essential for the activation of metallothionein genes upon heavy-metal load. We have previously found that human MTF-1 induces a stronger metal response than mouse MTF-1. The latter differs from the human one in a number of amino acid positions and is also shorter by 78 aa at its C-terminus. We reasoned that the weaker metal inducibility might be associated with a lesser demand for tight metal homeostasis in a low-weight, short-lived animal, and thus set out to determine the sequence of MTF-1 from the largest living rodent, the Brazilian capybara that can reach 65 kg and also has a considerably longer life span than smaller rodents. An expression clone for capybara MTF-1 was then tested for its activity in both mouse and human cells. Our analysis revealed three unexpected features: i) capybara MTF-1 in terms of amino acid sequence is much more closely related to human than to mouse MTF-1, suggesting an accelerated evolution of MTF-1 in the evolutionary branch leading to small rodents; ii) capybara MTF-1 is even 32 aa shorter at its C-terminus than mouse MTF-1, and iii) in an activity test, it is not more active than mouse MTF-1. The latter two findings might indicate that capybara has evolved in an environment with low heavy-metal load.

Enteral exsorption of acetaminophen after intravenous injection in rats: influence of activated charcoal on this clearance path.

The fate of acetaminophen after intravenous injection in whole bowel-irrigated rats (n = 40) and the influence of activated charcoal on the kinetics were investigated. After randomization to four groups (n = 10, each group), plasma concentration and the quantities of acetaminophen and metabolites excreted into bile, urine and intestine were determined using an in vivo model with or without orally administered activated charcoal and with or without bile duct cannulation. The cumulative amount of acetaminiphen and metabolites exsorbed into the small intestine within 3.5 hr after intravenous injection was about 20% of dose in the animals with bile duct cannulation and about 7% of dose in the animals without. Correspondingly, about 13% of dose was detected in the externalized bile. Activated charcoal did not influence the amount exsorbed into the small intestine. Terminal half-life in plasma ranged from 35 to 51 min. within the four treatment groups without statistically significant difference (P = 0.152). Correspondingly, the area under the curve did not vary much and ranged between 2.6 and 3.3 g/min./l (P = 0.392). Deposition of acetaminophen and metabolites in liver and kidney after 3.5 hr was marginal and ranged between 0.02% and 0.6% of the dose within all groups. The excretion of acetaminophen and metabolites into urine varied strikingly between 31% and 56% of the dose within all groups and correlated with diuresis. The lack of effect of activated charcoal on the elimination of acetaminophen and metabolites may be due to the small amount of the drug being exsorbed into the intestine or the reduced adsorbent capacity of activated charcoal to acetaminophen and metabolites, which also could be influenced by inadequate luminal stirring.

Physiological consequences of phasic insulin release in the normal animal.

The dose-response relationship between the hepatic sinusoidal insulin level and glucose production by the liver is such that a half-maximally effective concentration is at or slightly below the hormone levels seen basally after an overnight fast. In the normal individual, the direct effect of the hormone on the hepatocyte is far more important in restraining glucose production than its indirect effect mediated via a suppression of lipolysis. Because insulin regulates the liver in a direct fashion, its effect occurs within several minutes. Thus, the speed with which insulin works and the sensitivity of the liver to it predict that first-phase insulin release should have a significant effect in quickly suppressing hepatic glucose production. On the other hand, nonhepatic tissues are much less sensitive to insulin and respond slowly as a result of the need for insulin to cross the endothelial barrier. As a result, first-phase insulin is unlikely to significantly alter peripheral glucose disposal. Simulation studies in humans and dogs in which the effects of first-phase insulin were simulated confirmed the aforementioned predictions. In addition, they confirmed the ability of second-phase insulin release to have significant effects on both glucose production and utilization.

Retinal patterning by Pax6-dependent cell adhesion molecules.

Long-standing evidence gained from Pax6 mutant embryos pointed to an involvement of Pax6-dependent cell adhesion molecules in patterning the central nervous system and, in particular, the retina. However, direct evidence for such pathways remained elusive. We here present direct evidence that knockdown of Pax6 expression by morpholino antisense molecules in Xenopus embryos and knockdown of maternal N-cadherin (mNcad), N-cadherin (Ncad) and neural cell adhesion molecule (NCAM) produce similar phenotypes. Eye formation is reduced and retinal lamination is heavily disorganized. In Pax6 knockdown embryos, the levels of mRNAs coding for these cell adhesion molecules are markedly reduced. Overexpression of Pax6 efficiently rescues the phenotype of Pax6 knockdown embryos and restores expression of these putative target genes. Rescue of Pax6-deficiency by the putative target gene mNcad moderately rescues eye formation. The promoters of the genes coding for cell adhesion molecules contain several putative Pax6 binding sites, as determined by computer analysis. Chromatin immunoprecipitation shows that, in embryonic heads, Pax6 binds to promoter regions containing such predicted binding sites. Thus, several cell adhesion molecules are direct target genes of Pax6 and cooperate in retinal patterning.

Tissue distribution and excretion of myosmine after i.v. administration to Long-Evans rats using quantitative whole-body autoradiography.

Occurrence of the tobacco alkaloid myosmine has been proven in various staple foods, vegetables and fruits. Myosmine can be easily activated by nitrosation yielding 4-hydroxy-1-(3-pyridyl)-butanone (HPB) and the esophageal carcinogen N'-nitrosonornicotine. Most of the reaction products after myosmine peroxidation were also identified as urinary metabolites after oral administration to rats. Whole-body autoradiography with freeze dried or multiple solvent extracted tissue sections was used to trace [2'-(14)C]myosmine (0.1 mCi/kg bw) 0.1, 0.25, 1, 4 and 24 h after i.v. injection in Long-Evans rats. In addition, in vitro binding of radioactivity to esophageal and eye tissue was determined and excretion of radioactivity via urine and feces was quantified. Radioactivity is rapidly eliminated by renal excretion. Approximately 30% of the administered radioactivity was recovered in urine within the first 4 h and excretion with urine (72%) and feces (15%) was nearly complete after 24 h. A rapid concentration of radioactivity can be seen in the stomach and in the salivary and lachrymal glands. Rats killed 1 and 4 h after treatment showed by far the highest labeling in the accessory genital gland. High levels of nonextractable radioactivity were present in esophageal tissue and melanin. The half lives for the disappearance of radioactivity from various tissues are in the order of about 1 h. Eye and esophagus sections both showed nonextractable labeling after in vitro incubation with (14)C-myosmine. In conclusion, the toxicological significance of myosmine accumulation in esophagus and accessory genital gland requires further investigations. Hair analysis might be applicable for myosmine biomonitoring, because of possible enrichment in melanin containing tissues.

Diet-induced changes in membrane gangliosides in rat intestinal mucosa, plasma and brain.

OBJECTIVES: The objective of this study was to determine if dietary gangliosides induce changes in the ganglioside content of intestinal mucosa, plasma and brain and to identify where GM3 and GD3 are localized in the enterocyte membrane. METHODS: Male 18-day-old Sprague-Dawley rats were fed a semipurified diet containing 20% (w/w) fat. The control diet contained triglyceride, reflecting the fat formulation of an existing infant formula. Two experimental diets were formulated by adding sphingomyelin (1% w/w of total fat) or a ganglioside-enriched lipid (0.1% w/w of total fat) to the control diet fat. The ganglioside fraction of ganglioside-enriched lipid diet contained more than 80% GD3. After 2 weeks of feeding, the total and individual ganglioside and cholesterol content was measured in small intestinal mucosa, plasma and brain. RESULTS: The ganglioside-enriched lipid diet significantly increased total gangliosides in the intestinal mucosa, plasma and brain compared with the control diet. The ganglioside-enriched lipid diet significantly increased the level of GD3 (7.5% w/w) in the intestine compared with control (3.2% w/w) while decreasing the level of GM3, the major ganglioside in the intestine. The ratio of cholesterol to ganglioside in the intestinal mucosa, plasma and brain decreased significantly in rats fed the ganglioside-enriched lipid diet compared with controls. Confocal microscopy showed that GM3 is exclusively localized in the apical membrane of the enterocyte whereas GD3 is primarily localized in the basolateral membrane. CONCLUSIONS: : The authors conclude that dietary ganglioside is absorbed in the small intestine and transported to different membrane sites, altering ganglioside levels in the intestinal mucosa, plasma and brain and thus possibly having the potential to change developing enterocyte function (and possibly that of other cell lines).