Cutting Edge: Characterization of Low Copy Number Human Angiotensin-Converting Enzyme 2-Transgenic Mice as an Improved Model of SARS-CoV-2 Infection

A popular mouse model of COVID-19, the K18-hACE2 mouse, expresses the SARS-coronavirus entry receptor, human angiotensin-converting enzyme 2 (hACE2) driven by the keratin-18 promoter. SARS-CoV-2-infected K18-hACE2 mice exhibit neuropathology not representative of human infection. They contain eight transgene (Tg) copies, leading to excess hACE2 expression and rampant viral replication. We generated two new lines of K18-hACE2 mice encoding one and two copies of hACE2 (1-hACE2-Tg and 2-hACE2-Tg, respectively). Relative to the original strain (called 8-hACE2-Tg in this study), 2-hACE2-Tg mice exhibited lower mortality, with less viral replication in the lung and brain. Furthermore, 1-hACE2-Tg mice exhibited no mortality and had no detectable virus in the brain; yet, they exhibited clear viral replication in the lung. All three strains showed SARS-CoV-2-related weight loss commensurate with the mortality rates. 1-hACE2-Tg mice mounted detectable primary and memory T effector cell and Ab responses. We conclude that these strains provide improved models to study hACE2-mediated viral infections.

Gene Editing With CRISPR/Cas9 RNA-Directed Nuclease

Genetic engineering of model organisms and cultured cells has for decades provided important insights into the mechanisms underlying cardiovascular development and disease. In the past few years the development of several nuclease systems has broadened the range of model/cell systems that can be engineered. Of these, the CRISPR (clustered regularly interspersed short palindromic repeats)/Cas9 (CRISPR-associated protein 9) system has become the favorite for its ease of application. Here we will review this RNA-guided nuclease system for gene editing with respect to its usefulness for cardiovascular studies and with an eye toward potential therapy. Studies on its off-target activity, along with approaches to minimize this activity will be given. The advantages of gene editing versus gene targeting in embryonic stem cells, including the breadth of species and cell types to which it is applicable, will be discussed. We will also cover its use in iPSC for research and possible therapeutic purposes; and we will review its use in muscular dystrophy studies where considerable progress has been made toward dystrophin correction in mice. The CRISPR/Ca9s system is also being used for high-throughput screening of genes, gene regulatory regions, and long noncoding RNAs. In addition, the CRISPR system is being used for nongene-editing purposes such as activation and inhibition of gene expression, as well as for fluorescence tagging of chromosomal regions and individual mRNAs to track their cellular location. Finally, an approach to circumvent the inability of post-mitotic cells to support homologous recombination-based gene editing will be presented. In conclusion, applications of the CRISPR/Cas system are expanding at a breath-taking pace and are revolutionizing approaches to gain a better understanding of human diseases.

Possibility for using of two Paulownia lines as a tool for remediation of heavy metal contaminated soil

One-year-old two Paulownia lines (Ptomentosa x fortunei--TF 01 and R elongata x fortunei--EF 02) were grown, as pot experiment, in soil collected from the field of waste depository of Kremikovtzi ferrous metallurgical industry near Sofia. The soil was heavily polluted with Cd. Metals content (Ca, Mg, K, Na, Cd, Cu, Pb, Zn and Fe) in soil and its distribution in roots, stems and leaves of both lines was studied. The results showed that Ca and K accumulated more in stem, Mg, Na, Fe and Cd in root, while Pb, Cu and Zn in the leaves of both lines. The bloaccumulation factor (BF) and translocation factor (TF) were evaluated in order to determine the potential of plants in removing metals from contaminated soil. The BF for Fe, Pb, Cu and Zn in TF 01 line exceeded that of EF 02 line--5.6; 1.03; 1.20; 1.14 times, respectively. TF was higher in TF 01 line for Fe, Pb and Cd (6.0; 1.92 and 1.03, respectively), but not for Cu and Zn. The success of phytoremediation depends on plant growth and restricted distribution of heavy metals in shoots. Our results showed that stem length and total leaf area of Paulownia elongata x fortunei were higher than Paulownia tomentosa x fortuneibut BF for Cu and Zn and TF for Pb was less. BF for Cd was 1.7 times higher and TF for Zn was 1.03 times higher in Paulownia elongata x fortunei. Selected two lines (P. tomentosa x fortunei--TF 01 and P elongataxfortunei--EF02) were accumulators of Cu, Zn and Cd. Paulownia tomentosax fortunei accumulated more Pb and Zn in aboveground parts, while Paulownia elongata x fortunei--accumulated Zn only. These lines proved to be a promising species for phytoremediation of heavy metal polluted soils due to high biomass productivity.

Generation of mice with a conditional allele for the transforming growth factor beta3 gene

The transforming growth factor beta (TGFβ) pathway is involved in embryonic development and several inherited and acquired human diseases. The gene for TGFβ3 (Tgfb3) encodes one of the three ligands for TGFβ receptors. It is widely expressed in the embryo and its mutation or misexpression is found in human diseases. Tgfb3-/- mice die at birth from cleft palate, precluding functional studies in adults. Here, we generated mice in which exon 6 of Tgfb3 was flanked with LoxP sites (Tgfb3flox/flox). The adult mice were normal and fertile. EIIa-Cre-mediated deletion of exon 6 in Tgfb3flox/flox mice efficiently generated Tgfb3 conditional knockout (Tgfb3cko/cko) mice which died at birth from the same cleft palate defect as Tgfb3-/- mice, indicating that the conditional and knockout alleles are functionally equivalent. This Tgfb3cko allele will now enable studies of TGFβ3 function in different cell or tissue types in embryonic development and during adulthood.

Functional selectivity in cannabinoid signaling

Cannabinoid (CB) agonists exhibit numerous potentially useful pharmacological properties, but unwanted side effects limit their use in clinical practice. Thus, novel strategies are needed to identify potential CB pharmaceuticals with fewer side effects. Activated CB receptors initiate multiple parallel intracellular signal transduction cascades. In the present paper we will review experimental data indicating that structurally different classes of CB agonists may exhibit selectivity toward individual subsets of intracellular signaling pathways. In support of this, recent findings indicate that chemically distinct classes of CB agonists frequently differ in their rank order of potency to produce analgesia versus other central nervous system effects in vivo. Structurally different agonists were also found to differ in their abilities to activate individual G protein types in vitro. Since it was suggested earlier that structurally distinct CB agonists may interact differently with the CB receptors, it has been hypothesized that different classes of cannabinoid agonists may stabilize unique active CB receptor conformations, leading to functional selectivity in CB receptor signaling. In order to obtain a direct proof for this hypothesis, we recently employed a highly sensitive biophysical method, plasmon-waveguide resonance (PWR) spectroscopy. PWR experiments have provided a direct proof that structurally different CB agonists produce qualitatively distinct changes in the shape and/or membrane orientation of the CB1 receptors, leading to functional selectivity in G protein activation. We expect that by identification of CB agonists that selectively activate preferred intracellular signaling pathways novel pharmacological lead structures can be identified for the design of improved CB analgesics with fewer side effects.

Mumps outbreak in Bulgaria, 2007: a preliminary report

There is an ongoing mumps outbreak in Bulgaria, with a total of 997 cases notified between 1 January and 18 March 2007. This number includes laboratory-confirmed and probable epidemiologically-linked clinical cases in line with the EU case definition and case classification that have been adopted for mumps surveillance purposes in Bulgaria since 2005.

Insect iron binding proteins: insights from the genomes

Sequencing of the genomes of Drosophila melanogaster, Anopheles gambiae, Apis mellifera, and Bombyx mori provided an opportunity to examine the diversity and organization of genes encoding insect transferrins (Tsf) and ferritins. Information obtained from the genomes significantly advances our knowledge of these major players in insect iron metabolism and complements the results of molecular studies on their temporal, spatial, and inducible expression pattern and regulatory mechanisms conducted in diverse insect species. Analysis of genes encoding new members of the Tsf family and non-secreted ferritin subunits allows making preliminary hypotheses about their possible functions and opens possibilities to study lesser-known aspects of insect iron homeostasis. Proteomic and gene expression studies that followed the whole genome sequencing quickly contribute to defining or better understanding of the important and diverse biological roles of Tsf and ferritin, particularly their involvement in insect's defenses against oxidative stress and infection.

Characterization of mitochondrial ferritin in Drosophila

Mitochondrial function depends on iron-containing enzymes and proteins, whose maturation requires available iron for biosynthesis of iron-sulfur clusters and heme. Little is known about how mitochondrial iron homeostasis is maintained, although the recent discovery of a mitochondrial ferritin in mammals and plants has uncovered a potential key player in the process. Here, we show that Drosophila melanogaster expresses mitochondrial ferritin from an intron-containing gene. It has high similarity to the mouse and human mitochondrial ferritin sequences and, as in mammals, is expressed mainly in testis. This ferritin contains a putative mitochondrial targeting sequence and an epitope-tagged version localizes to mitochondria in transfected cells. Overexpression of mitochondrial ferritin fails to alter both total-body iron levels and iron that is bound to secretory ferritins. However, the viability of iron-deficient flies is compromised by overexpression of mitochondrial ferritin, suggesting that it may sequester iron at the expense of other important cellular functions. The conservation of mitochondrial ferritin in an insect species underscores the importance of this iron-storage molecule.

Aedes aegypti transferrin. Gene structure, expression pattern, and regulation

Mosquitoes and all other insects so far examined have an abundant haemolymph transferrin (Tsf). The exact function of these proteins has not been determined, but they may be involved in iron transport, in oogenesis and in innate immune defence against parasites and pathogens. The Tsf gene of Aedes aegypti has been cloned and sequenced. It contains a single small intron, which contrasts it to vertebrate Tsf genes that contain up to sixteen introns. The promoter region of the gene is rich in putative NF-kappaB binding sites, which is consistent with the postulated role of Tsf in insect innate immunity. Tsf message levels are very low in embryos and early larvae, but high in late larvae, pupae and adults. Western blotting experiments revealed high levels of Tsf protein in pupae and adults. Late larvae and ovaries of blood-fed mosquitoes have little intact protein, but two prominent proteolytic degradation products. These may represent biologically active peptides, as has been shown for other organisms. Tsf message is down-regulated by inorganic iron in the diet or environment, but up-regulated by a blood meal in the adult female. The up-regulation following a blood meal may, in part, be due to the decrease in juvenile hormone (JH) that is known to follow blood feeding. Treatment of blood-fed females with methoprene, an analogue of JH, resulted in decrease of the Tsf message.

Potential for using thermophilic anaerobic bacteria for bioethanol production from hemicellulose

A limited number of bacteria, yeast and fungi can convert hemicellulose or its monomers (xylose, arabinose, mannose and galactose) into ethanol with a satisfactory yield and productivity. In the present study we tested a number of thermophilic enrichment cultures, and new isolates of thermophilic anaerobic bacterial strains growing optimally at 70–80°C for their ethanol production from d-xylose. The new isolates came from different natural and man-made systems such as hot springs, paper pulp mills and brewery waste water. The test was composed of three different steps; (i) test for conversion of d-xylose into ethanol; (ii) test for viability and ethanol production in pretreated wheat straw hemicellulose hydrolysate; (iii) test for tolerance against high d-xylose concentrations. A total of 86 enrichment cultures and 58 pure cultures were tested and five candidates were selected which successfully fulfilled the criteria defined for the screening test.

Drosophila melanogaster ferritin: cDNA encoding a light chain homologue, temporal and tissue specific expression of both subunit types

Drosophila melanogaster secreted ferritin like the cytosolic ferritins of other organisms is composed of two subunits, a heavy chain homologue (HCH) and a light chain homologue (LCH). We report the cloning of a cDNA encoding the ferritin LCH of this insect. As predicted from the gene sequence, it contains no iron responsive element (IRE). Northern blot analysis reveals two mRNAs that differ in length due to the choice of polyadenylation signals. Message levels vary through the life cycle of the fly and are markedly increased by high levels of dietary iron. The gut is the main site of increased message synthesis and iron preferentially increases the amount of shorter messages. Western blotting reveals that LCH is the predominant ferritin subunit in all life stages. The amount of LCH protein corresponds well with the message levels in control animals, while in iron-fed animals LCH does not increase proportionally with the message levels. In contrast, the amount of HCH is less than that would be predicted from message levels in control animals, but corresponds well in iron-fed animals. Ferritin is abundant in gut and hemolymph of larvae and adults and in ovaries of adult flies. At pupariation, ferritin becomes more abundant in hemolymph than in other tissues.

Organization of the ferritin genes in Drosophila melanogaster

The organization of two closely clustered genes, Fer1HCH and Fer2LCH, encoding the heavy-chain homolog (HCH) and the light-chain homolog (LCH) subunits of Drosophila melanogaster ferritin are reported here. The 5019-bp sequence of the cluster was assembled from genomic fragments obtained by polymerase chain reaction (PCR) amplification of genomic DNA and from sequences obtained from the Berkeley Drosophila Genome Project (BDGP) (http://www.fruitfly.org). These genes, located at position 99F1, have different exon-intron structures (Fer1HCH has three introns and Fer2LCH has two introns) and are divergently transcribed. Computer analysis of the possibly shared promoter regions revealed the presence of putative metal regulatory elements (MREs), a finding consistent with the upregulation of these genes by iron, and putative NF-kappaB-like binding sites. The structure of two other invertebrate ferritin genes, from the nematode Caenorhabditis elegans (located on chromosomes I and V), was also analyzed. Both nematode genes have two introns, lack iron-responsive elements (IREs), and encode ferritin subunits similar to vertebrate H chains. These findings, along with comparisons of ferritin genes from invertebrates, vertebrates, and plants, suggest that the specialization of ferritin H and L type chains, the complex exon-intron organization of plant and vertebrate genes, and the use of the IRE/iron regulatory protein (IRP) mechanism for regulation of ferritin synthesis are recent evolutionary acquisitions.

Iron availability dramatically alters the distribution of ferritin subunit messages in Drosophila melanogaster

Insect ferritins have subunits homologous to the heavy and light chains of vertebrate ferritins. Cloning and sequence of the heavy chain homologue (HCH) of Drosophila melanogaster ferritin subunit have been reported earlier. When Northern blots of D. melanogaster RNA were probed with a cDNA for this HCH, three bands were observed. It was shown that these represented at least four classes of mRNA of various lengths. The polymorphism results from alternative splicing of an intron in the 5' untranslated region (UTR) that contains the iron-responsive element (IRE) and from two alternative polyadenylation sites in the 3' UTR. This has also been reported by others [Lind, M. I., Ekengren, S., Melefors, O. & Söderhäll, K. (1998) FEBS Lett. 436, 476-482]. By hybridizing Northern blots with specific probes, it has been shown that the relative proportions of the messages vary with the life stage and especially with iron supplementation of the diet. Iron significantly increases the amount of ferritin HCH messages and dramatically shifts the balance toward those messages that lack an IRE and/or have a short 3' UTR. In the larvae this change takes place in the gut, but not in the fat body. We speculate that this dramatic shift in message distribution may result from an effect of iron on the rate of transcription or message degradation, or from an effect on the splicing process itself. Synthesis of ferritin HCH subunit mRNAs that lack an IRE may be important under conditions of iron overload.

Drosophila melanogaster transferrin. Cloning, deduced protein sequence, expression during the life cycle, gene localization and up-regulation on bacterial infection

Drosophila melanogaster transferrin cDNA was cloned from an ovarian cDNA library by using a PCR fragment amplified by two primers designed from other dipteran transferrin sequences. The clone (2035 bp) encodes a protein of 641 amino acids containing a signal peptide of 29 amino acids. Like other insect transferrins, Drosophila transferrin appears to have a functional iron-binding site only in the N-terminal lobe. The C-terminal lobe lacks iron-binding residues found in other transferrins, and has large deletions which make it much smaller than functional C-terminal lobes in other transferrins. In-situ hybridization using a digoxigenin labeled transferrin cDNA probe revealed that the gene is located at position 17B1-2 on the X chromosome. Northern blot analysis showed that transferrin mRNA was present in the larval, pupal and adult stages, but was not detectable in the embryo. Iron supplementation of the diet resulted in lower levels of transferrin mRNA. When adult flies were inoculated with bacteria (Escherichia coli), transferrin mRNA synthesis was markedly increased relative to controls.

Study of erythrocytes, hemoglobin levels, and menstrual cycle characteristics of women exposed to aromatic hydrocarbons

OBJECTIVES

The impact of occupational hazards on erythrocyte and hemoglobin levels and menstrual cycle characteristics in women exposed to aromatic hydrocarbons was studied. The investigated cohort consisted of 110 women exposed to benzene, toluene, xylene and styrene while working in the transport and storage of petrochemical products (TSPP), the laboratory for the control of aromatic hydrocarbons (LCAH), and rubber and latex (RL) production at the biggest petrochemical plant in Bulgaria, Neftochim. Controls consisted of 45 women from the administrative personnel in the same plant.

METHODS

Questionnaires were administrated to all participants to obtain self-reported demographic data, data on characteristics of the menstrual cycle, and psychosomatic symptoms. Erythrocyte counts (RBC) and hemoglobin (HGB) levels were determined by the semiautomatic hematology analyzer Serono System 190, USA. All subjects had signed an informed consent.

RESULTS

The mean RBC counts and HGB levels of the women from the LCAH and TSPP departments were statistically significantly lower than those of the control group. We found statistically significant differences in all exposed groups in comparison with controls when the dose-response relationship was investigated. No statistically significant differences were found in menstrual cycle characteristics (duration of the menstrual cycle, days and quantity of bleeding) between the subjects exposed and the controls in all age groups investigated, but the numbers were too small to allow definite conclusions.

CONCLUSIONS

The lowering of HGB levels and RBC counts in the investigated women were mainly due to the direct influence of aromatic hydrocarbons in the working environment on hematopoiesis. The studied group was too small to enable us to determine the impact of aromatic hydrocarbons on menstrual cycle characteristics, and the possible combination of these effects.

Isolation and properties of Drosophila melanogaster ferritin--molecular cloning of a cDNA that encodes one subunit, and localization of the gene on the third chromosome

Ferritin was purified from iron-fed Drosophila melanogaster extracts by centrifugation in a gradient of potassium bromide. On polyacrylamide gel electrophoresis, the product showed two protein bands corresponding to the ferritin monomer and dimer. Electrophoresis following dissociation with SDS and 2-mercaptoethanol revealed three strong bands of approximately 25, 26, and 28 kDa. N-terminal amino acid sequences were identical for the 25-kDa and 26-kDa subunits, but different for the 28-kDa subunit. Conserved ferritin PCR primers were used to amplify a 360-bp cDNA product, which was used to isolate a clone from a D. melanogaster cDNA library that contained the complete coding sequence for a ferritin subunit. Additional 5' sequence obtained by the RACE method revealed the presence of a putative iron regulatory element. The PCR product was also used to locate the position of the ferritin subunit gene at region 99F on the right arm of the third chromosome. The deduced amino acid sequence of the D. melanogaster ferritin subunit contained a signal sequence and resembled most closely ferritin of the mosquito Aedes aegypti. The evolution of ferritin sequences is discussed.