Laboratory mice with a wild microbiota generate strong allergic immune responses

Allergic disorders are caused by a combination of hereditary and environmental factors. The hygiene hypothesis postulates that early-life microbial exposures impede the development of subsequent allergic disease. Recently developed "wildling" mice are genetically identical to standard laboratory specific pathogen-free (SPF) mice but are housed under seminatural conditions and have rich microbial exposures from birth. Thus, by comparing conventional SPF mice with wildlings, we can uncouple the impact of lifelong microbial exposures from genetic factors on the allergic immune response. We found that wildlings developed larger populations of antigen-experienced T cells than conventional SPF mice, which included interleukin-10-producing CD4 T cells specific for commensal Lactobacilli strains and allergy-promoting T helper 2 (TH2) cells. In models of airway exposure to house dust mite (HDM), recombinant interleukin-33, or Alternaria alternata, wildlings developed strong allergic inflammation, characterized by eosinophil recruitment, goblet cell metaplasia, and antigen-specific immunoglobulin G1 (IgG1) and IgE responses. Wildlings developed robust de novo TH2 cell responses to incoming allergens, whereas preexisting TH2 cells could also be recruited into the allergic immune response in a cytokine-driven and TCR-independent fashion. Thus, wildling mice, which experience diverse and lifelong microbial exposures, were not protected from developing pathological allergic immune responses. Instead, wildlings mounted robust allergic responses to incoming allergens, shedding new light on the hygiene hypothesis.

Reverse genetics of parrot bornavirus 4 reveals a unique splicing of the glycoprotein gene that affects viral propagation

Viruses can utilize host splicing machinery to enable the expression of multiple genes from a limited-sized genome. Orthobornaviruses use alternative splicing to regulate the expression level of viral proteins and achieve efficient viral replication in the nucleus. Although more than 20 orthobornaviruses have been identified belonging to eight different viral species, virus-specific splicing has not been demonstrated. Here, we demonstrate that the glycoprotein (G) transcript of parrot bornavirus 4 (PaBV-4; species Orthobornavirus alphapsittaciforme), a highly virulent virus in psittacines, undergoes mRNA splicing and expresses a soluble isoform termed sGP. Interestingly, the splicing donor for sGP is not conserved in other orthobornaviruses, including those belonging to the same orthobornavirus species, suggesting that this splicing has evolved as a PaBV-4-specific event. We have also shown that exogenous expression of sGP does not affect PaBV-4 replication or de novo virion infectivity. In this study, to investigate the role of sGP in viral replication, we established a reverse genetics system for PaBV-4 by using avian cell lines and generated a recombinant virus lacking the spliced mRNA for sGP. Using the recombinant viruses, we show that the replication of the sGP-deficient virus is significantly slower than that of the wild-type virus and that the exogenous expression of sGP cannot restore its propagation efficiency. These results suggest that autologous or controlled expression of sGP by splicing may be important for PaBV-4 propagation. The reverse genetics system for avian bornaviruses developed here will be a powerful tool for understanding the replication strategies and pathogenesis of avian orthobornaviruses. IMPORTANCE Parrot bornavirus 4 (PaBV-4) is the dominant cause of proventricular dilatation disease, a severe gastrointestinal and central nervous system disease among avian bornaviruses. In this study, we discovered that PaBV-4 expresses a soluble isoform of glycoprotein (G), called sGP, through alternative splicing of the G mRNA, which is unique to this virus. To understand the role of sGP in viral replication, we generated recombinant PaBV-4 lacking the newly identified splicing donor site for sGP using a reverse genetics system and found that its propagation was significantly slower than that of the wild-type virus, suggesting that sGP plays an essential role in PaBV-4 infection. Our results provide important insights not only into the replication strategy but also into the pathogenesis of PaBV-4, which is the most prevalent bornavirus in captive psittacines worldwide.

M cell maturation and cDC activation determine the onset of adaptive immune priming in the neonatal Peyer's patch

Early-life immune development is critical to long-term host health. However, the mechanisms that determine the pace of postnatal immune maturation are not fully resolved. Here, we analyzed mononuclear phagocytes (MNPs) in small intestinal Peyer's patches (PPs), the primary inductive site of intestinal immunity. Conventional type 1 and 2 dendritic cells (cDC1 and cDC2) and RORgt+ antigen-presenting cells (RORgt+ APC) exhibited significant age-dependent changes in subset composition, tissue distribution, and reduced cell maturation, subsequently resulting in a lack in CD4+ T cell priming during the postnatal period. Microbial cues contributed but could not fully explain the discrepancies in MNP maturation. Type I interferon (IFN) accelerated MNP maturation but IFN signaling did not represent the physiological stimulus. Instead, follicle-associated epithelium (FAE) M cell differentiation was required and sufficient to drive postweaning PP MNP maturation. Together, our results highlight the role of FAE M cell differentiation and MNP maturation in postnatal immune development.

Cytomegalovirus subverts macrophage identity

Cytomegaloviruses (CMVs) have co-evolved with their mammalian hosts for millions of years, leading to remarkable host specificity and high infection prevalence. Macrophages, which already populate barrier tissues in the embryo, are the predominant immune cells at potential CMV entry sites. Here we show that, upon CMV infection, macrophages undergo a morphological, immunophenotypic, and metabolic transformation process with features of stemness, altered migration, enhanced invasiveness, and provision of the cell cycle machinery for viral proliferation. This complex process depends on Wnt signaling and the transcription factor ZEB1. In pulmonary infection, mouse CMV primarily targets and reprograms alveolar macrophages, which alters lung physiology and facilitates primary CMV and secondary bacterial infection by attenuating the inflammatory response. Thus, CMV profoundly perturbs macrophage identity beyond established limits of plasticity and rewires specific differentiation processes, allowing viral spread and impairing innate tissue immunity.

The Mammalian Metaorganism: A Holistic View on How Microbes of All Kingdoms and Niches Shape Local and Systemic Immunity

The field of microbiome research has developed rapidly over the past decades and has become a topic of major interest to basic, preclinical, and clinical research, the pharmaceutical industry as well as the general public. The microbiome is a complex and diverse ecosystem and defined as the collection of all host-associated microorganisms and their genes. It is acquired through vertical transmission and environmental exposure and includes microbes of all kingdoms: bacteria, archaea, prokaryotic and eukaryotic viruses, fungi, protozoa, and the meiofauna. These microorganisms co-evolved with their respective hosts over millions of years, thereby establishing a mutually beneficial, symbiotic relationship on all epithelial barriers. Thus, the microbiome plays a pivotal role in virtually every aspect of mammalian physiology, particularly in the development, homeostasis, and function of the immune system. Consequently, the combination of the host genome and the microbial genome, together referred to as the metagenome, largely drives the mammalian phenotype. So far, the majority of studies have unilaterally focused on the gastrointestinal bacterial microbiota. However, recent work illustrating the impact of viruses, fungi, and protozoa on host immunity urges us towards a holistic view of the mammalian microbiome and the appreciation for its non-bacterial kingdoms. In addition, the importance of microbiota on epithelial barriers other than the gut as well as their systemic effects via microbially-derived biologically active compounds is increasingly recognized. Here, we want to provide a brief but comprehensive overview of the most important findings and the current knowledge on how microbes of all kingdoms and microbial niches shape local and systemic immunity in health and disease.

Viral vector vaccines expressing nucleoprotein and phosphoprotein genes of avian bornaviruses ameliorate homologous challenge infections in cockatiels and common canaries

Avian bornaviruses are causative agents of proventricular dilatation disease (PDD), an often fatal disease of parrots and related species (order Psittaciformes) which is widely distributed in captive psittacine populations and may affect endangered species. Here, we established a vaccination strategy employing two different well described viral vectors, namely recombinant Newcastle disease virus (NDV) and modified vaccinia virus Ankara (MVA) that were engineered to express the phosphoprotein and nucleoprotein genes of two avian bornaviruses, parrot bornavirus 4 (PaBV-4) and canary bornavirus 2 (CnBV-2). When combined in a heterologous prime/boost vaccination regime, NDV and MVA vaccine viruses established self-limiting infections and induced a bornavirus-specific humoral immune response in cockatiels (Nymphicus hollandicus) and common canaries (Serinus canaria forma domestica). After challenge infection with a homologous bornavirus, shedding of bornavirus RNA and viral loads in tissue samples were significantly reduced in immunized birds, indicating that vaccination markedly delayed the course of infection. However, cockatiels still developed signs of PDD if the vaccine failed to prevent viral persistence. Our work demonstrates that avian bornavirus infections can be repressed by vaccine-induced immunity. It represents a first crucial step towards a protective vaccination strategy to combat PDD in psittacine birds.

[Maxillary ameloblastoma extending into the sinonasal tract]

Maxillary ameloblastomas can extensively expand into the paranasal sinuses or even the nasal cavity due to a slow growth pattern. Sinusitis is rarely the first tumor-related complaint. Due to the various growth forms of ameloblastomas the challenging histological differential diagnosis includes several other odontogenic as well as benign and malignant non-odontogenic tumors, e.g. tumors from the mucosa of the paranasal sinuses, salivary glands and Rathke's pouch. Despite the radical surgical approach a complete resection with wide margins cannot always be achieved. Maxillary ameloblastomas show the highest recurrence rates.

Prevalence of risk determinants for metformin-associated lactic acidosis and metformin utilization in the study of health in pomerania

Risk determinants for the life threatening complication of metformin-associated lactic acidosis are frequently disregarded. Our first aim was to investigate the prevalence of risk determinants in subjects with type 2 diabetes mellitus (DM2) taking metformin compared to subjects with nonmetformin treatment. Our second aim was to estimate the proportion of subjects with alternative drug-treatment, and no risk determinants, which would probably benefit from metformin. The Study of Health in Pomerania is a population-based health survey including 322 DM2 subjects. Risk determinants were assessed by personal interview, ultrasound, and laboratory analysis. Among the subjects with DM2 n=92 (28.6%) were treated with metformin, n=162 (50.3%) with alternative medication, and n=68 (21.1%) with diet. The prevalence of at least one risk determinant was 65% [corrected] for metformin-users. There was no difference in number and type of risk determinants. Heart failure, angina pectoris, and liver disorders presented the most frequent risk determinants. Current risk determinants for metformin-associated lactic acidosis are largely disregarded. Improved selection of patients can result in safe metformin utilization in one quarter of subjects on DM2 related drug treatment. Risk determinants need to be revised. A more practical definition of risk determinants would improve prescription adherence.

Metformin-associated lactic acidosis in patients with renal impairment solely due to drug accumulation?

AIM

We suspect that the life-threatening complication of metformin-associated lactic acidosis, solely due to drug accumulation following renal impairment, occurs more frequently than that previously reported and is not necessarily associated with other predisposing factors for lactic acidosis.

METHODS

During a period of 13 months, at a tertiary referral centre, the incidence of lactic acidosis of any aetiology was 12.8% [67 of 524 total intensive care unit (ICU) admissions]. Metformin-associated lactic acidosis solely as the result of drug accumulation was diagnosed in 6% of all the patients suffering from lactic acidosis (4 of 67 patients).

RESULTS

These patients presented with severe circulatory shock due to lactic acidosis. We could not identify any predisposing factor for lactic acidosis other than renal impairment. Intercurrent deterioration of diabetic nephropathy was suspected to be responsible for the accumulation of metformin followed by lactic acidosis, finally resulting in multiorgan failure. The diagnosis was supported by extensively elevated serum levels of metformin. Two patients died during ICU treatment.

CONCLUSIONS

Our data indicate that the incidence of metformin-associated lactic acidosis solely due to metformin accumulation is possible and underestimated. Symptoms of metformin-associated lactic acidosis are unspecific and physicians should be aware that metformin, if prescribed in patients with renal impairment, can cause fatal lactic acidosis due to drug accumulation.

Oral bioavailability of cyclosporine: Solid lipid nanoparticles (SLN®) versus drug nanocrystals

For the development of an optimized oral formulation for cyclosporine A, 2% of this drug has been formulated in solid lipid nanoparticles (SLN, mean size 157 nm) and as nanocrystals (mean size 962 nm). The encapsulation rate of SLN was found to be 96.1%. Nanocrystals are composed of 100% of drug. For the assessment of the pharmacokinetic parameters the developed formulations have been administered via oral route to three young pigs. Comparison studies with a commercial Sandimmun Neoral/Optoral used as reference have been performed. The blood profiles observed after oral administration of the commercial microemulsion Sandimmun revealed a fast absorption of drug leading to the observation of a plasma peak above 1,000 ng/ml within the first 2 h. For drug nanocrystals most of the blood concentrations were in the range between 30 and 70 ng/ml over a period of 14 h. These values were very low, showing huge differences between the measuring time points and between the tested animals. On the contrary, administration of cyclosporine-loaded SLN led to a mean plasma profile with almost similarly low variations in comparison to the reference microemulsion, however with no initial blood peak as observed with the Sandimmun Neoral/Optoral. Comparing the area under the curves (AUC) obtained with the tested animals it could be stated that the SLN formulation avoids side effects by lacking blood concentrations higher than 1,000 ng/ml. In this study it has been proved that using SLN as a drug carrier for oral administration of cyclosporine A a low variation in bioavailability of the drug and simultaneously avoiding the plasma peak typical of the first Sandimmun formulation can be achieved.

Mutations at amino-acid 482 in the ABCG2 gene affect substrate and antagonist specificity

Recent studies have shown that mutations at amino-acid 482 in the ABCG2 gene affect the substrate specificity of the protein. To delineate the effects of these mutations clearly, human embryonic kidney cells (HEK-293) were stably transfected with wild-type 482R or mutant 482G and 482T ABCG2. By flow cytometry, mitoxantrone, BODIPY-prazosin, and Hoechst 33342 were found to be substrates of all ABCG2 proteins, while rhodamine 123, daunorubicin, and LysoTracker Green were transported only by mutant ABCG2. In cytotoxicity assays, all ABCG2 proteins conferred high levels of resistance to mitoxantrone, SN-38, and topotecan, while mutant ABCG2 also exhibited a gain of function for mitoxantrone as they conferred a four-fold greater resistance compared to wild type. Cells transfected with mutant ABCG2 were 13- to 71- fold resistant to the P-glycoprotein substrates doxorubicin, daunorubicin, epirubicin, bisantrene, and rhodamine 123 compared to cells transfected with wild-type ABCG2, which were only three- to four-fold resistant to these compounds. ABCG2 did not confer appreciable resistance to etoposide, taxol or the histone deacetylase inhibitor depsipeptide. None of the transfected cell lines demonstrated resistance to flavopiridol despite our previous observation that ABCG2-overexpressing cell lines are cross-resistant to the drug. Recently reported inhibitors of ABCG2 were evaluated and 50 μM novobiocin was found to reverse wild-type ABCG2 completely, but only reverse mutant ABCG2 partially. The studies presented here serve to underscore the importance of amino-acid 482 in defining the substrate specificity of the ABCG2 protein and raise the possibility that amino-acid 482 mutations in human cancers could affect the clinical application of antagonists for ABCG2.

Different domains of the glucagon and glucagon-like peptide-1 receptors provide the critical determinants of ligand selectivity

(1) Glucagon and glucagon-like peptide-1 (GLP-1) are homologous peptide hormones with important functions in glucose metabolism. The receptors for glucagon and GLP-1 are homologous family B G-protein coupled receptors. The GLP-1 receptor amino-terminal extracellular domain is a major determinant of glucagon/GLP-1 selectivity of the GLP-1 receptor. However, the divergent residues in glucagon and GLP-1 that determine specificity for the GLP-1 receptor amino-terminal extracellular domain are not known. Less is known about how the glucagon receptor distinguishes between glucagon and GLP-1. (2) We analysed chimeric glucagon/GLP-1 peptides for their ability to bind and activate the glucagon receptor, the GLP-1 receptor and chimeric glucagon/GLP-1 receptors. The chimeric peptide GLP-1(7-20)/glucagon(15-29) was unable to bind and activate the glucagon receptor. Substituting the glucagon receptor core domain with the GLP-1 receptor core domain (chimera A) completely rescued the affinity and potency of GLP-1(7-20)/glucagon(15-29) without compromising the affinity and potency of glucagon. Substituting transmembrane segment 1 (TM1), TM6, TM7, the third extracellular loop and the intracellular carboxy-terminus of chimera A with the corresponding glucagon receptor segments re-established the ability to distinguish GLP-1(7-20)/glucagon(15-29) from glucagon. Corroborant results were obtained with the opposite chimeric peptide glucagon(1-14)/GLP-1(21-37). (3) The results suggest that the glucagon and GLP-1 receptor amino-terminal extracellular domains determine specificity for the divergent residues in the glucagon and GLP-1 carboxy-terminals respectively. The GLP-1 receptor core domain is not a critical determinant of glucagon/GLP-1 selectivity. Conversely, the glucagon receptor core domain contains two or more sub-segments which strongly determine specificity for divergent residues in the glucagon amino-terminus.

H19 RNA binds four molecules of insulin-like growth factor II mRNA-binding protein

H19 RNA is a major oncofetal 2.5-kilobase untranslated RNA of unknown function. The maternally expressed H19 gene is located 90 kilobase pairs downstream from the paternally expressed insulin-like growth factor II (IGF-II) gene on human chromosome 11 and mouse chromosome 7; and due to their reciprocal imprinting and identical spatiotemporal expression, it is assumed that the two genes are functionally coupled. Here we show that human H19 RNA contains four attachment sites for the oncofetal IGF-II mRNA-binding protein (IMP) with apparent K(d) values in the 0.4-1.3 nm range. The multiple attachment sites are clustered within a 700-nucleotide segment encoded by exons 4 and 5. This 3'-terminal segment targets H19 RNA to lamellipodia and perinuclear regions in dispersed fibroblasts where IMP is also localized. The results suggest that IMP participates in H19 RNA localization and provides a link between the IGF-II and H19 genes at post-transcriptional events during mammalian development.

Cytotoxicity of solid lipid nanoparticles as a function of the lipid matrix and the surfactant

PURPOSE

Assessment of the in vitro cytotoxicity of solid lipid nanoparticles (SLNs) as a function of lipid matrix (Dynasan 114, Compritol ATO 888), and stabilizing surfactant (poloxamers, Tween 80, soya lecithin, and sodium dodecyl sulphate). Comparison with other colloidal carriers should determine their potential use in the clinic.

METHODS

SLNs were produced by high pressure homogenisation. Cytotoxicity was assessed by measuring the viability of HL60 cells and human granulocytes after incubation with SLNs. Particle internalisation was quantified by chemiluminescence measurements.

RESULTS

The nature of the lipid had no effect on viability; distinct differences were found for the surfactants. Binding to the SLN surface reduced markedly the cytotoxic effect of the surfactants, e.g., up to a factor of 65 for poloxamer 184. The permanent HL60 cell line-differentiated from cells with granulocyte characteristics by retinoic acid treatment-yielded results identical to freshly isolated human granulocytes. In general, the SLNs showed a lower cytotoxicity compared to polyalkylcyanoacrylate and polylactic/glycolic acid (PLA/ GA) nanoparticles.

CONCLUSIONS

Because the results are identical when using human granulocytes, differentiated HL60 cells can be used as an easily accessible in vitro test system for i.v. injectable SLN formulations. The SLNs appear suitable as a drug carrier system for potential intravenous use due to their very low cytotoxicity in vitro.

Distinct roles for light-dependent NADPH:protochlorophyllide oxidoreductases (POR) A and B during greening in higher plants

Light-dependent NADPH:protochlorophyllide oxidoreductase (POR), a nuclear-encoded plastid-localized enzyme, catalyzes the photoreduction of protochlorophyllide (Pchlide) to chlorophyllide in higher plants, algae and cyanobacteria. Angiosperms require light for chlorophyll (Chl) biosynthesis and have recently been shown to contain two POR-encoding genes, PorA and PorB, that are differentially regulated by light and developmental state. PorA expression rapidly becomes undetectable after illumination of etiolated seedlings, whereas PorB expression persists throughout greening and in adult plants. In order to study the in vivo functions of Arabidopsis POR A and POR B we have abolished the expression of PorA through the use of the phytochrome A-mediated far-red high irradiance response. Wild-type seedlings grown in continuous far-red light (cFR) display the morphology of white light (WL)-grown seedlings, but contain only traces of Chl and do not green upon transfer to WL. This cFR-induced greening defect correlates with the absence of PorA mRNA, the putative POR A protein, phototransformable Pchlide-F655, and with strongly reduced POR enzymatic activity in plant extracts. In contrast, a cFR-grown phyA mutant expresses the PorA gene, accumulates Chl and visibly greens in WL. Furthermore, constitutive overexpression of POR A in cFR-grown transgenic Arabidopsis wild-type seedlings restores Chl accumulation and WL-induced greening. These data demonstrate that POR A is required for greening and that the availability of POR A limits Chl accumulation during growth in cFR. POR B apparently provides a means to sustain light-dependent Chl biosynthesis in fully greened, mature plants in the absence of phototransformable Pchlide-F655.

Identification of NADPH:protochlorophyllide oxidoreductases A and B: a branched pathway for light-dependent chlorophyll biosynthesis in Arabidopsis thaliana

Illumination releases the arrest in chlorophyll (Chl) biosynthesis in etiolated angiosperm seedlings through the enzymatic photoreduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide), the first light-dependent step in chloroplast biogenesis. NADPH: Pchlide oxidoreductase (POR, EC 1.3.1.33), a nuclear-encoded plastid-localized enzyme, mediates this unique photoreduction. Paradoxically, light also triggers a drastic decrease in the amounts of POR activity and protein before the Chl accumulation rate reaches its maximum during greening. While investigating this seeming contradiction, we identified two distinct Arabidopsis thaliana genes encoding POR, in contrast to previous reports of only one gene in angiosperms. The genes, designated PorA and PorB, by analogy to the principal members of the phytochrome photoreceptor gene family, display dramatically different patterns of light and developmental regulation. PorA mRNA disappears within the first 4 h of greening, whereas PorB mRNA persists even after 16 h of illumination, mirroring the behavior of two distinct POR protein species. Experiments designed to help define the functions of POR A and POR B demonstrate exclusive expression of PorA in young seedlings and of PorB both in seedlings and in adult plants. Accordingly, we propose the existence of a branched light-dependent Chl biosynthesis pathway in which POR A performs a specialized function restricted to the initial stages of greening and POR B maintains Chl levels throughout angiosperm development.

Enzymatic product formation impairs both the chloroplast receptor-binding function as well as translocation competence of the NADPH: protochlorophyllide oxidoreductase, a nuclear-encoded plastid precursor protein

The key enzyme of chlorophyll biosynthesis in higher plants, the light-dependent NADPH:protochlorophyllide oxidoreductase (POR, EC 1.6.99.1), is a nuclear-encoded plastid protein. Its posttranslational transport into plastids of barley depends on the intraplastidic availability of one of its substrates, protochlorophyllide (PChlide). The precursor of POR (pPOR), synthesized from a corresponding full-length barley cDNA clone by coupling in vitro transcription and translation, is enzymatically active and converts PChlide to chlorophyllide (Chlide) in a light- and NADPH-dependent manner. Chlorophyllide formed catalytically remains tightly but noncovalently bound to the precursor protein and stabilizes a transport-incompetent conformation of pPOR. As shown by in vitro processing experiments, the chloroplast transit peptide in the Chlide-pPOR complex appears to be masked and thus is unable to physically interact with the outer plastid envelope membrane. In contrast, the chloroplast transit peptide in the naked pPOR (without its substrates and its product attached to it) and in the pPOR-substrate complexes, such as pPOR-PChlide or pPOR-PChlide-NADPH, seems to react independently of the mature region of the polypeptide, and thus is able to bind to the plastid envelope. When envelope-bound pPOR-PChlide-NADPH complexes were exposed to light during a short preincubation, the enzymatically produced Chlide slowed down the actual translocation step, giving rise to the sequential appearance of two partially processed translocation intermediates. However, ongoing translocation induced by feeding the chloroplasts delta-aminolevulinic acid, a precursor of PChlide, was able to override these two early blocks in translocation, suggesting that the plastid import machinery has a substantial capacity to denature a tightly folded, envelope-bound precursor protein. Together, our results show that pPOR with Chlide attached to it is impaired both in the ATP-dependent step of binding to a receptor protein component of the outer chloroplast envelope membrane, as well as in the PChlide-dependent step of precursor translocation.

Substrate-dependent transport of the NADPH:protochlorophyllide oxidoreductase into isolated plastids

The key regulatory enzyme of chlorophyll biosynthesis in higher plants, the light-dependent NADPH:protochlorophyllide oxidoreductase (POR), is a nuclear-encoded plastid protein. Its post-translational transport into plastids is determined by its substrate. The precursor of POR (pPOR) is taken up and processed to mature size by plastids only in the presence of protochlorophyllide (Pchlide). In etioplasts, the endogenous level of Pchlide saturates the demands for pPOR translocation. During the light-induced transformation of etioplasts into chloroplasts, the Pchlide concentration declined drastically, and isolated chloroplasts rapidly lost the ability to import the precursor enzyme. The chloroplasts' import capacity for the pPOR, however, was restored when their intraplastidic level of Pchlide was raised by incubating the organelles in the dark with delta-aminolevulinic acid, a common precursor of tetrapyrroles. Additional evidence for the involvement of intraplastidic Pchlide in regulating the transport of pPOR into plastids was provided by experiments in which barley seedlings were grown under light/dark cycles. The intraplastidic Pchlide concentration in these plants underwent a diurnal fluctuation, with a minimum at the end of the day and a maximum at the end of the night period. Chloroplasts isolated at the end of the night translocated pPOR, whereas those isolated at the end of the day did not. Our results imply that the Pchlide-dependent transport of the pPOR into plastids might be part of a novel regulatory circuit by which greening plants fine tune both the enzyme and pigment levels, thereby avoiding the wasteful degradation of the imported pPOR as well as photodestruction of free Pchlide.

Isolation and classification of chlorophyll-deficient xantha mutants of Arabidopsis thaliana

Mutant lines of Arabidopsis thaliana that are either blocked at various steps of the biosynthetic pathway of chlorophyll (Chl) or that are disturbed in one of the subsequent steps leading to the assembly of an active photosynthetic membrane were isolated by screening for Chl-deficient xantha (xan) mutants. Only mutants that segregated in a 3:1 ratio, that contained the same carotenoid spectrum as etiolated wild-type seedlings and less than 2% of the Chl of wild-type control seedlings, and whose Chl content was not affected by the addition of sucrose to the growth medium were selected for a more detailed analysis. As a final test for the classification of the selected mutants, light-grown xan mutants were vacuum-infiltrated and incubated with the common precursor of tetrapyrroles, delta-aminolevulinic acid (ALA), in the dark. Two major groups of mutants could be distinguished. Some of the mutants were blocked at various steps of the Chl pathway between ALA and protochlorophyllide (Pchlide) and did not accumulate the latter in the dark. The other mutants accumulated Pchlide in the dark regardless of whether exogenous ALA was added. This latter group could be subdivided into mutants with a biochemical lesion in a recently discovered second light-dependent Pchlide reduction step that occurs in green plants and mutants that have blocks in the assembly of Chl protein complexes. In the present work a total of seven different loci could be defined genetically in Arabidopsis that affect the synthesis of Chl and its integration into the growing photosynthetic membrane.

Expression of an oncofetal protein (OFP) in rat and human leukemia cells

A unique oncofetal protein (OFP) previously identified in rat fetal tissue and rat and human solid tumors, is now shown to be present in rat and human leukemia cells by use of a monoclonal antibody-based assay. Using a highly specific anti-rat OFP monoclonal antibody OFP has been unquivocally immunolocalized to the cytoplasm of the rat leukemia cells. The factor is rapidly released to the circulation as 50 and 55 kD species which share the immunological determinants. When leukemia cells are transplanted to normal rats, OFP increases in the circulation in a biphasic manner which may be due to immune clearance since circulating anti-OFP antibodies have been demonstrated. Induction of differentiation in the human HL-60 leukemia cell line by 13-cis-retinoic acid caused a down regulation of OFP synthesis, both intra- and extra-cellular levels dropping to essentially zero. Induction of differentiation with dibutyryl cyclic AMP caused a cessation of secretion of OFP, with a marked increase in its intracellular concentration, a condition resembling the retention in fetal cells. Leukemia cells add to a growing list of tumors previously shown to produce OFP, suggesting that OFP is intimately involved in some facet of tumorigenesis.

Halothane decreases calcium channel antagonist binding to cardiac membranes

The effect of halothane concentration on the binding of the calcium antagonist, [3H] nitrendipine (3HNTP), to rat and rabbit heart membranes was examined in vitro because it has been hypothesized that one mechanism by which halothane depresses cardiac contractility is by interfering with Ca2+ channel function. Membranes were incubated for 90 minutes in a closed system with 3HNTP and increasing concentrations of halothane. The amount of 3HNTP bound to membranes was quantified by radioligand binding technique and liquid scintillation counting. It was found in both the rat and rabbit cardiac membranes that halothane (0.4-2.0%) caused a dose-dependent decrease in specific 3HNTP binding (P less than 0.0001). The decrease in 3HNTP binding caused by halothane was also found to be reversible. These results indicate that halothane interferes with one property of the Ca2+ channel and suggest that this may be one possible mechanism for the negative inotropic action of halothane.