Neurofibromatosis-1 regulates neuronal and glial cell differentiation from neuroglial progenitors in vivo by both cAMP- and Ras-dependent mechanisms

Individuals with neurofibromatosis type 1 (NF1) develop abnormalities of both neuronal and glial cell lineages, suggesting that the NF1 protein neurofibromin is an essential regulator of neuroglial progenitor function. In this regard, Nf1-deficient embryonic telencephalic neurospheres exhibit increased self-renewal and prolonged survival as explants in vivo. Using a newly developed brain lipid binding protein (BLBP)-Cre mouse strain to study the role of neurofibromin in neural progenitor cell function in the intact animal, we now show that neuroglial progenitor Nf1 inactivation results in increased glial lineage proliferation and abnormal neuronal differentiation in vivo. Whereas the glial cell lineage abnormalities are recapitulated by activated Ras or Akt expression in vivo, the neuronal abnormalities were Ras- and Akt independent and reflected impaired cAMP generation in Nf1-deficient cells in vivo and in vitro. Together, these findings demonstrate that neurofibromin is required for normal glial and neuronal development involving separable Ras-dependent and cAMP-dependent mechanisms.     

Mammalian target of rapamycin: master regulator of cell growth in the nervous system

The mammalian target of rapamycin (mTOR) is a highly conserved serine/threonine protein kinase that regulates a number of diverse biologic processes important for cell growth and proliferation, including ribosomal biogenesis and protein translation. In this regard, hyperactivation of the mTOR signaling pathway has been demonstrated in numerous human cancers, including a number of inherited cancer syndromes in which individuals have an increased risk of developing benign and malignant tumors. Three of these inherited cancer syndromes (Lhermitte-Duclos disease, neurofibromatosis type 1, and tuberous sclerosis complex) are characterized by significant central nervous system dysfunction and brain tumor formation. Each of these disorders is caused by a genetic mutation that disrupts the expression of proteins which negatively regulate mTOR signaling, indicating that the mTOR signaling pathway is critical for appropriate brain development and function. In this review, we discuss our current understanding of the mTOR signaling pathway and its role in promoting ribosome biogenesis and cell growth. We suggest that studies of this pathway may prove useful in identifying molecular targets for biologically-based therapies of brain tumors associated with these inherited cancer syndromes as well as sporadic central nervous system tumors.     

Effect of light conditions on anatomical and biochemical aspects of somatic and zygotic embryos of hybrid larch (Larix?×?marschlinsii)

Background and Aims In conifers, mature somatic embryos and zygotic embryos appear to resemble one another physiologically and morphologically. However, phenotypes of cloned conifer embryos can be strongly influenced by a number of in vitro factors and in some instances clonal variation can exceed that found in nature. This study examines whether zygotic embryos that develop within light-opaque cones differ from somatic embryos developing in dark/light conditions in vitro. Embryogenesis in larch is well understood both in situ and in vitro and thus provides a suitable system for addressing this question.Methods Features of somatic and zygotic embryos of hybrid larch, Larix × marschlinsii, were quantified, including cotyledon numbers, protein concentration and phenol chemistry. Somatic embryos were placed either in light or darkness for the entire maturation period. Embryos at different developmental stages were embedded and sectioned for histological analysis.Key Results Light, and to a lesser degree abscisic acid (ABA), influenced accumulation of protein and phenolic compounds in somatic and zygotic embryos. Dark-grown mature somatic embryos had more protein (91·77 ± 11·26 µg protein mg^–1 f.wt) than either dark-grown zygotic embryos (62·40 ± 5·58) or light-grown somatic embryos (58·15 ± 10·02). Zygotic embryos never accumulated phenolic compounds at any stage, whereas somatic embryos stored phenolic compounds in the embryonal root caps and suspensors. Light induced the production of quercetrin (261·13 ± 9·2 µg g^–1 d.wt) in somatic embryos. Mature zygotic embryos that were removed from seeds and placed on medium in light rapidly accumulated phenolics in the embryonal root cap and hypocotyl. Delaying germination with ABA delayed phenolic compound accumulation, restricting it to the embryonal root cap.Conclusions In larch embryos, light has a negative effect on protein accumulation, but a positive effect on phenol accumulation. Light did not affect morphogenesis, e.g. cotyledon number. Somatic embryos produced different amounts of phenolics, such as quercetrin, depending on light conditions. The greatest difference was seen in the embryonal root cap in all embryo types and conditions.     

Biological and immunological comparisons of Enterobacter cloacae and Escherichia coli porins

Abstract Bacteriocin susceptibilities indicate that during cloacin DF13 uptake the F porin of Enterobacter cloacae plays a similar role to that reported for the OmpF porin of Escherichia coli during colicin A entry. The translocatory activities of these two porins during the bacteriocin uptake can be substituted by the porins D and OmpC, respectively, under conditions not requiring the receptor binding step. Using anti-peptide antibodies, a peptide located in the internal loop L3 of the Escherichia coli OmpF porin was identified in the D and F porins of Enterobacter cloacae. The results demonstrated the existence of a close relationship between porins in terms of both antigenic determinants and bacteriocin susceptibilities.     

Differential effects of cAMP in neurons and astrocytes. Role of B-raf.

Mitogen-activated protein kinase (MAPK) activation provides cell type-specific signals important for cellular differentiation, proliferation, and survival. Cyclic AMP (cAMP) has divergent effects on MAPK activity depending on whether signaling is through Ras/Raf-1 or Rap1/B-raf. We found that central nervous system-derived neurons, but not astrocytes, express B-raf. In neurons, cAMP activated MAPK in a Rap1/B-raf-dependent manner, while in astrocytes, cAMP decreased MAPK activity. Inhibition of MAPK in neurons decreased neuronal growth factor-mediated survival, and activation of MAPK by cAMP analogues rescued neurons from death. Furthermore, constitutive expression of B-raf in astrocytoma cells increased MAPK activation, as seen in neurons, and enhanced proliferation. These data provide the first experimental evidence that B-raf is the molecular switch which dominantly permits differential cAMP-dependent regulation of MAPK in neurons versus astrocytes, with important implications for both survival and proliferation.     

One or two low affinity penicillin-binding proteins may be responsible for the range of susceptibility of Enterococcus faecium to benzylpenicillin

Three benzylpenicillin-resistant, clinical isolates of Enterococcus faecium (MIC values 16-64 micrograms ml-1) contained six penicillin-binding proteins (PBPs), of which PBP5 was the most abundant and had the lowest affinity for the antibiotic. Four benzylpenicillin-susceptible strains (MIC values 0.031-0.5 microgram ml-1) were obtained as spontaneous derivatives from these above organisms. There were significant decreases in the amounts of PBP5 in each of the derivatives, with the concomitant appearance of a new, higher affinity PBP (5*) in three strains. Increased amounts of PBP5, with no changes in PBP5*, were found in several mutants with intermediate-level benzylpenicillin-resistance (MIC values 1-8 micrograms ml-1) selected from two of the susceptible strains. Examination of 18 other clinical isolates, with a wide range of susceptibilities to benzylpenicillin (MIC values 0.062-128 micrograms ml-1), showed that PBP5* was present in 13 strains, and PBP5 in all of them, but in differing amounts. The results concerning the relative amounts and relative affinities of PBPs 5* and 5 allowed the categorization of the various strains into six groups, within which organisms had somewhat similar susceptibilities to benzylpenicillin.     

On the Identifiability of Transmission Dynamic Models for Infectious Diseases

Understanding the transmission dynamics of infectious diseases is important for both biological research and public health applications. It has been widely demonstrated that statistical modeling provides a firm basis for inferring relevant epidemiological quantities from incidence and molecular data. However, the complexity of transmission dynamic models presents two challenges: (1) the likelihood function of the models is generally not computable, and computationally intensive simulation-based inference methods need to be employed, and (2) the model may not be fully identifiable from the available data. While the first difficulty can be tackled by computational and algorithmic advances, the second obstacle is more fundamental. Identifiability issues may lead to inferences that are driven more by prior assumptions than by the data themselves. We consider a popular and relatively simple yet analytically intractable model for the spread of tuberculosis based on classical IS6110 fingerprinting data. We report on the identifiability of the model, also presenting some methodological advances regarding the inference. Using likelihood approximations, we show that the reproductive value cannot be identified from the data available and that the posterior distributions obtained in previous work have likely been substantially dominated by the assumed prior distribution. Further, we show that the inferences are influenced by the assumed infectious population size, which generally has been kept fixed in previous work. We demonstrate that the infectious population size can be inferred if the remaining epidemiological parameters are already known with sufficient precision.     

Use of Learning Media by Undergraduate Medical Students in Pharmacology: A Prospective Cohort Study

The ubiquity of the internet and computer-based technologies has an increasing impact on higher education and the way students access information for learning. Moreover, there is a paucity of information about the quantitative and qualitative use of learning media by the current student generation. In this study we systematically analyzed the use of digital and non-digital learning resources by undergraduate medical students. Daily online surveys and semi-structured interviews were conducted with a cohort of 338 third year medical students enrolled in a general pharmacology course. Our data demonstrate a predominant use of digital over non-digital learning resources (69 ± 7% vs. 31 ± 7%; p < 0.01) by students. Most used media for learning were lecture slides (26.8 ± 3.0%), apps (22.0 ± 3.7%) and personal notes (15.5 ± 2.7%), followed by textbooks (> 300 pages) (10.6 ± 3.3%), internet search (7.9 ± 1.6%) and e-learning cases (7.6 ± 3.0%). When comparing learning media use of teaching vs. pre-exam self-study periods, textbooks were used significantly less during self-study (-55%; p < 0.01), while exam questions (+334%; p < 0.01) and e-learning cases (+176%; p < 0.01) were utilized more. Taken together, our study revealed a high prevalence and acceptance of digital learning resources by undergraduate medical students, in particular mobile applications.     

Accuracy and Completeness of Drug Information in Wikipedia: A Comparison with Standard Textbooks of Pharmacology

The online resource Wikipedia is increasingly used by students for knowledge acquisition and learning. However, the lack of a formal editorial review and the heterogeneous expertise of contributors often results in skepticism by educators whether Wikipedia should be recommended to students as an information source. In this study we systematically analyzed the accuracy and completeness of drug information in the German and English language versions of Wikipedia in comparison to standard textbooks of pharmacology. In addition, references, revision history and readability were evaluated. Analysis of readability was performed using the Amstad readability index and the Erste Wiener Sachtextformel. The data on indication, mechanism of action, pharmacokinetics, adverse effects and contraindications for 100 curricular drugs were retrieved from standard German textbooks of general pharmacology and compared with the corresponding articles in the German language version of Wikipedia. Quantitative analysis revealed that accuracy of drug information in Wikipedia was 99.7%±0.2% when compared to the textbook data. The overall completeness of drug information in Wikipedia was 83.8±1.5% (p<0.001). Completeness varied in-between categories, and was lowest in the category “pharmacokinetics” (68.0%±4.2%; p<0.001) and highest in the category “indication” (91.3%±2.0%) when compared to the textbook data overlap. Similar results were obtained for the English language version of Wikipedia. Of the drug information missing in Wikipedia, 62.5% was rated as didactically non-relevant in a qualitative re-evaluation study. Drug articles in Wikipedia had an average of 14.6±1.6 references and 262.8±37.4 edits performed by 142.7±17.6 editors. Both Wikipedia and textbooks samples had comparable, low readability. Our study suggests that Wikipedia is an accurate and comprehensive source of drug-related information for undergraduate medical education.