Probing disorders of the nervous system using reprogramming approaches

The groundbreaking technologies of induced pluripotency and lineage conversion have generated a genuine opportunity to address fundamental aspects of the diseases that affect the nervous system. These approaches have granted us unrestricted access to the brain and spinal cord of patients and have allowed for the study of disease in the context of human cells, expressing physiological levels of proteins and under each patient's unique genetic constellation. Along with this unprecedented opportunity have come significant challenges, particularly in relation to patient variability, experimental design and data interpretation. Nevertheless, significant progress has been achieved over the past few years both in our ability to create the various neural subtypes that comprise the nervous system and in our efforts to develop cellular models of disease that recapitulate clinical findings identified in patients. In this Review, we present tables listing the various human neural cell types that can be generated and the neurological disease modeling studies that have been reported, describe the current state of the field, highlight important breakthroughs and discuss the next steps and future challenges.     

Soil structural aspects of decomposition of organic matter by micro-organisms

Soil architecture is the dominant control over microbially mediated decomposition processes in terrestrial ecosystems. Organic matter is physically protected in soil so that large amounts of well-decomposable compounds can be found in the vicinity of largely starving microbial populations. Among the mechanisms proposed to explain the phenomena of physical protection in soil are adsorption of organics on inorganic clay surfaces and entrapment of materials in aggregates or in places inaccessible to microbes. Indirect evidence for the existence of physical protection in soil is provided by the occurrence of a burst of microbial activity and related increased decomposition rates following disruption of soil structures, either by natural processes such as the remoistening of a dried soil or by human activities such as ploughing. In contrast, soil compaction has only little effect on the transformation of ¹⁴C-glucose. Another mechanism of control by soil structure and texture on decomposition in terrestrial ecosystems is through their impact on microbial turnover processes. The microbial population is not only the main biological agent of decomposition in soil, it is also an important, albeit small, pool through which most of the organic matter in soil passes. Estimates on the relative importance of different mechanisms controlling decomposition in soil could be derived from results of combined tracer and modelling studies. However, suitable methodology to quantify the relation between soil structure and biological processes as a function of different types and conditions of soils is still lacking.     

Systematics of Pseudorchis albida s.l. (Orchidaceae) in Europe and North America

In Scandinavia Pseudorchis albida (Orchidaceae)usually divided into the lowland and subalpine P. albida s.s. and the more or less alpine P. straminea. There have been some uncertainties and conflicting views concerning die taxonomic treatment of diese taxa. To address this issue, herbarium specimens of P. albida s.l. were studied for variation in morphological characters. A small-scale population study approach was used, as herbarium sheets with two or three plants were used as population samples. Canonical Variates Analysis (CVA) indicated a distinction between taxa in population means, corresponding to P. albida s.s. and P. straminea , respectively. Principal Components Analysis (PCA), however, revealed an overlap between individuals of the two taxa. The PGA analysis, furthermore, revealed that the overlap was considerably larger in material from Central Europe man in material from Fennoscandia. Student t -tests on separate characters confirmed the picture, wim more characters significantly different in Fennoscandian than in Central European material. Furthermore, a Tukey-Kramer test revealed that there were small differences between regional populations of P. albida s.s. , while there were several significant differences in single characters between the Norm American regional population of P. straminea , as compared with the Central European and Fennoscandian regional populations. In Central Europe there is no clear separation between taxa, while in Fennoscandia the taxa are more clearly separated. This probably means that there is a difference in the time of establishment in the different regions. The author suggests a distinction of taxa at the subspecies level, and argues that the clear distinction seen in Fennoscandian material is due to separate immigration histories for die two subspecies into Fennoscandia after the last period of glaciation.     

Phosphorylation of elF-4E and initiation of protein synthesis in P19 embryonal carcinoma cells

Mitogenic stimulation of protein synthesis is accompanied by an increase in elF-4E phosphorylation. The effect on protein synthesis by induction of differentiation is less well known. We treated P19 embryonal carcinoma cells with the differentiating agent retinoic acid and found that protein synthesis increased during the first hour of addition. However, the phosphorylation state, as well as the turnover of phosphate on elF-4E, remained unchanged. Apparently, the change in protein synthesis after RA addition is regulated by another mechanism than elF-4E phosphorylation. By using P19 cells overexpressing the EGF receptor, we show that the signal transduction pathway that leads to phosphorylation of elF-4E is present in P19 cells; the EGF-induced change in phosphorylation of elF-4E in these cells is likely to be regulated by a change in elF-4E phosphatase activity. These results suggest that the onset of retinoic acid-induced differentiation is triggered by a signal transduction pathway which involves changes in protein synthesis, but not elF-4E phosphorylation. © 1995 Wiley-Liss, Inc.     

The role of lipid second messengers in aldosterone synthesis and secretion

Second messengers are small rapidly diffusing molecules or ions that relay signals between receptors and effector proteins to produce a physiological effect. Lipid messengers constitute one of the four major classes of second messengers. The hydrolysis of two main classes of lipids, glycerophospholipids and sphingolipids, generate parallel profiles of lipid second messengers: phosphatidic acid (PA), diacylglycerol (DAG), and lysophosphatidic acid versus ceramide, ceramide-1-phosphate, sphingosine, and sphingosine-1-phosphate, respectively. In this review, we examine the mechanisms by which these lipid second messengers modulate aldosterone production at multiple levels. Aldosterone is a mineralocorticoid hormone responsible for maintaining fluid volume, electrolyte balance, and blood pressure homeostasis. Primary aldosteronism is a frequent endocrine cause of secondary hypertension. A thorough understanding of the signaling events regulating aldosterone biosynthesis may lead to the identification of novel therapeutic targets. The cumulative evidence in this literature emphasizes the critical roles of PA, DAG, and sphingolipid metabolites in aldosterone synthesis and secretion. However, it also highlights the gaps in our knowledge, such as the preference for phospholipase D-generated PA or DAG, as well as the need for further investigation to elucidate the precise mechanisms by which these lipid second messengers regulate optimal aldosterone production.     

Heterotrimeric G Proteins Directly Regulate MMP14/Membrane Type-1 Matrix Metalloprotease: A NOVEL MECHANISM FOR GPCR-EGFR TRANSACTIVATION*

Agonist stimulation of G protein-coupled receptors (GPCRs) can transactivate epidermal growth factor receptors (EGFRs), but the precise mechanisms for this transactivation have not been defined. Key to this process is the protease-mediated “shedding” of membrane-tethered ligands, which then activate EGFRs. The specific proteases and the events involved in GPCR-EGFR transactivation are not fully understood. We have tested the hypothesis that transactivation can occur by a membrane-delimited process: direct increase in the activity of membrane type-1 matrix metalloprotease (MMP14, MT1-MMP) by heterotrimeric G proteins, and in turn, the generation of heparin-binding epidermal growth factor (HB-EGF) and activation of EGFR. Using membranes prepared from adult rat cardiac myocytes and fibroblasts, we found that MMP14 activity is increased by angiotensin II, phenylephrine, GTP, and guanosine 5′-O-[γ-thio]triphosphate (GTPγS). MMP14 activation by GTPγS occurs in a concentration- and time-dependent manner, does not occur in response to GMP or adenosine 5′-[γ-thio]triphosphate (ATPγS), and is not blunted by inhibitors of Src, PKC, phospholipase C (PLC), PI3K, or soluble MMPs. This activation is specific to MMP14 as it is inhibited by a specific MMP14 peptide inhibitor and siRNA knockdown. MMP14 activation by GTPγS is pertussis toxin-sensitive. A role for heterotrimeric G protein βγ subunits was shown by using the Gβγ inhibitor gallein and the direct activation of recombinant MMP14 by purified βγ subunits. GTPγS-stimulated activation of MMP14 also results in membrane release of HB-EGF and the activation of EGFR. These results define a previously unrecognized, membrane-delimited mechanism for EGFR transactivation via direct G protein activation of MMP14 and identify MMP14 as a heterotrimeric G protein-regulated effector.     

Divergence in germination traits among arctic and alpine populations of <Emphasis Type="Italic">Koenigia islandica</Emphasis>: light requirements

Light is known to regulate conservative germination strategies and the formation of seed banks. Although these strategies are crucial to survival in tundra environments—especially for annuals—light requirements for germination in arctic–alpine species are seldom investigated. Furthermore, environmental differences between arctic and alpine regions are expected to lead to evolutionary divergence among conspecific populations in seed germination strategies. In this study, we report important differences in germination light requirements among six arctic and alpine populations of the annual Koenigia islandica. Light had little effect on germination of the seeds from Iqaluit (Nunavut, Canada), Yukon (Canada), and Jasper (Alberta, Canada), whereas the seeds from the most severe climates, Svalbard (Norway) and Colorado (USA), had strong light requirements. Stratification of the seeds had little influence on their germination light requirements, with the exception of the population from Dovre (Norway), in which it induced a strong light requirement. Possible adaptive explanations and some implications of these observed germination patterns are discussed.