Ciliation and gene expression distinguish between node and posterior notochord in the mammalian embryo

The mammalian node, the functional equivalent of the frog dorsal blastoporal lip (Spemann's organizer), was originally described by Viktor Hensen in 1876 in the rabbit embryo as a mass of cells at the anterior end of the primitive streak. Today, the term "node" is commonly used to describe a bilaminar epithelial groove presenting itself as an indentation or "pit" at the distal tip of the mouse egg cylinder, and cilia on its ventral side are held responsible for molecular laterality (left-right) determination. We find that Hensen's node in the rabbit is devoid of cilia, and that ciliated cells are restricted to the notochordal plate, which emerges from the node rostrally. In a comparative approach, we use the organizer marker gene Goosecoid (Gsc) to show that a region of densely packed epithelium-like cells at the anterior end of the primitive streak represents the node in mouse and rabbit and is covered ventrally by a hypoblast (termed "visceral endoderm" in the mouse). Expression of Nodal, a gene intricately involved in the determination of vertebrate laterality, delineates the wide plate-like posterior segment of the notochord in the rabbit and mouse, which in the latter is represented by the indentation frequently termed "the node." Similarly characteristic ciliation and nodal expression exists in Xenopus neurula embryos in the gastrocoel roof plate (GRP), i.e., at the posterior end of the notochord anterior to the blastoporal lip. Our data suggest that (1) a posterior segment of the notochord, here termed PNC (for posterior notochord), is characterized by features known to be involved in laterality determination, (2) the GRP in Xenopus is equivalent to the mammalian PNC, and (3) the mammalian node as defined by organizer gene expression is devoid of cilia and most likely not directly involved in laterality determination.     

Wnt signaling mediates regional specification in the vertebrate face

At early stages of development, the faces of vertebrate embryos look remarkably similar, yet within a very short timeframe they adopt species-specific facial characteristics. What are the mechanisms underlying this regional specification of the vertebrate face? Using transgenic Wnt reporter embryos we found a highly conserved pattern of Wnt responsiveness in the developing mouse face that later corresponded to derivatives of the frontonasal and maxillary prominences. We explored the consequences of disrupting Wnt signaling, first using a genetic approach. Mice carrying compound null mutations in the nuclear mediators Lef1 and Tcf4 exhibited radically altered facial features that culminated in a hyperteloric appearance and a foreshortened midface. We also used a biochemical approach to perturb Wnt signaling and found that in utero delivery of a Wnt antagonist, Dkk1, produced similar midfacial malformations. We tested the hypothesis that Wnt signaling is an evolutionarily conserved mechanism controlling facial morphogenesis by determining the pattern of Wnt responsiveness in avian faces, and then by evaluating the consequences of Wnt inhibition in the chick face. Collectively, these data elucidate a new role for Wnt signaling in regional specification of the vertebrate face, and suggest possible mechanisms whereby species-specific facial features are generated.     

Flow behaviour of a POSS biopolymer solution

A non-biodegradable polyhedral oligomeric silsesquioxane (POSS) nanocomposite biopolymer has been developed for fabrication of medical devices and for tissue engineering human organs. The polymer in solution, containing 2 wt% of POSS, has been synthesized, characterized and investigated to determine its key rheological properties. Thus, the variation of shear stress and viscosity as a function of shear rate has been determined at ambient temperature to estimate yield stress and the index of pseudoplasticity, respectively. The temperature dependence of viscosity and the effect of ageing on the viscosity of the polymer have also been investigated. Results are compared with those of a conventional polycarbonate urethane (PCU) polymer solution. The POSS-PCU polymer solution shows near-Newtonian behaviour in the shear rate range to 1000 s(-1), having an apparent viscosity of approximately 3000 mPa s and a pseudoplasticity index of 0.90, decreasing slightly as the polymer solution is aged over 9 months. The temperature dependence of viscosity of the POSS polymer is extremely low and does not change with ageing but the yield strength increases from 2.7 Pa to 8.3 Pa.     

Male germ cell expression of the PAS domain kinase PASKIN and its novel target eukaryotic translation elongation factor eEF1A1.

PASKIN links energy flux and protein synthesis in yeast, regulates glycogen synthesis in mammals, and has been implicated in glucose-stimulated insulin production in pancreatic beta-cells. Using newly generated monoclonal antibodies, PASKIN was localized in the nuclei of human testis germ cells and in the midpiece of human sperm tails. A speckle-like nuclear pattern was observed for endogenous PASKIN in HeLa cells in addition to its cytoplasmic localization. By yeast two-hybrid screening, we identified the multifunctional eukaryotic translation elongation factor eEF1A1 as a novel interaction partner of PASKIN. This interaction was mapped to the PAS A and kinase domains of PASKIN and to the C-terminus of eEF1A1 using mammalian two-hybrid and GST pull-down assays. Kinase assays, mass spectrometry and site-directed mutagenesis revealed PASKIN auto-phosphorylation as well as eEF1A1 target phosphorylation mainly but not exclusively at Thr432. Wild-type but not kinase-inactive PASKIN increased the in vitro translation of a reporter cRNA. Whereas eEF1A1 did not localize to the nucleus, it co-localizes with PASKIN to the cytoplasm of HeLa cells. The two proteins also showed a remarkably similar localization in the midpiece of the sperm tail. These data suggest regulation of eEF1A1 by PASKIN-dependent phosphorylation in somatic as well as in sperm cells.     

Pulmonary vasodilation by acetazolamide during hypoxia is unrelated to carbonic anhydrase inhibition

Acute hypoxic pulmonary vasoconstriction can be inhibited by high doses of the carbonic anhydrase inhibitor acetazolamide. This study aimed to determine whether acetazolamide is effective at dosing relevant to human use at high altitude and to investigate whether its efficacy against hypoxic pulmonary vasoconstriction is dependent on carbonic anhydrase inhibition by testing other potent heterocyclic sulfonamide carbonic anhydrase inhibitors. Six conscious dogs were studied in five protocols: 1) controls, 2) low-dose intravenous acetazolamide (2 mg.kg(-1).h(-1)), 3) oral acetazolamide (5 mg/kg), 4) benzolamide, a membrane-impermeant inhibitor, and 5) ethoxzolamide, a membrane-permeant inhibitor. In all protocols, unanesthetized dogs breathed spontaneously during the first hour (normoxia) and then breathed 9-10% O(2) for the next 2 h. Arterial oxygen tension ranged between 35 and 39 mmHg during hypoxia in all protocols. In controls, mean pulmonary artery pressure increased by 8 mmHg and pulmonary vascular resistance by 200 dyn.s.cm(-5) (P <0.05). With intravenous acetazolamide, mean pulmonary artery pressure and pulmonary vascular resistance remained unchanged during hypoxia. With oral acetazolamide, mean pulmonary artery pressure increased by 5 mmHg (P < 0.05), but pulmonary vascular resistance did not change during hypoxia. With benzolamide and ethoxzolamide, mean pulmonary artery pressure increased by 6-7 mmHg and pulmonary vascular resistance by 150-200 dyn.s.cm(-5) during hypoxia (P < 0.05). Low-dose acetazolamide is effective against acute hypoxic pulmonary vasoconstriction in vivo. The lack of effect with two other potent carbonic anhydrase inhibitors suggests that carbonic anhydrase is not involved in the mediation of hypoxic pulmonary vasoconstriction and that acetazolamide acts on a different receptor or channel.     

Extralymphatic virus sanctuaries as a consequence of potent T-cell activation

T helper cells can support the functions of CD8(+) T cells against persistently infecting viruses such as murine lymphocytic choriomeningitis virus (LCMV), cytomegalovirus, hepatitis C virus and HIV. These viruses often resist complete elimination and remain detectable at sanctuary sites, such as the kidneys and other extralymphatic organs. The mechanisms underlying this persistence are not well understood. Here we show that mice with potent virus-specific T-cell responses have reduced levels and delayed formation of neutralizing antibodies, and these mice fail to clear LCMV from extralymphatic epithelia. Transfer of virus-specific B cells but not virus-specific T cells augmented virus clearance from persistent sites. Virus elimination from the kidneys was associated with the formation of IgG deposits in the interstitial space, presumably from kidney-infiltrating B cells. CD8(+) T cells in the kidneys of mice that did not clear virus from this site were activated but showed evidence of exhaustion. Thus, we conclude that in this model of infection, site-specific virus persistence develops as a consequence of potent immune activation coupled with reductions in virus-specific neutralizing antibodies. Our results suggest that sanctuary-site formation depends both on organ anatomy and on the induction of different adaptive immune effector mechanisms. Boosting T-cell responses alone may not reduce virus persistence.     

Lipidomics of Thalassiosira pseudonana as a function of valve SDV synthesis

Journal of Applied Phycology - Silica polycondensation occurring in diatom organelles called silica deposition vesicles (SDVs) leads to valve and girdle band formation to complete the biosilica...     

Osmoprotective effect of ubiquinone in lipid vesicles modelling the E. coli plasma membrane

Bacteria need to be able to adapt to sudden changes in their environment, including drastic changes in the surrounding osmolarity. As part of this adaptation, the cells adjust the composition of their cytoplasmic membrane. Recent studies have shown that ubiquinones, lipid soluble molecules involved in cell respiration, are overproduced by bacteria grown in hyperosmotic conditions and it is thus believed that these molecules can provide with osmoprotection. Hereby we explore the mechanisms behind these observations. Liposomes with a lipid headgroup composition mimicking that of the cytoplasmic membrane of E. coli are used as suitable models. The effect of ubiquinone-10 (Q10) on water transport across the membranes is characterized using a custom developed fluorescence-based experimental approach to simultaneously determine the membrane permeability coefficient and estimate the elastic resistance of the membrane towards deformation. It is shown that both parameters are affected by the presence of ubiquinone-10. Solanesol, a molecule similar to Q10 but lacking the quinone headgroup, also provides with osmoprotection although it only improves the resistance of the membrane against deformation. The fluorescence experiments are complemented by cryogenic transmission electron microscopy studies showing that the E. coli membrane mimics tend to flatten into spheroid oblate structures when osmotically stressed, suggesting the possibility of lipid segregation. In agreement with its proposed osmoprotective role, the flattening process is hindered by the presence of Q10.     

Response of maize biomass and soil water fluxes on elevated CO2 and drought—From field experiments to process‐based simulations

The rising concentration of atmospheric carbon dioxide (CO₂) is known to increase the total aboveground biomass of several C3 crops, whereas C4 crops are reported to be hardly affected when water supply is sufficient. However, a free‐air carbon enrichment (FACE) experiment in Braunschweig, Germany, in 2007 and 2008 resulted in a 25% increased biomass of the C4 crop maize under restricted water conditions and elevated CO₂ (550 ppm). To project future yields of maize under climate change, an accurate representation of the effects of eCO₂ and drought on biomass and soil water conditions is essential. Current crop growth models reveal limitations in simulations of maize biomass under eCO₂ and limited water supply. We use the coupled process‐based hydrological‐plant growth model Catchment Modeling Framework‐Plant growth Modeling Framework to overcome this limitation. We apply the coupled model to the maize‐based FACE experiment in Braunschweig that provides robust data for the investigation of combined CO₂ and drought effects. We approve hypothesis I that CO₂ enrichment has a small direct‐fertilizing effect with regard to the total aboveground biomass of maize and hypothesis II that CO₂ enrichment decreases water stress and leads to higher yields of maize under restricted water conditions. Hypothesis III could partly be approved showing that CO₂ enrichment decreases the transpiration of maize, but does not raise soil moisture, while increasing evaporation. We emphasize the importance of plant‐specific CO₂ response factors derived by use of comprehensive FACE data. By now, only one FACE experiment on maize is accomplished applying different water levels. For the rigorous testing of plant growth models and their applicability in climate change studies, we call for datasets that go beyond single criteria (only yield response) and single effects (only elevated CO₂).     

Identification of Embryonic Neural Plate Border Stem Cells and Their Generation by Direct Reprogramming from Adult Human Blood Cells

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