Regional Specification of the Xenopus Lateral Plate Mesoderm

@font-face { font-family: Times ; }@font-face { font-family: Cambria ; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: Times New Roman ; }div.Section1 { page: Section1; } Successful patterning of the embryo, from establishing the three primary axes to the regional specification of tissue progenitors is essential to generating a viable embryo. The three germ layers in the early embryo undergo patterning through slightly different mechanisms. The tissue of interest to this study is the lateral plate mesoderm (LPM), which will give rise to the lineages of the cardiovascular system and is essential for regional specification of adjacent germ layers. However, little is known about how the LPM itself undergoes regional specification and attains its intitial patterning after gastrulation. Here, I will demonstrate that a complex pattern of gene expression exists across the entire LPM shortly after gastrulation, much earlier than previously recognized. Furthermore, I will use molecular techniques to elucidate the signalling factors involved in the early patterning and regional specification the LPM. I hypothesize that both the retinoic acid (RA) and Fibroblast Growth Factor (FGF) signalling pathways are involved in the LPM regional specification in the neurula stage embryo. Through the use of exogenous modulators of the RA pathway, I will show that RA signalling is essential for patterning the anterior-dorsal and middle LPM domains. Secondly, by addition of a synthetic FGF receptor inhibitor I will demonstrate that FGF signalling is essential for establishing the anterior-ventral and posterior domains of the LPM and functions antagonistically to the RA pathway. I will also show that altering the activity of either of these two signalling pathways affects the specification of the early cardiovascular progenitors, particularly the cardiac and endothelial lineages. Finally I will provide preliminary evidence that one of the early LPM marker genes, Hand1, is necessary for normal cardiovascular development and thus provide a link between the early LPM pattern and later organogenesis. A thorough understanding of the mechanisms behind specifying embryonic lineages is of vital importance for basic biological knowledge, as well as for providing a basis for the emerging field of regenerative medicine, whereby researchers are attempting to generate organ progenitors in vivo to be used for cell therapies

Wochenbericht POS504

Wochenbericht zur Forschungsreise POS504 mit F/S Poseidon (27.08.-09.09.

Hydroacoustic and geochemical traces of marine gas seepage in the North Sea

Methane is the second most important anthropogenic greenhouse gas on Earth and contributes considerably to global radiative forcing. The last IPCC assessment report 2007 assigns geological methane emissions as a significant source. This thesis therefore concentrates on the quantity and atmospheric implications of methane emissions from the seabed of the North Sea. Sampling of marine seepage is challenging compared to readily accessible terrestrial sites; thus marine seepage sites have scarcely been observed or even yet discovered. Moreover, in terms of atmospheric contribution, the fate of methane after ebullition into the water column is usually not considered. Hydroacoustic systems have proven to be very efficient remote sensing tools for gas seepage analysis even in water depth greater than 2000 m. Technical progress led to much higher remote sensing potential by means of modern multibeam applications for gas bubbles detection in the water column. However, to be effective, these novel multibeam systems require new methods for data analysis. This thesis firstly demonstrates the application of multibeam systems as efficient gas bubble remote sensing tools. Therefore an anthropogenic blowout site was mapped using a multibeam sonar. The advantage of multibeam technology compared to singlebeam is increased efficiency due to larger coverage than singlebeam systems, three dimensional plume mapping, and exact localization of gas sources. Moreover the deployment of the multibeam prototype GasQuant is examined, which is an adapted sounder specifically designed for in situ gas bubble detection. GasQuant was deployed for several days within a gas seep field in the Central North Sea (Tommeliten). Aside from minor system adaptations, major effort was spent to handle the non-standard large datasets by means of various data processing and visualization routines. Taking into account the surrounding tidal current flow field, unique data patterns were extracted to unambiguously detect gas bubbles in the water column. Thus, a total of 52 single seep holes were localized and characterized with respect to their tempo-spatial variability. Recently, water column scanning multibeam mapping systems entered the market. Due to their huge amount of data output, manual processing is no longer feasible. Thus, a generic algorithm for the detection of rising gas bubbles in multibeam data was developed that accounts for the current tidal flow field for detection issues (Appendix A). Incorporation of other disciplines such as geochemistry and oceanography allowed for a methane gas source strength estimate of the Tommeliten gas seepage field in the North Sea. Combined acoustic mapping and in situ sampling revealed a source strength of ~0.8-4.8*106 mol/yr – a considerable quantity compared to prominent gas seep sites around the world (e.g. ~1*106 mol/yr at Vodyanitskii mud volcano, Black Sea; 2.19*106 mol/yr at North Hydrate Ridge offshore Oregon). Obviously previous studies have underestimated the area of active venting at Tommeliten. By modeling gas bubble dissolution and geochemical sampling it was found that the majority of bubble-mediated methane at Tommeliten already dissolves in the ‘deep’ water between the 70 m release depth and 40 m. Thus the methane is trapped below the upper-well mixed summer layer, from which it would readily be degassed by air-sea exchange processes. Given the heavy storm activity during winter, research cruises into the North Sea preferentially take place during the summer, where low atmospheric outgassing/emissions from seabed methane is expected due to stratification. However, considering the distinct hydrographic seasonal cycle of the North Sea, quantitative transport of seepage methane into the atmosphere seems likely during winter after fall mixing. This seasonal bias is not only constrained to the study site, but relevant for the entire Central and Northern North Sea as well as many mid-latitude shallow shelf sea waters showing temporal stratification

Well-posedness in smooth function spaces for the moving-boundary 1-D compressible Euler equations in physical vacuum

The free-boundary compressible 1-D Euler equations with moving physical vacuum boundary are a system of hyperbolic conservation laws which are both characteristic and degenerate. The physical vacuum singularity (or rate-of-degeneracy) requires the sound speed $c= \gamma \rho^{\gamma -1}$ to scale as the square-root of the distance to the vacuum boundary, and has attracted a great deal of attention in recent years. We establish the existence of unique solutions to this system on a short time-interval, which are smooth (in Sobolev spaces) all the way to the moving boundary. The proof is founded on a new higher-order Hardy-type inequality in conjunction with an approximation of the Euler equations consisting of a particular degenerate parabolic regularization. Our regular solutions can be viewed as degenerate viscosity solutions.Comment: 27 page

A rigorous formulation of the cosmological Newtonian limit without averaging

We prove the existence of a large class of one-parameter families of cosmological solutions to the Einstein-Euler equations that have a Newtonian limit. This class includes solutions that represent a finite, but otherwise arbitrary, number of compact fluid bodies. These solutions provide exact cosmological models that admit Newtonian limits but, are not, either implicitly or explicitly, averaged

Beyond Bathymetry: Water Column Imaging with Multibeam Echo Sounder Systems

Echo sounder systems represent powerful tools not only to determine the seafloor depth, but also to investigate the water column. The most prominent fields of hydro acoustic water column applications include fish shoal detection and biomass assessments, target detection for military purposes, oil and gas leakage detection, and suspension matter analyses. Multibeam echo sounder systems (MBES) – so far primarily used for bathymetric measurements – are introduced in this study for demonstrating their water column analyses capabilities that become more and more available due to most recent computer power and mass storage advances. Some environmental data are presented in this study showing gas release from the seabed, fish shoals, zooplankton and oceanographic layers to highlight multibeam water column potentials. Moreover multibeam water column assessments are suggested to be valuable for the hydrographer as a supporting tool potentially useful for mitigating MBES survey related conflicts