In vivo Analysis of Choroid Plexus Morphogenesis in Zebrafish

BACKGROUND: The choroid plexus (ChP), a component of the blood-brain barrier (BBB), produces the cerebrospinal fluid (CSF) and as a result plays a role in (i) protecting and nurturing the brain as well as (ii) in coordinating neuronal migration during neurodevelopment. Until now ChP development was not analyzed in living vertebrates due to technical problems. METHODOLOGY/PRINCIPAL FINDINGS: We have analyzed the formation of the fourth ventricle ChP of zebrafish in the GFP-tagged enhancer trap transgenic line SqET33-E20 (Gateways) by a combination of in vivo imaging, histology and mutant analysis. This process includes the formation of the tela choroidea (TC), the recruitment of cells from rhombic lips and, finally, the coalescence of TC resulting in formation of ChP. In Notch-deficient mib mutants the first phase of this process is affected with premature GFP expression, deficient cell recruitment into TC and abnormal patterning of ChP. In Hedgehog-deficient smu mutants the second phase of the ChP morphogenesis lacks cell recruitment and TC cells undergo apoptosis. CONCLUSIONS/SIGNIFICANCE: This study is the first to demonstrate the formation of ChP in vivo revealing a role of Notch and Hedgehog signalling pathways during different developmental phases of this process

Phase Diagram of the B–BN System at Pressures up to 24 GPa: Experimental Study and Thermodynamic Analysis

Phase relations in the B–BN system have been studied ex situ and in situ at pressures 2–20 GPa and temperatures up to 2800 K. The evolution of topology of the B–BN phase diagram has been investigated up to 24 GPa using models of phenomenological thermodynamics with interaction parameters derived from our experimental data on phase equilibria at high pressures and high temperatures. There are two thermodynamically stable boron subnitrides in the system i.e. B$_{13}$N$_2$ and B$_{50}$N$_2$. Above 16.5 GPa, the $B_{50}N_2 ⇄ L + B_{13}N_2$ peritectic reaction transforms to the solid-phase reaction of $B_{50}N_2$ decomposition into tetragonal boron $(t′-B_{52})$ and B$_{13}$N$_2$, while the incongruent type of B$_{13}$N$_2$ melting changes to the congruent type only above 23.5 GPa. The constructed phase diagram provides fundamentals for directed high-pressure synthesis of superhard phases in the B–BN system

Kinetics of cBN crystallization in the Li3N−BN\mathrm{Li_{3}N-BN} system at 6.6 GPa

Kinetics of cBN crystallization from the Li3N-BN melt being in equilibrium with hBN has been studied in situ at 6.6 GPa in the 1720–1820 K range using diffraction of synchrotron radiation. The process under consideration has been found to have the activation energy of 115 ± 5 kJ mol−1 and to be controlled by BN diffusion in the melt. Kinetics data might be best fitted by a model that assumes an instantaneous nucleation in the initial stage of crystallization and nucleation at constant rate when hBN-to-cBN conversion degree is higher than 0.2. Using the model or regular solutions, the maximum solubilities of hBN and cBN in the melt of the Li3N-BN system were calculated, which allowed the BN diffusion coefficient in the melt at 6.6 GPa and 1770 K to be evaluated at (3 ± 1) × 10−7cm2 s−1

On Nucleation of Cubic Boron Nitride in the BN−MgB2\mathrm{BN−MgB_2} System

X-ray powder diffraction with synchrotron radiation was used to study the formation of cubic boron nitride (cBN) in the MgB2−BN system at pressures to 6.8 GPa and temperatures to 2000 K. For the formation of cBN, when it crystallizes from a BN solution in the melt of the system under study, the threshold pressure (4.5 ± 0.1 GPa) and low-temperature boundary (T (K) = 1633 − 9.2p (GPa)) have been established. We have calculated pressure and temperature dependences of the rate of cBN nucleation and have found that the position of the high-temperature boundary of the p,T region of the cBN crystallization is specified by the nucleation of the cubic phase. The existence of the threshold pressure of cBN crystallization is dictated by the strong pressure dependence of the nucleation rate. It is just this dependence that is responsible for the fact that the region of the cBN spontaneous crystallization is well off the hBN ⇆ cBN equilibrium line by several hundred degrees

Refined Phase Diagram of Boron Nitride

The equilibrium phase diagram of boron nitride thermodynamically calculated by Solozhenko in 1988 has been now refined on the basis of new experimental data on BN melting and extrapolation of heat capacities of BN polymorphs into high-temperature region using the adapted pseudo-Debye model. As compared with the above diagram, the hBN ⇆ cBN equilibrium line is displaced by 60 K toward higher temperatures. The hBN−cBN−L triple point has been calculated to be at 3480 ± 10 K and 5.9 ± 0.1 GPa, while the hBN−L−V triple point is at T = 3400 ± 20 K and p = 400 ± 20 Pa, which indicates that the region of thermodynamic stability of vapor in the BN phase diagram is extremely small. It has been found that the slope of the cBN melting curve is positive whereas the slope of hBN melting curve varies from positive between ambient pressure and 3.4 GPa to negative at higher pressures

Phase Equilibria in the B–BN–B2O3\mathrm{B–BN–B_{2}O_{3}} System at 5 GPa

Phase equilibria in the B–BN–B$_{2}$O$_{3}$ ternary system at pressures up to 5 GPa have been studied by in situ probing with synchrotron X-ray powder diffraction, microscopic and X-ray diffraction characterization of recovered samples, and thermodynamic analysis. The phase diagram of the system has been constructed by combining the previously reported data for binary subsystems and a conventional phenomenological model describing ternary interactions. The interaction parameter of the model of the ternary liquid phase has been determined by adjustment of experimental melting points to the calculated monovariant eutectic curve. The phase diagram is characterized by two ternary eutectics, one ternary transition-type equilibrium, and the maximum in the monovariant eutectic curve

Mg–C System up to 20 GPa: Its Phase Diagram and Stable Magnesium Carbides

International audienceThe phase diagram of the Mg−C system has been constructed up to 20 GPa and ∼4000 K based on complementary Thermo-Calc simulations and experimental data obtained in both ex situ and in situ experiments using X-ray diffraction with synchrotron radiation. Three high-pressure magnesium carbides, namely, β-Mg 2 C 3 , its high-temperature form γ-Mg 2 C 3 , and antifluorite Mg 2 C, have p−T domains of thermodynamic stability. At the same time, the carbides accessible by ambient-pressure synthesis, α-Mg 2 C 3 and MgC 2 , are either metastable or unstable, depending on the temperature, at least up to 20 GPa. Experimental observations show that at ambient conditions, all carbides are metastable and remain unchanged at least for years