Mechanism of carrier-induced ferromagnetism in magnetic semiconductors

Taking into account both random impurity distribution and thermal fluctuations of localized spins, we have performed a model calculation for the carrier (hole) state in Ga$_{1-x}$Mn$_x$As by using the coherent potential approximation (CPA). The result reveals that a {\it p}-hole in the band tail of Ga$_{1-x}$Mn$_x$As is not like a free carrier but is rather virtually bounded to impurity sites. The carrier spin strongly couples to the localized {\it d} spins on Mn ions. The hopping of the carrier among Mn sites causes the ferromagnetic ordering of the localized spins through the double-exchange mechanism. The Curie temperature obtained by using conventional parameters agrees well with the experimental result.Comment: 7 pages, 4 figure

Spin dynamics and spin freezing in the triangular lattice antiferromagnets FeGa2S4 and NiGa2S4

Magnetic susceptibility and muon spin relaxation (muSR) experiments have been carried out on the quasi-2D triangular-lattice spin S = 2 antiferromagnet FeGa2S4. The muSR data indicate a sharp onset of a frozen or nearly-frozen spin state at T* = 31(2) K, twice the spin-glass-like freezing temperature T_f = 16(1) K. The susceptibility becomes field dependent below T*, but no sharp anomaly is observed in any bulk property. A similar transition is observed in muSR data from the spin-1 isomorph NiGa2S4. In both compounds the dynamic muon spin relaxation rate lambda_d(T) above T* agrees well with a calculation of spin-lattice relaxation by Chubukov, Sachdev, and Senthil in the renormalized classical regime of a 2D frustrated quantum antiferromagnet. There is no firm evidence for other mechanisms. At low temperatures lambda_d(T) becomes temperature independent in both compounds, indicating persistence of spin dynamics. Scaling of lambda_d(T) between the two compounds is observed from ~T_f to ~1.5T*. Although the muSR data by themselves cannot exclude a truly static spin component below T*, together with the susceptibility data they are consistent with a slowly-fluctuating "spin gel" regime between T_f and T*. Such a regime and the absence of a divergence in lambda_d(T) at T* are features of two unconventional mechanisms: (1) binding/unbinding of Z_2 vortex excitations, and (2) impurity spins in a nonmagnetic spin-nematic ground state. The absence of a sharp anomaly or history dependence at T* in the susceptibility of FeGa2S4, and the weakness of such phenomena in NiGa2S4, strongly suggest transitions to low-temperature phases with unconventional dynamics.Comment: 13 pages, 6 figures, accepted for publication in Physical Review

Gene expression atlas of fruit ripening and transcriptome assembly from RNA-seq data in octoploid strawberry (Fragaria × ananassa)

RNA-seq has been used to perform global expression analysis of the achene and the receptacle at four stages of fruit ripening, and of the roots and leaves of strawberry (Fragaria × ananassa). About 967 million reads and 191 Gb of sequence were produced, using Illumina sequencing. Mapping the reads in the related genome of the wild diploid Fragaria vesca revealed differences between the achene and receptacle development program, and reinforced the role played by ethylene in the ripening receptacle. For the strawberry transcriptome assembly, a de novo strategy was followed, generating separate assemblies for each of the ten tissues and stages sampled. The Trinity program was used for these assemblies, resulting in over 1.4 M isoforms. Filtering by a threshold of 0.3 FPKM, and doing Blastx (E-value < 1 e-30) against the UniProt database of plants reduced the number to 472,476 isoforms. Their assembly with the MIRA program (90% homology) resulted in 26,087 contigs. From these, 91.34 percent showed high homology to Fragaria vesca genes and 87.30 percent Fragaria iinumae (BlastN E-value < 1 e-100). Mapping back the reads on the MIRA contigs identified polymorphisms at nucleotide level, using FREEBAYES, as well as estimate their relative abundance in each sample

Biocompatibility, Inflammatory Response, and Recannalization Characteristics of Nonradioactive Resin Microspheres: Histological Findings

Intra-arterial radiotherapy with yttrium-90 microspheres (radioembolization) is a therapeutic procedure exclusively applied to the liver that allows the direct delivery of high-dose radiation to liver tumors, by means of endovascular catheters, selectively placed within the tumor vasculature. The aim of the study was to describe the distribution of spheres within the precapillaries, inflammatory response, and recannalization characteristics after embolization with nonradioactive resin microspheres in the kidney and liver. We performed a partial embolization of the liver and kidney vessels in nine white pigs. The left renal and left hepatic arteries were catheterized and filled with nonradioactive resin microspheres. Embolization was defined as the initiation of near-stasis of blood flow, rather than total occlusion of the vessels. The hepatic circulation was not isolated so that the effects of reflux of microspheres into stomach could be observed. Animals were sacrificed at 48 h, 4 weeks, and 8 weeks, and tissue samples from the kidney, liver, lung, and stomach evaluated. Microscopic evaluation revealed clusters of 10–30 microspheres (15–30 μm in diameter) in the small vessels of the kidney (the arciform arteries, vasa recti, and glomerular afferent vessels) and liver. Aggregates were associated with focal ischemia and mild vascular wall damage. Occlusion of the small vessels was associated with a mild perivascular inflammatory reaction. After filling of the left hepatic artery with microspheres, there was some evidence of arteriovenous shunting into the lungs, and one case of cholecystitis and one case of marked gastritis and ulceration at the site of arterial occlusion due to the presence of clusters of microspheres. Beyond 48 h, microspheres were progressively integrated into the vascular wall by phagocytosis and the lumen recannalized. Eight-week evaluation found that the perivascular inflammatory reaction was mild. Liver cell damage, bile duct injury, and portal space fibrosis were not observed. In conclusion, resin microspheres (15–30 μm diameter) trigger virtually no inflammatory response in target tissues (liver and kidney). Clusters rather than individual microspheres were associated with a mild to moderate perivascular inflammatory reaction. There was no evidence of either a prolonged inflammatory reaction or fibrosis in the liver parenchyma following recannalization

Vascular Endothelial Growth Factor Receptor-3 Directly Interacts with Phosphatidylinositol 3-Kinase to Regulate Lymphangiogenesis

Background Dysfunctional lymphatic vessel formation has been implicated in a number of pathological conditions including cancer metastasis, lymphedema, and impaired wound healing. The vascular endothelial growth factor (VEGF) family is a major regulator of lymphatic endothelial cell (LEC) function and lymphangiogenesis. Indeed, dissemination of malignant cells into the regional lymph nodes, a common occurrence in many cancers, is stimulated by VEGF family members. This effect is generally considered to be mediated via VEGFR-2 and VEGFR-3. However, the role of specific receptors and their downstream signaling pathways is not well understood. Methods and Results Here we delineate the VEGF-C/VEGF receptor (VEGFR)-3 signaling pathway in LECs and show that VEGF-C induces activation of PI3K/Akt and MEK/Erk. Furthermore, activation of PI3K/Akt by VEGF-C/VEGFR-3 resulted in phosphorylation of P70S6K, eNOS, PLCc1, and Erk1/2. Importantly, a direct interaction between PI3K and VEGFR-3 in LECs was demonstrated both in vitro and in clinical cancer specimens. This interaction was strongly associated with the presence of lymph node metastases in primary small cell carcinoma of the lung in clinical specimens. Blocking PI3K activity abolished VEGF-C-stimulated LEC tube formation and migration. Conclusions Our findings demonstrate that specific VEGFR-3 signaling pathways are activated in LECs by VEGF-C. The importance of PI3K in VEGF-C/VEGFR-3-mediated lymphangiogenesis provides a potential therapeutic target for the inhibition of lymphatic metastasis

A Mammalian Conserved Element Derived from SINE Displays Enhancer Properties Recapitulating Satb2 Expression in Early-Born Callosal Projection Neurons

Short interspersed repetitive elements (SINEs) are highly repeated sequences that account for a significant proportion of many eukaryotic genomes and are usually considered “junk DNA”. However, we previously discovered that many AmnSINE1 loci are evolutionarily conserved across mammalian genomes, suggesting that they may have acquired significant functions involved in controlling mammalian-specific traits. Notably, we identified the AS021 SINE locus, located 390 kbp upstream of Satb2. Using transgenic mice, we showed that this SINE displays specific enhancer activity in the developing cerebral cortex. The transcription factor Satb2 is expressed by cortical neurons extending axons through the corpus callosum and is a determinant of callosal versus subcortical projection. Mouse mutants reveal a crucial function for Sabt2 in corpus callosum formation. In this study, we compared the enhancer activity of the AS021 locus with Satb2 expression during telencephalic development in the mouse. First, we showed that the AS021 enhancer is specifically activated in early-born Satb2+ neurons. Second, we demonstrated that the activity of the AS021 enhancer recapitulates the expression of Satb2 at later embryonic and postnatal stages in deep-layer but not superficial-layer neurons, suggesting the possibility that the expression of Satb2 in these two subpopulations of cortical neurons is under genetically distinct transcriptional control. Third, we showed that the AS021 enhancer is activated in neurons projecting through the corpus callosum, as described for Satb2+ neurons. Notably, AS021 drives specific expression in axons crossing through the ventral (TAG1−/NPY+) portion of the corpus callosum, confirming that it is active in a subpopulation of callosal neurons. These data suggest that exaptation of the AS021 SINE locus might be involved in enhancement of Satb2 expression, leading to the establishment of interhemispheric communication via the corpus callosum, a eutherian-specific brain structure