Retroposons, such as short interspersed elements (SINEs) and long interspersed elements (LINEs), are the major constituents of higher vertebrate genomes. Although there are many examples of retroposons' acquiring function, none has been implicated in the morphological innovations specific to a certain taxonomic group. We previously characterized a SINE family, AmnSINE1, members of which constitute a part of conserved noncoding elements (CNEs) in mammalian genomes. We proposed that this family acquired genomic functionality or was exapted after retropositioning in a mammalian ancestor. Here we identified 53 new AmnSINE1 loci and refined 124 total loci, two of which were further analyzed. Using a mouse enhancer assay, we demonstrate that one SINE locus, AS071, 178 kbp from the gene FGF8 (fibroblast growth factor 8), is an enhancer that recapitulates FGF8 expression in two regions of the developing forebrain, namely the diencephalon and the hypothalamus. Our gain-of-function analysis revealed that FGF8 expression in the diencephalon controls patterning of thalamic nuclei, which act as a relay center of the neocortex, suggesting a role for FGF8 in mammalianspecific forebrain patterning. Furthermore, we demonstrated that the locus, AS021, 392 kbp from the gene SATB2, controls gene expression in the lateral telencephalon, which is thought to be a signaling center during development. These results suggest important roles for SINEs in the development of the mammalian neuronal network, a part of which was initiated with the exaptation of AmnSINE1 in a common mammalian ancestor.conserved noncoding element ͉ enhancer ͉ evolution ͉ mouse

We investigated the driven dynamics of vortices confined to mesoscopic flow channels by means of a dc-rf interference technique. The observed mode-locking steps in the IV curves provide detailed information on how both the number of vortex rows and the lattice structure in each flow channel change with magnetic field. Minima in flow stress occur when an integer number of rows is moving coherently, while maxima appear when the incoherent motion of mixed n and n+/-1 row configurations is predominant. Simulations show that the enhanced pinning at mismatch originates from quasistatic fault zones with misoriented edge dislocations induced by disorder in the channel edges.

Direct observation of vortices by the scanning SQUID microscopy was made on large mesoscopic disks of an amorphous MoGe thin film. Owing to the weak pinning nature of the amorphous film, vortices are able to form geometry induced, (quasi-)symmetric configurations of polygons and concentric shells in the large disks. Systematic measurements made on selected disks allow us to trace not only how the vortex pattern evolves with magnetic field, but also how the vortex polygons change in size and rotate with respect to the disk center. The results are in good agreement with theoretical considerations for mesoscopic disks with sufficiently large diameter. A series of vortex images obtained in a disk with a pinning site reveals a unique line symmetry in vortex configurations, resulting in modifications of the shell filling rule and the magic number.

We measure voltage noise spectra S V ͑f͒ generated by current-driven vortices at various fields B including the peak-effect regime for amorphous Mo x Ge 1−x films with Corbino-disk and striplike contact geometries. Field dependences of the critical current I c and S V ͑f͒ are nearly independent of contact geometries, indicating that edge effects are not important on static or dynamic vortex properties. This is in contrast to the result reported for NbSe 2 crystals with much larger thickness. S V ͑f͒ at low frequency f exhibits a sharp peak just below the peak field B p of I c , where the characteristic time of vortex motion increases significantly. The results suggest the existence of the order-disorder transition and vortex instabilities due to coexisting vortex phases at around B p .

We present a mode locking (ML) phenomenon of vortex matter observed around the peak effect regime of 2H-NbSe2 pure single crystals. The ML features allow us not only to trace how the shear rigidity of driven vortices persists on approaching the second critical field, but also to demonstrate a dynamic melting transition of driven vortices at a given velocity. We observe the velocity dependent melting signatures in the peak effect regime, which reveal a crossover between the disorder-induced transition at small velocity and the thermally induced transition at large velocity. This uncovers the relationship between the peak effect and the thermal melting.PACS numbers: 74.25. Qt, 74.25.Sv Discontinuous jumps in equilibrium magnetization observed well below the mean field line in clean high T c cuprate superconductors [1], have been widely recognized as a hallmark of the thermodynamic melting transition (MT), which separates a vortex solid state, where elastic interaction dominates and quasi-long ranged, crystalline correlations develop in vortex structure, from a vortex liquid state in which thermal fluctuations disrupt the crystalline order and the shear rigidity vanishes.The melting signature is often accompanied by the pronounced peak anomaly of the magnetization or critical current [2], known as the peak effect (PE), originating from the rapid softening of the vortex lattice and the random pinning potential due to disorder quenched in a host material. The close proximity of the MT on the PE has led to a reexamination of the physical properties close to the second critical field H c2 , especially on low T c materials like Nb [3][4][5] and NbSe 2 [6,7]. Various experimental results evidence the pinning-induced structural transformation into a disordered array of vortices, indicating the dominant influence of the quenched disorder in the PE regime [3,[7][8][9]. However, the presence of the MT and its relation with the PE remain controversial [4,5].The effect of the quenched disorder changes remarkably when vortices are driven by a transport current. As proposed theoretically [10][11][12] and experimentally [6,13,14], at low drive the "shaking action" of the random pinning due to the quenched disorder disrupts largely the internal periodicity in moving structure of driven vortices, while at high drive the influence of the disorder diminishes and the elastic interaction becomes dominant, resulting in moving solid states at large velocity.This leads to an unique opportunity to study whether the "driven lattice" undergoes thermally induced MT and also whether the transition occurs in the disorder dominant, PE regime. In this letter, we present experimental evidences for the dynamic melting transition(DMT) of driven lattice observed just above the PE of NbSe 2 by means of mode locking (ML) experiment. ML is a dynamic synchronization between rf drive superimposed on dc drive and collective lattice (elastic) modes excited over driven vortices at internal frequencies f int = qv/a with the average velocity v, the lattice ...

The flow properties of confined vortex matter driven through disordered mesoscopic channels are investigated by mode locking (ML) experiments. The observed ML effects allow to trace the evolution of both the structure and the number of confined rows and their match to the channel width as function of magnetic field. From a detailed analysis of the ML behavior for the case of 3-rows we obtain (i) the pinning frequency fp, (ii) the onset frequency fc for ML (∝ ordering velocity) and (iii) the fraction LML/L of coherently moving 3-row regions in the channel. The field dependence of these quantities shows that, at matching, where LML is maximum, the pinning strength is small and the ordering velocity is low, while at mismatch, where LML is small, both the pinning force and the ordering velocity are enhanced. Further, we find that fc ∝ f 2 p , consistent with the dynamic ordering theory of Koshelev and Vinokur. The microscopic nature of the flow and the ordering phenomena will also be discussed.

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Vertebrate hearts have evolved from undivided tubular hearts of chordate ancestors. One of the most intriguing issues in heart evolution is the abrupt appearance of multichambered hearts in the agnathan vertebrates. To explore the developmental mechanisms behind the drastic morphological changes that led to complex vertebrate hearts, we examined the developmental patterning of the agnathan lamprey Lethenteron japonicum. We isolated lamprey orthologs of genes thought to be essential for heart development in chicken and mouse embryos, including genes responsible for differentiation and proliferation of the myocardium (LjTbx20, LjTbx4/5, and LjIsl1/2A), establishment of left-right heart asymmetry (LjPitxA), and partitioning of the heart tube (LjTbx2/3A), and studied their expression patterns during lamprey cardiogenesis. We confirmed the presence of the cardiac progenitors expressing LjIsl1/2A in the pharyngeal and splanchnic mesoderm and the heart tube of the lamprey. The presence of LjIsl1/2A-positive cardiac progenitor cells in cardiogenesis may have permitted an increase of myocardial size in vertebrates. We also observed LjPitxA expression in the left side of lamprey cardiac mesoderm, suggesting that asymmetric expression of Pitx in the heart has been acquired in the vertebrate lineage. Additionally, we observed LjTbx2/3A expression in the nonchambered myocardium, supporting the view that acquisition of Tbx2/3 expression may have allowed primitive tubular hearts to partition, giving rise to multichambered hearts.