Tcf7l2 is required for left-right asymmetric differentiation of habenular neurons.

BACKGROUND: Although left-right asymmetries are common features of nervous systems, their developmental bases are largely unknown. In the zebrafish epithalamus, dorsal habenular neurons adopt medial (dHbm) and lateral (dHbl) subnuclear character at very different frequencies on the left and right sides. The left-sided parapineal promotes the elaboration of dHbl character in the left habenula, albeit by an unknown mechanism. Likewise, the genetic pathways acting within habenular neurons to control their asymmetric differentiated character are unknown. RESULTS: In a forward genetic screen for mutations that result in loss of habenular asymmetry, we identified two mutant alleles of tcf7l2, a gene that encodes a transcriptional regulator of Wnt signaling. In tcf7l2 mutants, most neurons on both sides differentiate with dHbl identity. Consequently, the habenulae develop symmetrically, with both sides adopting a pronounced leftward character. Tcf7l2 acts cell automously in nascent equipotential neurons, and on the right side, it promotes dHbm and suppresses dHbl differentiation. On the left, the parapineal prevents this Tcf7l2-dependent process, thereby promoting dHbl differentiation. CONCLUSIONS: Tcf7l2 is essential for lateralized fate selection by habenular neurons that can differentiate along two alternative pathways, thereby leading to major neural circuit asymmetries

The natural history of the WRKY–GCM1 zinc fingers and the relationship between transcription factors and transposons

WRKY and GCM1 are metal chelating DNA-binding domains (DBD) which share a four stranded fold. Using sensitive sequence searches, we show that this WRKY–GCM1 fold is also shared by the FLYWCH Zn-finger domain and the DBDs of two classes of Mutator-like element (MULE) transposases. We present evidence that they share a stabilizing core, which suggests a possible origin from a BED finger-like intermediate that was in turn ultimately derived from a C2H2 Zn-finger domain. Through a systematic study of the phyletic pattern, we show that this WRKY–GCM1 superfamily is a widespread eukaryote-specific group of transcription factors (TFs). We identified several new members across diverse eukaryotic lineages, including potential TFs in animals, fungi and Entamoeba. By integrating sequence, structure, gene expression and transcriptional network data, we present evidence that at least two major global regulators belonging to this superfamily in Saccharomyces cerevisiae (Rcs1p and Aft2p) have evolved from transposons, and attained the status of transcription regulatory hubs in recent course of ascomycete yeast evolution. In plants, we show that the lineage-specific expansion of WRKY–GCM1 domain proteins acquired functional diversity mainly through expression divergence rather than by protein sequence divergence. We also use the WRKY–GCM1 superfamily as an example to illustrate the importance of transposons in the emergence of new TFs in different lineages

An Fgf8-Dependent Bistable Cell Migratory Event Establishes CNS Asymmetry

Neuroanatomical and functional asymmetries are universal features of the vertebrate CNS, but how asymmetry is generated is unknown. Here we show that zebrafish fgf8 mutants do not elaborate forebrain asymmetries, demonstrated by the failure of the parapineal nucleus to migrate from its initial midline position to the left side of the brain. Local provision of Fgf8 restores the asymmetric migration of parapineal cells, usually to the left, irrespective of the location of the Fgf8 source. This laterality bias is due to left-sided Nodal signaling and when the bias in Nodal signaling is removed, parapineal cells migrate toward the source of Fgf8 protein. This study presents a mechanism for breaking neuroanatomical symmetry through Fgf8-dependent regulation of bistable left- or right-sided migration of the parapineal. The combined action of Fgf and Nodal signals ensures the establishment of neuroanatomical asymmetries with consistent laterality

Spin waves modes in cobalt nanowires arrays

Cobalt nanowires (NWs) of 40-50 nm average diameter and several micrometers in length were elaborated by electrodeposition process in alumina templates. X-ray diffraction measurements show that all the NWs present a heterogeneous crystalline structure with hcp phase that can be tuned by an appropriate choice of the electrolyte pH. A complex evolution of the magnetic coercivity and squareness with pH is observed in connection with that of the hcp c-axis of the crystalline structure. The spin waves (SWs) propagating into the NWs were investigated by means of the Brillouin light scattering technique. A detailed analysis of the SW spectra allows the identification of dipolar and exchange nature modes propagating within the NWs. Their frequency behavior is successfully described by means of analytical models

Magnetic properties of Mn-implanted 6H-SiC single crystal

The electronic and magnetic structures of Mn-doped 6H-SiC have been investigated using ab initio calculations. Various configurations of Mn sites and vacancy types have been considered. The calculations showed that a substitutional Mn atom at either Si or C sites possesses a magnetic moment. The Mn atom at Si site possesses larger magnetic moment than Mn atom at C site. The magnetic properties of ferromagnetically and antiferromagnetically coupled pair of Mn atoms in the presence of vacancies have also been explored. Our calculations show that antiferromagnetically coupled pair of Mn atoms at Si sites with neighboring C vacancy is magnetically more stable. Relaxation effects were also studied. The results are correlated to the measured magnetic properties obtained for Mn-implanted 6H-SiC for various Mn concentrations. (C) 2012 American Institute of Physics

Experimental study of spin-wave dispersion in Py/Pt film structures in the presence of an interface Dzyaloshinskii-Moriya interaction

Équipe 101 : Nanomagnétisme et électronique de spinInternational audienceBrillouin light scattering (BLS), complemented by ferromagnetic resonance (FMR) characterization, has been used for studying spin-wave (SW) propagation in Py(L)/Pt(6-nm) bilayers of various Py thicknesses (4 nm <= L <= 10 nm). The FMR measurements allowed determination of the pertinent magnetic parameters and revealed the existence of a normal surface anisotropy. A pronounced asymmetry of Damon-Eshbach (DE) wave frequencies has been evidenced by BLS. Therefore, the difference between Stokes and anti-Stokes DE frequencies has been measured versusSWwave number for all the samples. A detailed discussion about the origin of this frequency difference is reported, which concludes that this is due to interface Dzyaloshinskii-Moriya interaction (IDMI)