Observation of the magnon Hall effect

The Hall effect usually occurs in conductors when the Lorentz force acts on a charge current in the presence of a perpendicular magnetic field. Neutral quasi-particles such as phonons and spins can, however, carry heat current and potentially exhibit the thermal Hall effect without resorting to the Lorentz force. We report experimental evidence for the anomalous thermal Hall effect caused by spin excitations (magnons) in an insulating ferromagnet with a pyrochlore lattice structure. Our theoretical analysis indicates that the propagation of the spin waves is influenced by the Dzyaloshinskii-Moriya spin-orbit interaction, which plays the role of the vector potential, much as in the intrinsic anomalous Hall effect in metallic ferromagnets.

Enhanced intrinsic photovoltaic effect in tungsten disulfide nanotubes

The photovoltaic effect in traditional p-n junctions-where a p-type material (with an excess of holes) abuts an n-type material (with an excess of electrons)-involves the light-induced creation of electron-hole pairs and their subsequent separation, generating a current. This photovoltaic effect is particularly important for environmentally benign energy harvesting, and its efficiency has been increased dramatically, almost reaching the theoretical limit¹. Further progress is anticipated by making use of the bulk photovoltaic effect (BPVE)², which does not require a junction and occurs only in crystals with broken inversion symmetry³. However, the practical implementation of the BPVE is hampered by its low efficiency in existing materials^4-10. Semiconductors with reduced dimensionality² or a smaller bandgap^4,5 have been suggested to be more efficient. Transition-metal dichalcogenides (TMDs) are exemplary small-bandgap, two-dimensional semiconductors^11,12 in which various effects have been observed by breaking the inversion symmetry inherent in their bulk crystals^13-15, but the BPVE has not been investigated. Here we report the discovery of the BPVE in devices based on tungsten disulfide, a member of the TMD family. We find that systematically reducing the crystal symmetry beyond mere broken inversion symmetry-moving from a two-dimensional monolayer to a nanotube with polar properties-greatly enhances the BPVE. The photocurrent density thus generated is orders of magnitude larger than that of other BPVE materials. Our findings highlight not only the potential of TMD-based nanomaterials, but also more generally the importance of crystal symmetry reduction in enhancing the efficiency of converting solar to electric power.

Superconductivity in a chiral nanotube

Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity—unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures.

Chirality affects many properties of materials, but how it affects superconductivity remains unclear. Here, Qin et al. report nonreciprocal supercurrent flows in individual nanotubes of WS₂ via ionic gating, evidencing chiral superconducting transport.

A spliceosomal intron binding protein, IBP160, links position-dependent assembly of intron-encoded box C/D snoRNP to pre-mRNA splicing

Pre-mRNA splicing in vertebrates is molecularly linked to other processes. We previously reported that splicing is required for efficient assembly of intron-encoded box C/D small nucleolar ribonucleoprotein (snoRNP). In the spliceosomal C1 complex, snoRNP proteins efficiently assemble onto snoRNA sequences if they are located about 50 nt upstream of the intron branchpoint. Here, we identify the splicing factor responsible for coupling snoRNP assembly to intron excision. Intron binding protein (IBP) 160, a helicase-like protein previously detected in the spliceosomal C1 complex, binds the pre-mRNA in a sequence-independent manner, contacting nucleotides 33-40 upstream of the intron branch site, regardless of whether a snoRNA is present. Depletion of IBP160 abrogates snoRNP assembly in vitro. IBP160 binding directly to a snoRNA located too close to the intron branch site interferes with snoRNP assembly. Thus, IBP160 is the key factor linking snoRNP biogenesis and perhaps other postsplicing events to pre-mRNA splicing.

Efficient oligonucleotide-mediated degradation of nuclear noncoding RNAs in mammalian cultured cells

Recent large-scale transcriptome analyses have revealed that large numbers of noncoding RNAs (ncRNAs) are transcribed from mammalian genomes. They include small nuclear RNAs (snRNAs), small nucleolar RNAs (snoRNAs), and longer ncRNAs, many of which are localized to the nucleus, but which have remained functionally elusive. Since ncRNAs are only known to exist in mammalian species, established experimental systems, including the Xenopus oocyte system and yeast genetics, are not available for functional analysis. RNA interference (RNAi), commonly used for analysis of protein-coding genes, is effective in eliminating cytoplasmic mRNAs, but not nuclear RNAs. To circumvent this problem, we have refined the system for knockdown of nuclear ncRNAs with chemically modified chimeric antisense oligonucleotides (ASO) that were efficiently introduced into the nucleus by nucleofection. Under optimized conditions, our system appeared to degrade at least 20 different nuclear ncRNA species in multiple mammalian cell lines with high efficiency and specificity. We also confirmed that our method had greatly improved knockdown efficiency compared with that of the previously reported method in which ASOs are introduced with transfection reagents. Furthermore, we have confirmed the expected phenotypic alterations following knockdown of HBII295 snoRNA and U7 snRNA, which resulted in a loss of site-specific methylation of the artificial RNA and the appearance of abnormal polyadenylated histone mRNA species with a concomitant delay of the cell cycle S phase, respectively. In summary, we believe that our system is a powerful tool to explore the biological functions of the large number of nuclear ncRNAs with unknown function.

Involvement of satellite I noncoding RNA in regulation of chromosome segregation

Human centromeres consist of repetitive sequences from which satellite I noncoding RNAs are transcribed. We found that knockdown of satellite I RNA causes abnormal chromosome segregation and generation of nuclei with a grape-shape phenotype. Co-immunoprecipitation experiments showed that satellite I RNA associates with Aurora B, a component of the chromosome passenger complex (CPC) regulating proper attachment of microtubules to kinetochores, in mitotic HeLa cells. Satellite I RNA was also shown to associate with INCENP, another component of the CPC. In addition, depletion of satellite I RNA resulted in up-regulation of kinase activity of Aurora B and delocalization of the CPC from the centromere region. These results suggest that satellite I RNA is involved in chromosome segregation through controlling activity and centromeric localization of Aurora B kinase.

Introns play an essential role in splicing-dependent formation of the exon junction complex

Pre-mRNA splicing specifically deposits the exon junction complex (EJC) onto spliced mRNA, which is important for downstream events. Here, we show that EJC components are primarily recruited to the spliceosome by association with the intron via the intron-binding protein, IBP160. This initial association of EJC components occurs in the absence of the final EJC-binding site on the exon. RNA interference (RNAi) knockdown of IBP160 arrested EJC association with cytoplasmic RNAs following nonsense-mediated decay. We propose that the intron has a crucial role in the early steps of EJC formation and is indispensable for the subsequent formation of a functional EJC.

The nucleolus is involved in mRNA export from the nucleus in fission yeast

To elucidate the mechanism of mRNA export from the nucleus, we isolated five novel temperature-sensitive mutants (ptr7 to ptr11) that accumulate poly(A)(+) RNA in the nuclei at the nonpermissive temperature in Schizosaccharomyces pombe. Of those, the ptr11 mutation was found in the top2(+) gene encoding DNA topoisomerase II. In addition to the nuclear accumulation of poly(A)(+) RNA, ptr11 exhibited the cut (cell untimely torn) phenotype at the nonpermissive temperature, like the previously isolated mutant, ptr4. In these two mutants, cytokinesis occurred without prior nuclear division, resulting in cleavage of the undivided nuclei by the septum. To investigate the relationship between mRNA export defects and the cut phenotype observed in ptr4 and ptr11, we analyzed 11 other mutants displaying the cut phenotype and found that all these tested mutants accumulate poly(A)(+) mRNA in the aberrantly cleaved nuclei. Interestingly, nuclear accumulation of poly(A)(+) mRNA was observed only in the anucleolate nuclei produced by aberrant cytokinesis. In addition, nuc1, the S. pombe mutant exhibiting a collapsed nucleolus, trapped poly(A)(+) mRNA in the nucleolar region at the nonpermissive temperature. In ptr11 and nuc1, mRNA transcribed from the intron-containing TBP gene showed nuclear accumulation, but not transcripts from the intron-less TBP cDNA, suggesting that the export pathway differs between the spliced and unspliced TBP mRNAs. These findings support the notion that a subset of mRNAs in yeast is exported from the nucleus through transient association with the nucleolus.

Tissue-specific splicing regulator Fox-1 induces exon skipping by interfering E complex formation on the downstream intron of human F1gamma gene

Fox-1 is a regulator of tissue-specific splicing, via binding to the element (U)GCAUG in mRNA precursors, in muscles and neuronal cells. Fox-1 can regulate splicing positively or negatively, most likely depending on where it binds relative to the regulated exon. In cases where the (U)GCAUG element lies in an intron upstream of the alternative exon, Fox-1 protein functions as a splicing repressor to induce exon skipping. Here we report the mechanism of exon skipping regulated by Fox-1, using the hF1γ gene as a model system. We found that Fox-1 induces exon 9 skipping by repressing splicing of the downstream intron 9 via binding to the GCAUG repressor elements located in the upstream intron 8. In vitro splicing analyses showed that Fox-1 prevents formation of the pre-spliceosomal early (E) complex on intron 9. In addition, we located a region of the Fox-1 protein that is required for inducing exon skipping. Taken together, our data show a novel mechanism of how RNA-binding proteins regulate alternative splicing.

Giant thermal Hall effect in multiferroics

Multiferroics, in which dielectric and magnetic orders coexist and couple with each other, attract renewed interest for their cross-correlated phenomena, offering a fundamental platform for novel functionalities. Elementary excitations in such systems are strongly affected by the lattice-spin interaction, as exemplified by the electromagnons and the magneto-thermal transport. Here we report an unprecedented coupling between magnetism and phonons in multiferroics, namely, the giant thermal Hall effect. The thermal transport of insulating polar magnets (Zn_xFe_1-x)₂Mo₃O₈ is dominated by phonons, yet extremely sensitive to the magnetic structure. In particular, large thermal Hall conductivities are observed in the ferrimagnetic phase, indicating unconventional lattice-spin interactions and a new mechanism for the Hall effect in insulators. Our results show that the thermal Hall effect in multiferroic materials can be an effective probe for strong lattice-spin interactions and provide a new tool for magnetic control of thermal currents.

Radial Spin Texture in Elemental Tellurium with Chiral Crystal Structure

The chiral crystal is characterized by a lack of mirror symmetry and inversion center, resulting in the inequivalent right- and left-handed structures. In the noncentrosymmetric crystal structure, the spin and momentum of electrons are expected to be locked in the reciprocal space with the help of the spin-orbit interaction. To reveal the spin textures of chiral crystals, we investigate the spin and electronic structure in a p-type semiconductor, elemental tellurium, with the simplest chiral structure by using spin- and angle-resolved photoemission spectroscopy. Our data demonstrate that the highest valence band crossing the Fermi level has a spin component parallel to the electron momentum around the Brillouin zone corners. Significantly, we have also confirmed that the spin polarization is reversed in the crystal with the opposite chirality. The results indicate that the spin textures of the right- and left-handed chiral crystals are hedgehoglike, leading to unconventional magnetoelectric effects and nonreciprocal phenomena.

Identification and characterization of human non-coding RNAs with tissue-specific expression

We have examined the expression profile of selected non-coding RNAs (ncRNAs) in 11 human tissues. Among 5489 full-length cDNA clones annotated as non-protein-coding transcripts in the H-Invitational database, we chose 150 clones for further analysis based on their gene structure and EST information. Expression profiling using quantitative RT-PCR and Northern blot hybridization revealed that the majority of the selected ncRNAs exhibited tissue specificity: 67% are predominantly expressed in a restricted subset of tissues. The absolute quantification of representative ncRNAs revealed that the majority of ncRNAs are expressed as low abundance transcripts. A comparative genomic analysis revealed that only 27% of the selected ncRNAs have mouse counterparts. Since the expression patterns of the human ncRNAs having no mouse counterparts remain to be similar to those of the mouse ncRNAs, the expression patterns of the selected ncRNAs may be conserved between human and mouse.

The chloroplast infA gene with a functional UUG initiation codon

All chloroplast genes reported so far possess ATG start codons and sometimes GTGs as an exception. Sequence alignments suggested that the chloroplast infA gene encoding initiation factor 1 in the green alga Chlorella vulgaris has TTG as a putative initiation codon. This gene was shown to be transcribed by RT-PCR analysis. The infA mRNA was translated accurately from the UUG codon in a tobacco chloroplast in vitro translation system. Mutation of the UUG codon to AUG increased translation efficiency approximately 300-fold. These results indicate that the UUG is functional for accurate translation initiation of Chlorella infA mRNA but it is an inefficient initiation codon.

DDX41 coordinates RNA splicing and transcriptional elongation to prevent DNA replication stress in hematopoietic cells

Myeloid malignancies with DDX41 mutations are often associated with bone marrow failure and cytopenia before overt disease manifestation. However, the mechanisms underlying these specific conditions remain elusive. Here, we demonstrate that loss of DDX41 function impairs efficient RNA splicing, resulting in DNA replication stress with excess R-loop formation. Mechanistically, DDX41 binds to the 5' splice site (5'SS) of coding RNA and coordinates RNA splicing and transcriptional elongation; loss of DDX41 prevents splicing-coupled transient pausing of RNA polymerase II at 5'SS, causing aberrant R-loop formation and transcription-replication collisions. Although the degree of DNA replication stress acquired in S phase is small, cells undergo mitosis with under-replicated DNA being remained, resulting in micronuclei formation and significant DNA damage, thus leading to impaired cell proliferation and genomic instability. These processes may be responsible for disease phenotypes associated with DDX41 mutations.

Thermal Generation of Spin Current in an Antiferromagnet

The longitudinal spin Seebeck effect has been investigated for a uniaxial antiferromagnetic insulator Cr(2)O(3), characterized by a spin-flop transition under magnetic field along the c axis. We have found that a temperature gradient applied normal to the Cr(2)O(3)/Pt interface induces inverse spin Hall voltage of spin-current origin in Pt, whose magnitude turns out to be always proportional to magnetization in Cr(2)O(3). The possible contribution of the anomalous Nernst effect is confirmed to be negligibly small. The above results establish that an antiferromagnetic spin wave can be an effective carrier of spin current.

RBMX is a component of the centromere noncoding RNP complex involved in cohesion regulation

Satellite I RNA, a noncoding (nc)RNA transcribed from repetitive regions in human centromeres, binds to Aurora kinase B and forms a ncRNP complex required for chromosome segregation. To examine its function in this process, we purified satellite I ncRNP complex from nuclear extracts prepared from asynchronized or mitotic (M) phase-arrested HeLa cells and then carried out LC/MS to identify proteins bound to satellite I RNA. RBMX (RNA-binding motif protein, X-linked), which was isolated from M phase-arrested cells, was selected for further characterization. We found that RBMX associates with satellite I RNA only during M phase. Knockdown of RBMX induced premature separation of sister chromatid cohesion and abnormal nuclear division. Likewise, knockdown of satellite I RNA also caused premature separation of sister chromatids during M phase. The amounts of RBMX and Sororin, a cohesion regulator, were reduced in satellite I RNA-depleted cells. These results suggest that satellite I RNA plays a role in stabilizing RBMX and Sororin in the ncRNP complex to maintain proper sister chromatid cohesion.

The intron in centromeric noncoding RNA facilitates RNAi-mediated formation of heterochromatin

In fission yeast, the formation of centromeric heterochromatin is induced through the RNA interference (RNAi)-mediated pathway. Some pre-mRNA splicing mutants (prp) exhibit defective formation of centromeric heterochromatin, suggesting that splicing factors play roles in the formation of heterochromatin, or alternatively that the defect is caused by impaired splicing of pre-mRNAs encoding RNAi factors. Herein, we demonstrate that the splicing factor spPrp16p is enriched at the centromere, and associates with Cid12p (a factor in the RNAi pathway) and the intron-containing dg ncRNA. Interestingly, removal of the dg intron, mutations of its splice sites, or replacement of the dg intron with an euchromatic intron significantly decreased H3K9 dimethylation. We also revealed that splicing of dg ncRNA is repressed in cells and its repression depends on the distance from the transcription start site to the intron. Inefficient splicing was also observed in other intron-containing centromeric ncRNAs, dh and antisense dg, and splicing of antisense dg ncRNA was repressed in the presence of the RNAi factors. Our results suggest that the introns retained in centromeric ncRNAs work as facilitators, co-operating with splicing factors assembled on the intron and serving as a platform for the recruitment of RNAi factors, in the formation of centromeric heterochromatin.

Formation of centromeric heterochromatin is required for correct segregation of sister chromatids during mitosis. In fission yeast, formation of heterochromatin at centromeres is performed through the RNA interference (RNAi) system, which involves processing of noncoding RNAs transcribed from the centromeres. We found that the intron in the centromeric dg ncRNAs facilitates formation of centromeric heterochromatin in fission yeast. We showed that the splicing factor spPrp16p associates with the RNAi factor and intron-containing dg ncRNA. Removal of or mutations in the dg intron significantly decreased H3K9 dimethylation, suggesting that the intron and associated splicing factors serve as a platform for recruitment of RNAi factors. Inefficient splicing is a hallmark of intron-containing centromeric ncRNAs. Such repression of splicing seems to be important for facilitation of heterochromatin formation. Introns in euchromatic regions are removed by splicing to generate functional RNAs, whereas centromeric introns are retained in ncRNAs by splicing repression and play roles in gene silencing. Our findings shed light on the novel roles of introns in epigenetic regulation of gene expression and heterochromatin formation.

A mutation in the gene involved in sister chromatid separation causes a defect in nuclear mRNA export in fission yeast

Fission yeast ptr4-1 is one of the mRNA transport mutants that accumulate poly(A)(+) RNA in the nuclei at the nonpermissive temperature. We cloned the ptr4(+) gene and found that it is identical with the cut1(+) gene essential for chromosome segregation during mitosis. ptr4/cut1 has no defects in nucleocytoplasmic transport of a protein, indicative of a specific blockage of mRNA export by this mutation. A mutant of Cut2p cooperating with Cut1p in sister chromatid separation also showed defective mRNA export at the nonpermissive temperature. Our results suggest a novel linkage between the cell division cycle and nuclear mRNA export in eukaryotic cells.

DEAH box RNA helicase DHX38 associates with satellite I noncoding RNA involved in chromosome segregation

Noncoding (nc) RNA called satellite I is transcribed from the human centromere region. Depletion of this ncRNA results in abnormal nuclear morphology because of defects in chromosome segregation. Some protein factors interact with this ncRNA and function as a component of a nc ribonucleoprotein (RNP) complex in mitotic regulation. Here, we found that DHX38, a pre-mRNA splicing-related DEAH box RNA helicase, interacts with satellite I ncRNA. Depletion of DHX38 resulted in defective chromosome segregation similar to knockdown of satellite I ncRNA. Interaction between DHX38 and ncRNA was interphase-specific, but DHX38 depletion affected the function of Aurora B, which associated with satellite I ncRNA at mitotic phase. Based on these findings, we suggest that DHX38 has a role in mitotic regulation as a component of the satellite I ncRNP complex at interphase.

Discovery, characterization and functional improvement of kumamonamide as a novel plant growth inhibitor that disturbs plant microtubules

The discovery and useful application of natural products can help improve human life. Chemicals that inhibit plant growth are broadly utilized as herbicides to control weeds. As various types of herbicides are required, the identification of compounds with novel modes of action is desirable. In the present study, we discovered a novel N-alkoxypyrrole compound, kumamonamide from Streptomyces werraensis MK493-CF1 and established a total synthesis procedure. Resulted in the bioactivity assays, we found that kumamonamic acid, a synthetic intermediate of kumamonamide, is a potential plant growth inhibitor. Further, we developed various derivatives of kumamonamic acid, including a kumamonamic acid nonyloxy derivative (KAND), which displayed high herbicidal activity without adverse effects on HeLa cell growth. We also detected that kumamonamic acid derivatives disturb plant microtubules; and additionally, that KAND affected actin filaments and induced cell death. These multifaceted effects differ from those of known microtubule inhibitors, suggesting a novel mode of action of kumamonamic acid, which represents an important lead for the development of new herbicides.