TRAF6 is a signal transducer that activates IkappaB kinase (IKK) and Jun amino-terminal kinase (JNK) in response to pro-inflammatory mediators such as interleukin-1 (IL-1) and lipopolysaccharides (LPS). IKK activation by TRAF6 requires two intermediary factors, TRAF6-regulated IKK activator 1 (TRIKA1) and TRIKA2 (ref. 5). TRIKA1 is a dimeric ubiquitin-conjugating enzyme complex composed of Ubc13 and Uev1A (or the functionally equivalent Mms2). This Ubc complex, together with TRAF6, catalyses the formation of a Lys 63 (K63)-linked polyubiquitin chain that mediates IKK activation through a unique proteasome-independent mechanism. Here we report the purification and identification of TRIKA2, which is composed of TAK1, TAB1 and TAB2, a protein kinase complex previously implicated in IKK activation through an unknown mechanism. We find that the TAK1 kinase complex phosphorylates and activates IKK in a manner that depends on TRAF6 and Ubc13-Uev1A. Moreover, the activity of TAK1 to phosphorylate MKK6, which activates the JNK-p38 kinase pathway, is directly regulated by K63-linked polyubiquitination. We also provide evidence that TRAF6 is conjugated by the K63 polyubiquitin chains. These results indicate that ubiquitination has an important regulatory role in stress response pathways, including those of IKK and JNK.

Within the vertebrate nervous system, the presence of many different lineages of neurons and glia complicates the molecular characterization of single neuronal populations. In order to elucidate molecular mechanisms underlying the specification and development of corticospinal motor neurons (CSMN), we purified CSMN at distinct stages of development in vivo and compared their gene expression to two other pure populations of cortical projection neurons: callosal projection neurons and corticotectal projection neurons. We found genes that are potentially instructive for CSMN development, as well as genes that are excluded from CSMN and are restricted to other populations of neurons, even within the same cortical layer. Loss-of-function experiments in null mutant mice for Ctip2 (also known as Bcl11b), one of the newly characterized genes, demonstrate that it plays a critical role in the development of CSMN axonal projections to the spinal cord in vivo, confirming that we identified central genetic determinants of the CSMN population.

Toll-like receptors (TLRs) are involved in the recognition of microbial pathogens. A subset of TLRs, TLR7, TLR8 and TLR9, induces antiviral responses by producing interferon-alpha (IFN-alpha). Production of IFN-alpha is dependent on the Toll-interleukin-1 receptor domain-containing adaptor MyD88. Here we show that MyD88 formed a complex with the transcription factor IRF7 but not with IRF3. The death domain of MyD88 interacted with an inhibitory domain of IRF7, and this interaction resulted in activation of the IFN-alpha-dependent promoters. Furthermore, the adaptor molecule TRAF6 also bound and activated IRF7. Ubiquitin ligase activity of TRAF6 was required for IRF7 activation. These results indicate that TLR-mediated IFN-alpha induction requires the formation of a complex consisting of MyD88, TRAF6 and IRF7 as well as TRAF6-dependent ubiquitination.

We study the intrinsic spin Hall conductivity (SHC) in various 5d-transition metals (Ta, W, Re, Os, Ir, Pt, and Au) and 4d-transition metals (Nb, Mo, Tc, Ru, Rh, Pd, and Ag) based on the Naval Research Laboratory tight-binding model, which enables us to perform quantitatively reliable analysis. In each metal, the obtained intrinsic SHC is independent of resistivity in the low resistive regime (ρ < 50µΩcm) whereas it decreases in proportion to ρ −2 in the high resistive regime. In the low resistive regime, the SHC takes a large positive value in Pt and Pd, both of which have approximately nine d-electrons per ion (n d = 9). On the other hand, the SHC takes a large negative value in Ta, Nb, W, and Mo where n d < 5. In transition metals, a conduction electron acquires the trajectory-dependent phase factor that originates from the atomic wavefunction. This phase factor, which is reminiscent of the Aharonov-Bohm phase, is the origin of the SHC in paramagnetic metals and that of the anomalous Hall conductivity in ferromagnetic metals. Furthermore, each transition metal shows huge and positive d-orbital Hall conductivity (OHC), independently of the strength of the spin-orbit interaction (SOI). Since the OHC is much larger than the SHC, it will be possible to realize a orbitronics device made of transition metals.