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Collective cell migration is the coordinated movement of multiple cells connected by cadherin-based adherens junctions and is essential for physiological and pathological processes. Cadherins undergo dynamic intracellular trafficking, and their surface level is determined by a balance between endocytosis, recycling and degradation. However, the regulatory mechanism of cadherin turnover in collective cell migration remains elusive. In this study, we show that the Bin/amphiphysin/Rvs (BAR) domain protein pacsin 2 (protein kinase C and casein kinase substrate in neurons protein 2) plays an essential role in collective cell migration by regulating N-cadherin (also known as CDH2) endocytosis in human cancer cells. Pacsin 2-depleted cells formed cell–cell contacts enriched with N-cadherin and migrated in a directed manner. Furthermore, pacsin 2-depleted cells showed attenuated internalization of N-cadherin from the cell surface. Interestingly, GST pull-down assays demonstrated that the pacsin 2 SH3 domain binds to the cytoplasmic region of N-cadherin, and expression of an N-cadherin mutant defective in binding to pacsin 2 phenocopied pacsin 2 RNAi cells both in cell contact formation and N-cadherin endocytosis. These data support new insights into a novel endocytic route of N-cadherin in collective cell migration, highlighting pacsin 2 as a possible therapeutic target for cancer metastasis.

High-speed atomic force microscopy (HS-AFM) is a powerful tool for studying the dynamics of biomolecules in vitro because of its high temporal and spatial resolution. However, multi-functionalization, such as combination with complementary measurement methods, environment control, and large-scale mechanical manipulation of samples, is still a complex endeavor due to the inherent design and the compact sample scanning stage. Emerging tip-scan HS-AFM overcame this design hindrance and opened a door for additional functionalities. In this study, we designed a motor-driven stretching device to manipulate elastic substrates for HS-AFM imaging of biomolecules under controllable mechanical stimulation. To demonstrate the applicability of the substrate stretching device, we observed a microtubule buckling by straining the substrate and actin filaments linked by α-actinin on a curved surface. In addition, a BAR domain protein BIN1 that senses substrate curvature was observed while dynamically controlling the surface curvature. Our results clearly prove that large-scale mechanical manipulation can be coupled with nanometer-scale imaging to observe biophysical effects otherwise obscured.

Cell migration is essential for both physiological and pathological processes such as embryonic morphogenesis, wound repair and metastasis of cancer cells. Collective cell migration is the coordinated movement of multiple cells connected with cadherin-based adherence junctions. Cadherins undergo dynamic intracellular trafficking and their surface level is determined by a balance between endocytosis, recycling and degradation. However, regulatory mechanisms of cadherin turnover in the collective cell migration remain to be elucidated.In this study, we show that a BAR domain protein pacsin 2 plays an essential role in collective cell migration by regulating the internalization of N-cadherin in human bladder cancer cells T24. Pacsin 2 and its associating GTPase dynamin 2 colocalized with N-cadherin at the cell periphery in T24 cells. Depletion of either pacsin 2 or dynamin 2 induced interdigitating cell-cell contacts enriched with N-cadherin. Imaging analyses of the wound healing assay showed that pacsin 2-depleted T24 cells migrated in a collective and directed manner in contrast with randomly migrating control cells. Furthermore, cell-surface biotinylation assay showed that internalization of N-cadherin is attenuated in pacsin 2-depleted cells. Interestingly, the GST-pulldown assay demonstrated that the SH3 domain of pacsin 2 binds to the cytoplasmic domain of N-cadherin, suggesting that surface levels of N-cadherin are regulated by pacsin 2-mediated endocytosis. These data support new insights into a novel endocytic route of N-cadherin in collective cell migration providing pacsin 2 as a possible therapeutic target for cancer metastasis.

Dynamin 1 is a neuronal endocytic protein that participates in vesicle formation by scission of invaginated membranes. Dynamin 1 is also expressed in the kidney; however, its physiological significance to this organ remains unknown. Here, we show that dynamin 1 is crucial for microtubule organization and stabilization in glomerular podocytes. By immunofluorescence and immunoelectron microscopy, dynamin 1 was concentrated at microtubules at primary processes in rat podocytes. By immunofluorescence of differentiated mouse podocytes (MPCs), dynamin 1 was often colocalized with microtubule bundles, which radially arranged toward periphery of expanded podocyte. In dynamin 1-depleted MPCs by RNAi, alpha-tubulin showed a dispersed linear filament-like localization, and microtubule bundles were rarely observed. Furthermore, dynamin 1 depletion resulted in the formation of discontinuous, short acetylated alpha-tubulin fragments, and the decrease of microtubule-rich protrusions. Dynamins 1 and 2 double-knockout podocytes showed dispersed acetylated alpha-tubulin and rare protrusions. In vitro, dynamin 1 polymerized around microtubules and cross-linked them into bundles, and increased their resistance to the disassembly-inducing reagents Ca(2+)and podophyllotoxin. In addition, overexpression and depletion of dynamin 1 in MPCs increased and decreased the nocodazole resistance of microtubules, respectively. These results suggest that dynamin 1 supports the microtubule bundle formation and participates in the stabilization of microtubules.

SUMMARYThe Philippine Sea plate (PHS) is subducting beneath southwest Japan from the Nankai Trough. In this region, deep low-frequency earthquakes/tremors (LFEs) are active and their epicentres are distributed along the downdip of the source region of M8-class earthquakes that have occurred every 100–150 yr. The LFE activity may potentially be strongly related to the occurrence of great earthquakes between tectonic plates. To investigate the structural features around the LFEs, we applied teleseismic receiver function (RF) analysis to the seismograms observed at permanent and temporal seismograph stations in western Shikoku and we detected seismological evidence of a slab dehydration reaction linked to LFE activity. Based on the first-order harmonic decomposition of RFs, we first estimated the average plunge azimuth of the PHS beneath western Shikoku. Considering the backazimuth dependence of converted phase amplitude, we constructed the cross-section of the radial component RFs, excluding the incoming waveform data from the updip directions of the dipping slab. In this profile, the parallel negative and positive P-to-S converted phase alignment within a distance of 10 km were imaged. These phase alignments corresponded to the top of the slab and the slab Moho discontinuity, respectively. At the northern side of the profile, the landward (continental) Moho was also detected. In the region where LFEs were actively distributed, both the landward Moho and slab surface were unclear. The second-order harmonic decomposition of RFs for several kilometres above the slab Moho indicated that the anisotropic symmetry axes suddenly changed at the southern limit of the LFE active region; the fast axes in the region were normal to the trench though axes in the southern area were parallel. According to the thermal and pressure condition, a phase transition with a dehydration reaction can occur in the oceanic crust near the southern edge of the LFE active region. Once the dehydration process advances, released water causes the serpentinization of the mantle material near the slab surface and the corresponding seismic velocity decreases. The impedance contrast decreases at the boundary between the lower crust and the mantle wedge, as well as that between the mantle wedge and oceanic crust; therefore, the amplitudes of the converted phases at these boundaries also become small. Considering that serpentinite ordinarily has strong anisotropy with a seismic fast axis direct to the shear direction, all features observed are evidence of the dehydration process in the flat slab.

Podosomes are actin-rich adhesion structures formed in a variety of cell types, such as monocytic cells or cancer cells, to facilitate attachment to and degradation of the extracellular matrix (ECM). Previous studies showed that dynamin 2, a large GTPase involved in membrane remodeling and actin organization, is required for podosome function. However, precise roles of dynamin 2 at the podosomes remain to be elucidated. In this study, we identified a BAR (Bin-Amphiphysin-Rvs167) domain protein pacsin 2 as a functional partner of dynamin 2 at podosomes. Dynamin 2 and pacsin 2 interact and co-localize to podosomes in Src-transformed NIH 3T3 (NIH-Src) cells. RNAi of either dynamin 2 or pacsin 2 in NIH-Src cells inhibited podosome formation and maturation, suggesting essential and related roles at podosomes. Consistently, RNAi of pacsin 2 prevented dynamin 2 localization to podosomes, and reciprocal RNAi of dynamin 2 prevented pacsin 2 localization to podosomes. Taking these results together, we conclude that dynamin 2 and pacsin 2 co-operatively regulate organization of podosomes in NIH-Src cells.

International audience; We use ambient-noise-based seismic monitoring to detect an anomalous seismic velocity decrease (∼0.01%) widely distributed in Honshu that arose about 1 year after the 2011 Mw 9.0 Tohoku-Oki earthquake. The anomaly is located along the central quaternary volcanic axis, and it suggests that the changes are related to volcanic processes. After correction for possible external environmental forcing-related velocity changes, the anomaly in the seismic velocity remains, which implies that it is associated with some internal physical process. We show a general strong positive correlation between the seismic velocity changes and the intensity of ground motion derived from the daily cumulative seismic moment. However, the lack of correlation during the anomaly itself reveals that this reduction is not directly caused by earthquake shaking. Tiltmeter low-pass observations show temporal variations that are correlated with the velocity changes. These observations strengthen the hypothesis of actual physical deformation. A previously reported decrease in fault strength (∼10%) for the same period as the velocity anomaly further supports a physical property change in the upper crust. We also note a simultaneous increase in activity of low-frequency events in the volcanic area, which suggests an increase in pore pressure in the upper crust. We propose that the observed anomalous seismic velocity decrease in early 2012 is due to an increase in pore pressure induced by an upward fluid migration, which at the same time triggered the increase in fluid-driven swarm seismicity and low-frequency events. We recall the depth-dependent seismic velocity changes in Honshu and derive an average diffusion of 1 m2/s over around 11 months after the Tohoku-Oki earthquake.

Membrane remodeling is required for dynamic cellular processes such as cell division, polarization, and motility. BAR domain proteins and dynamins are key molecules in membrane remodeling that work together for membrane deformation and fission. In striated muscles, sarcolemmal invaginations termed T-tubules are required for excitation–contraction coupling. BIN1 and DNM2, which encode a BAR domain protein BIN1 and dynamin 2, respectively, have been reported to be causative genes of centronuclear myopathy (CNM), a hereditary degenerative disease of skeletal muscle, and deformation of T-tubules is often observed in the CNM patients. However, it remains unclear how BIN1 and dynamin 2 are implicated in T-tubule biogenesis and how mutations in these molecules cause CNM to develop. Here, using an in cellulo reconstitution assay, we demonstrate that dynamin 2 is required for stabilization of membranous structures equivalent to T-tubules. GTPase activity of wild-type dynamin 2 is suppressed through interaction with BIN1, whereas that of the disease-associated mutant dynamin 2 remains active due to lack of the BIN1-mediated regulation, thus causing aberrant membrane remodeling. Finally, we show that in cellulo aberrant membrane remodeling by mutant dynamin 2 variants is correlated with their enhanced membrane fission activities, and the results can explain severity of the symptoms in patients. Thus, this study provides molecular insights into dysregulated membrane remodeling triggering the pathogenesis of DNM2-related CNM.

Noise-based crustal seismic velocity changes are known to be affected by environmental perturbations, such as rainfall, atmospheric pressure loading, and temperature changes. Similar to geodetic observations, these external perturbations can mask the effects of tectonic and volcanic processes. In this study, we benefit from the dense Hi-net short-period seismic network that covers the entire Japan to measure continuous changes in seismic velocities over a few years, using noise-based seismic monitoring. Some strong seasonal seismic velocity changes are observed in both southern Japan (Kyushu Island) and northern Japan (Hokkaido Island). Decreasing of seismic velocities in summer in southern Japan can be clearly explained by a model of increased crustal fluid pore pressure associated with high rainfall. In northern Japan, it is necessary to adopt a more complex model to explain the observed seismic velocity variations, which takes into account precipitation, snow depth, and sea level changes. Moreover, western and eastern Hokkaido Island show very different responses to these different external perturbations. The models developed are used to remove the seasonal components of the seismic velocity changes. The minimum remaining detectable seismic velocity change reduces to 10−5, which allows detection of crustal responses to small earthquakes that are previously hidden in the strong seasonal perturbations.

We have generated a high-resolution catalog called the “Japan Unified hIgh-resolution relocated Catalog for Earthquakes” (JUICE), which can be used to evaluate the geometry and seismogenic depth of active faults in Japan. We relocated > 1.1 million hypocenters from the NIED Hi-net catalog for events which occurred between January 2001 and December 2012, to a depth of 40 km. We apply a relative hypocenter determination method to the data in each grid square, in which entire Japan is divided into 1257 grid squares to parallelize the relocation procedure. We used a double-difference method, incorporating cross-correlating differential times as well as catalog differential times. This allows us to resolve, in detail, a seismicity distribution for the entire Japanese Islands. We estimated location uncertainty by a statistical resampling method, using Jackknife samples, and show that the uncertainty can be within 0.37 km in the horizontal and 0.85 km in the vertical direction with a 90% confidence interval for areas with good station coverage. Our seismogenic depth estimate agrees with the lower limit of the hypocenter distribution for a recent earthquake on the Kamishiro fault (2014, Mj 6.7), which suggests that the new catalog should be useful for estimating the size of future earthquakes for inland active faults.

The endocytic protein dynamin participates in the formation of actin-based membrane protrusions such as podosomes, pseudopodia, and invadopodia, which facilitate cancer cell migration, invasion, and metastasis. However, the role of dynamin in the formation of actin-based membrane protrusions at the leading edge of cancer cells is unclear. In this study, we demonstrate that the ubiquitously expressed dynamin 2 isoform facilitates cell migration by stabilizing F-actin bundles in filopodia of the lung cancer cell line H1299. Pharmacological inhibition of dynamin 2 decreased cell migration and filopodial formation. Furthermore, dynamin 2 and cortactin mostly colocalized along F-actin bundles in filopodia of serum-stimulated H1299 cells by immunofluorescent and immunoelectron microscopy. Knockdown of dynamin 2 or cortactin inhibited the formation of filopodia in serum-stimulated H1299 cells, concomitant with a loss of F-actin bundles. Expression of wild-type cortactin rescued the punctate-like localization of dynamin 2 and filopodial formation. The incubation of dynamin 2 and cortactin with F-actin induced the formation of long and thick actin bundles, with these proteins colocalizing at F-actin bundles. A depolymerization assay revealed that dynamin 2 and cortactin increased the stability of F-actin bundles. These results indicate that dynamin 2 and cortactin participate in cell migration by stabilizing F-actin bundles in filopodia. Taken together, these findings suggest that dynamin might be a possible molecular target for anticancer therapy.

Fifty-five organic substances including volatile organic compounds (VOCs) and aldehydes present in indoor air were measured from 24 car cabins in Japan. A screening-level risk assessment was also performed. Acetaldehyde (3.81–36.0 μg/m3), formaldehyde (3.26–26.7 μg/m3), n-tetradecane (below the method quantification limit (3), toluene (4.23–78.3μg/m3), and n-undecane (3) concentrations exceeded method detection limits in all the investigated car cabins. Ratios between indoor and outdoor concentrations revealed that most organic compounds originated from the car interior materials. Total volatile organic compound (TVOC) concentrations in 14 car cabins (58% of all car cabins) exceeded the advisable values established by the Ministry of Health, Labour and Welfare of Japan (400 μg/m3). The highest TVOC concentration (1136 μg/m3) was found in a new car (only one month since its purchase date). Nevertheless, TVOC concentrations exceeded the advisable value even for cars purchased over 10 years ago. Hazard quotients (HQs) for formaldehyde obtained using measured median and highest concentrations in both exposure scenarios for occupational use (residential time in a car cabin was assumed to be 8 h) were higher than that expected, a threshold indicative of potential adverse effects. Under the same exposure scenarios, HQ values for all other organic compounds remained below this threshold.

Dynamin copolymerizes with cortactin to form a ring‑like complex that bundles and stabilizes actin filaments. Actin bundle formation is crucial for generation of filopodia and lamellipodia, which guide migration, invasion, and metastasis of cancer cells. However, it is unknown how the dynamin‑cortactin complex regulates actin bundle formation. The present study investigated phosphorylation of cortactin by cyclin‑dependent kinase 5 (CDK5) and its effect on actin bundle formation by the dynamin‑cortactin complex. CDK5 directly phosphorylated cortactin at T145/T219 in vitro. Phosphomimetic mutants in which one or both of these threonine residues was substituted by aspartate were used. The three phosphomimetic mutants (T145D, T219D and T145DT219D) had a decreased affinity for F‑actin. Furthermore, electron microscopy demonstrated that these phosphomimetic mutants could not form a ring‑like complex with dynamin 1. Consistently, the dynamin 1‑phosphomimetic cortactin complexes exhibited decreased actin‑bundling activity. Expression of the phosphomimetic mutants resulted in not only aberrant lamellipodia and short filopodia but also cell migration in NG108‑15 glioma‑derived cells. These results indicate that phosphorylation of cortactin by CDK5 regulates formation of lamellipodia and filopodia by modulating dynamin 1/cortactin‑dependent actin bundling. Taken together, these findings suggest that CDK5 is a potential molecular target for anticancer therapy.

Dynamin copolymerizes with cortactin to form a ring-like complex that bundles and stabilizes actin filaments. Actin bundle formation is crucial for generation of filopodia and lamellipodia, which guide migration, invasion, and metastasis of cancer cells. However, it is unknown how the dynamin-cortactin complex regulates actin bundle formation. The present study investigated phosphorylation of cortactin by cyclin-dependent kinase 5 (CDK5) and its effect on actin bundle formation by the dynamin-cortactin complex. CDK5 directly phosphorylated cortactin at T145/T219 in vitro. Phosphomimetic mutants in which one or both of these threonine residues was substituted by aspartate were used. The three phosphomimetic mutants (T145D, T219D and T145DT219D) had a decreased affinity for F-actin. Furthermore, electron microscopy demonstrated that these phosphomimetic mutants could not form a ring-like complex with dynamin 1. Consistently, the dynamin 1-phosphomimetic cortactin complexes exhibited decreased actin-bundling activity. Expression of the phosphomimetic mutants resulted in not only aberrant lamellipodia and short filopodia but also cell migration in NG108-15 glioma-derived cells. These results indicate that phosphorylation of cortactin by CDK5 regulates formation of lamellipodia and filopodia by modulating dynamin 1/cortactin-dependent actin bundling. Taken together, these findings suggest that CDK5 is a potential molecular target for anticancer therapy.

Background Information Cortactin contributes to growth cone morphogenesis by forming with dynamin, ring-shaped complexes that mechanically bundle and stabilise F-actin. However, the regulatory mechanism of cortactin action is poorly understood. Results Immunofluorescence microscopy revealed that protein kinase C (PKC) α colocalises with cortactin at growth cone filopodia in SH-SY5Y neuroblastoma cells. PKC activation by phorbol 12-myristate 13-acetate causes cortactin phosphorylation, filopodial retraction and F-actin-bundle loss. Moreover, PKCα directly phosphorylates cortactin in vitro at S135/T145/S172, mitigating both cortactin's actin-binding and actin-crosslinking activity, whereas cellular expression of a phosphorylation-mimetic cortactin mutant hinders filopodial formation with a significant decrease of actin bundles. Conclusions Our results indicate that PKC-mediated cortactin phosphorylation might be implicated in the maintenance of growth cone.

In models for strain-partitioning at obliquely-convergent plate boundaries, trench-parallel slip occurs on a vertical fault. Trench-parallel slip at the Nankai subduction zone, SW Japan, is mapped along the Median Tectonic Line (MTL) which dips approximately 40°N. To understand its structural context and how the MTL functions in this slip-partitioned system, we collected a set of three seismic profiles in the Kii peninsula south of Osaka, using a multi-scale acquisition strategy that provides increasingly fine resolution. To understand its fault kinematics, we analyzed microseismic activity in two locations on the fault, using source data from Japan's Hi-net monitoring network. Structural details suggest that the MTL functioned as a megathrust during subduction of the Cretaceous Sanbagawa HP metamorphic belt. Its current pattern of microseismicity shows that it behaves as a strike-slip fault with no indication of a vertical fault at or around its surface trace. Thus, trench-parallel slip at the Nankai is now accommodated on an inclined fault plane in an unusual form of partitioning. This system appears to have developed out of a two-phase tectonic history in which a thrust structure that formed under initial-phase compressive stresses has been reactivated as a strike-slip fault under subsequent-phase shear stresses. Its unusual kinematics show that shear failure can occur on an existing non-vertical fault plane at a regional scale in preference to the rupture of a new ideal (vertical) fault plane.

To investigate the applicability of frictional reactivation theory to active faults, we evaluated the slip tendency of active faults in Japan. Slip tendency is defined as the ratio of shear stress to the frictional resistance acting on a fault plane. To estimate the stress field near active faults, we determined focal mechanisms for numerous shallow earthquakes in the intraplate region of Japan, using data from dense seismic observation networks. The stress fields were estimated by applying the stress inversion method to the focal mechanisms. We found that most active faults are well oriented with respect to the stress field, having slip tendencies of ≥0.6, which indicates that fault reactivation theory is applicable to active faults, and that the present day tectonic stress field has contributed substantially to the development of active faults. Conversely, several steeply dipping active faults in northeast Japan, as well as the source faults of the 1995 Hyogoken–Nanbu earthquake, are mis-oriented, with slip tendencies of

Dynamin is a mechanochemical GTPase essential for membrane fission during clathrin mediated endocytosis. Dynamin forms washer ring-shaped/helical complexes at the neck of clathrin-coated pits and their structural changes coupled with GTP hydrolysis drive membrane fission. Dynamin and its binding protein amphiphysin cooperatively regulates membrane remodeling during fission, but its precise mechanism remains elusive. In this study, we analyze structural changes of dynamin-amphiphysin complexes during membrane fission using electron microscopy (EM) and high-speed atomic force microscopy (HS-AFM). Interestingly, HS-AFM analyses show that the dynamin-amphiphysin rings are rearranged to form clusters upon GTP hydrolysis and membrane constriction occurs at protein-uncoated regions flanking the clusters. We also show a novel function of amphiphysin in size control of the clusters to enhance biogenesis of endocytic vesicles. Our new approaches using combination of EM and HS-AFM clearly demonstrates dynamics of dynamin-amphiphysin complexes during membrane fission suggesting a novel “clusterase” model of dynamin-mediated membrane fission.

Fluids are thought to play an important role in controlling episodic tremor and slow slip (ETS) in subduction zones. Therefore, constraining the along-dip distribution of fluids is necessary to better understand source mechanism of ETS, and particularly the role played by fluids in ETS generation. Here, we report clear observations of coherent ScSp phases with a dense seismic array in western Shikoku, Japan, where ETS has been most active over the past decade. Using numerical simulations of elastic-wave propagation to reproduce the observed ScSp phases, we demonstrate that, relative to shallower depths, either the Vp/Vs ratio or the thickness of a low-velocity zone (LVZ) within the subducting oceanic crust increases with depth beneath the mantle wedge corner where ETS has been observed. Based on these depth dependences of the structural elements, a wide semi-ductile shear zone appears to be lubricated by high-pressurized fluid in the subducting oceanic crust at ETS source depths, and to be a key factor regulating ETS activity.

The concentrations of organophosphate flame retardants (OPFRs) in the indoor air and dust were measured in 25 unoccupied cars in Japan. In the indoor air of the cars, most OPFRs were neither detected nor found at a concentration lower than the method quantification limit. The highest concentration (1500 ng m−3) was obtained for tris(1-chloro-2-propyl) phosphate (TCIPP). By contrast, many OPFRs were detected in the dust samples collected from the interior of the cars. TCIPP and tris(2-ethylhexyl) phosphate (TEHP) were present at the highest concentrations at 390 μg g−1 (in dust from car seats) and 640 μg g−1 (in dust from car floor mats), respectively. The highest median concentrations (35 μg g−1 for car seats, 53 μg g−1 for car floor mats) were obtained for tris(2-butoxyethyl) phosphate (TBOEP). According to the results of our exposure assessment, the typical exposures to OPFRs via inhalation in car cabins ranged from 9.0×10−4 to 7.8×10−1 ng kg-bw−1 day−1. The typical exposures to OPFRs via dust ingestion ranged from 9.2×10−4 to 8.8×10−1 ng kg-bw−1 day−1. We compared these results with the ref-erence doses for OPFRs and found that, based on cur-rent information about the toxicities of OPFRs, exposure to OPFRs in car cabins via inhalation and dust ingestion is unlikely to have adverse human health effects.

The dynamic triggering of earthquakes is well documented; however, the underlying physical mechanisms remain obscure. Here we analyze the seismicity in northern Nagano, central Japan, following the Tohoku-oki quake, until the occurrence 13 h later of an Mw6.2 local earthquake. We use waveform detection techniques to identify 17 times more earthquakes than those in the Japan Meteorological Agency catalog. The activation of seismicity in the epicentral region of the Mw6.2 event is weak and delayed, culminating with the occurrence of the moderate shock preceded by two small foreshocks. The seismicity activation to the south is shallower, abundant, and starts during the passage of Tohoku-oki surface waves of high dynamic stresses. The early activation occurs in areas of relatively high near-surface fluid temperature, indicating that the dynamic triggering is likely caused by excitation of geothermal crustal fluids. The Mw6.2 Northern Nagano earthquake might have been delay-triggered by fluid migration from a deep source.

After the occurrence of the 2011 magnitude 9 Tohoku earthquake, the seismicity in the overriding plate changed. The seismicity appears to form distinct belts. From the spatiotemporal distribution of hypocenters, we can quantify the evolution of seismicity after the 2011 Tohoku earthquake. In some earthquake swarms near Sendai (Nagamachi-Rifu fault), Moriyoshi-zan volcano, Senya fault, and the Yamagata–Fukushima border (Aizu-Kitakata area, west of Azuma volcano), we can observe temporal expansion of the focal area. This temporal expansion is attributed to fluid diffusion. Observed diffusivity would correspond to the permeability of about 10−15 (m2). We can detect the area from which fluid migrates as a seismic low-velocity area. In the lower crust, we found seismic low-velocity areas, which appear to be elongated along N–S or NE–SW, the strike of the island arc. These seismic low-velocity areas are located not only beneath the volcanic front but also beneath the fore-arc region. Seismic activity in the upper crust tends to be high above these low-velocity areas in the lower crust. Most of the shallow earthquakes after the 2011 Tohoku earthquake are located above the seismic low-velocity areas. We thus suggest fluid pressure changes are responsible for the belts of seismicity.

[1] Active and passive seismic experiments in the Kii Peninsula, southwest Japan, revealed prominent structural features around the segment boundary of a megathrust earthquake associated with the subduction of the Philippine Sea Plate (PHS). A distinct reflection band in the uppermost part of the PHS shows significant lateral variation along its strike. The thicker reflection band, which corresponds to the deeper extension of the fault area of the 1944 Tonankai Earthquake, is interpreted to be a zone of high pore fluid pressure, causing a state of conditionally stable slip on the plate boundary by the reduction in effective normal stress. A thinner reflective band corresponds to the deepest part of the rupture area of the 1946 Nankai earthquake, where plate coupling is stronger due to less effect of fluids. This along-strike structural variation controls the differences in frictional properties and the lateral limit of rupturing along the plate boundary.

[1] Intense swarm-like seismicity associated with shallow normal faulting was induced in Ibaraki and Fukushima prefectures, Japan, following the 2011 Tohoku-Oki earthquake. This seismicity shows a systematic spatiotemporal evolution, but little is known of the heterogeneity in crustal structure in this region, or its influence on the evolution of the seismicity. Here, we elucidate a high-resolution model of crustal structure in this region and determine precise hypocenter locations. Hypocenters in Ibaraki Prefecture reveal a planar earthquake alignment dipping SW at ~45°, whereas those in Fukushima Prefecture show a more complex distribution, consisting of conjugate sets of aligned small earthquakes. On the north of the hypocenter of the largest earthquake in the sequence (the M7.0 Iwaki earthquake), we imaged a high-velocity body at shallow depths that lacks aftershock seismicity. Based on fault source models, the large-slip region of the Iwaki earthquake is situated along a zone that roughly coincides with this high-velocity body. We delineated a separate low-velocity anomaly directly beneath the hypocenter of the Iwaki earthquake, indicating crustal fluids in this region. We hypothesize that strong crust underwent structural failure due to the infiltration of crustal fluids into the seismogenic zone from deeper levels, causing the Iwaki earthquake.

Cancer cell invasion is mediated by actin-based membrane protrusions termed invadopodia. Invadopodia consist of "core" F-actin bundles associated with adhesive and proteolytic machineries promoting cell invasion by degrading extracellular matrix (ECM). Formation of the F-actin core in invadopodia is regulated by various actin-binding proteins including Arp2/3 complex and cortactin. Dynamin GTPase localizes to the invadopodia and is implicated in cancer cell invasion, but its precise role at the invadopodia remained elusive. In this study, we examined the roles of dynamin at the invadopodia of bladder cancer cells. Although all three dynamin isoforms (dynamin1, 2 and 3) are expressed in human bladder cancer cell line T24, only dynamin2 localizes to the invadopodia. Inhibition of dynamin2 function, using either RNA interference (RNAi) or the dynamin specific inhibitor Dynasore, caused defects in invadopodia formation and suppressed invasive activity of T24 bladder cancer cells. Structure-function analysis using dynamin2 deletion fragments identified the proline/arginine-rich domain (PRD) of dynamin2 as indispensable for invadopodia formation and invasiveness of T24 cells. Thus, dynamin2 contributes to bladder cancer invasion by controlling invadopodia formation in bladder cancer cells and may prove a valuable therapeutic target.

Specific mutations in dynamin 2 are linked to Charcot-Marie-Tooth disease (CMT), an inherited peripheral neuropathy. However, the effects of these mutations on dynamin function, particularly in relation to the regulation of the actin cytoskeleton remain unclear. Here, selected CMT-associated dynamin mutants were expressed to examine their role in the pathogenesis of CMT in U2OS cells. Ectopic expression of the dynamin CMT mutants 555Δ3 and K562E caused an approximately 50% decrease in serum stimulation-dependent lamellipodia formation; however, only K562E caused aberrations in the actin cytoskeleton. Immunofluorescence analysis showed that the K562E mutation resulted in the disappearance of radially aligned actin bundles and the simultaneous appearance of F-actin clusters. Live-cell imaging analyses showed F-actin polymers of decreased length assembled into immobile clusters in K562E-expressing cells. The K562E dynamin mutant colocalized with the F-actin clusters, whereas its colocalization with clathrin-coated pit marker proteins was decreased. Essentially the same results were obtained using another cell line, HeLa and NG108-15 cells. The present study is the first to show the association of dynamin CMT mutations with aberrant actin dynamics and lamellipodia, which may contribute to defective endocytosis and myelination in Schwann cells in CMT.

We investigate the detailed distribution of hypocenters and focal mechanisms beneath the Tanzawa Mountains, central Japan, where the Izu-Bonin arc has collided into the central part of the Honshu arc. Remarkable differences are found to exist between the hypocenter distributions in the western and eastern parts. The hypocenters of earthquakes in the eastern part tend to be distributed in a horizontal zone, whereas those in the western part are distributed in a volume. The focal mechanisms in the eastern part are right-lateral reverse faulting mechanisms, and one of the nodal planes is consistent with the geometry of the Philippine Sea (PHS) plate in the region. These results suggest that most earthquakes in the eastern part occur along the upper surface of the subducting PHS plate. In contrast, the focal mechanisms in the western part, especially deep in the western part, exhibit a different feature. The stress states in these two regions are found to be significantly different. The maximum and minimum principal stress axes in the eastern part are slightly inclined, whereas those in the western part are oriented in approximately the vertical and horizontal directions, respectively. The stress field in the eastern part may be caused by a slab pull force induced from the deeper part of the subducted plate.

Seismic noise reveals volcanic plumbing Monitoring the way in which seismic noise passes through Earth's crust after a large earthquake can clarify how volcanoes erupt. Japan has the highest-density seismic network in the world. Brenguier et al. observed reductions in seismic velocity below volcanic regions of Japan from before, to the weeks and months after the 2011 Tohoku-Oki earthquake (see the Perspective by Prejean and Haney). This indicates that pressurized fluids below volcanoes can weaken in response to dynamic stress perturbations. Science , this issue p. 80 ; see also p. 39

Dynamin is a mechanochemical GTPase essential for membrane fission during clathrin-mediated endocytosis. Dynamin forms helical complexes at the neck of clathrin-coated pits and their structural changes coupled with GTP hydrolysis drive membrane fission. Dynamin and its binding protein amphiphysin cooperatively regulate membrane remodeling during the fission, but its precise mechanism remains elusive. In this study, we analyzed structural changes of dynamin-amphiphysin complexes during the membrane fission using electron microscopy (EM) and high-speed atomic force microscopy (HS-AFM). Interestingly, HS-AFM analyses show that the dynamin-amphiphysin helices are rearranged to form clusters upon GTP hydrolysis and membrane constriction occurs at protein-uncoated regions flanking the clusters. We also show a novel function of amphiphysin in size control of the clusters to enhance biogenesis of endocytic vesicles. Our approaches using combination of EM and HS-AFM clearly demonstrate new mechanistic insights into the dynamics of dynamin-amphiphysin complexes during membrane fission., eLife digest The nerve cells that make up a nervous system connect at junctions known as synapses. When a nerve impulse reaches the end of the cell, membrane-bound packages called vesicles fuse with the surface membrane and release their contents to the outside. The contents, namely chemicals called neurotransmitters, then travels across the synapse, relaying the signal to the next cell. Nerve cells can fire many times per second. The membrane from fused vesicles must be retrieved from the surface membrane and recycled to make new vesicles, ready to transmit more signals across the synapse. Many proteins at these sites are involved in folding the fused membrane back into the cell, constricting the opening, and eventually pinching off the new vesicles – a process known as endocytosis. Two proteins named dynamin and amphiphysin cooperate in this process, but their precise mechanism remained elusive. Dynamin is a protein that acts like a motor; it breaks down a molecule called GTP to release energy. Previous studies have seen that dynamin-amphiphysin complexes join end to end to form long helical structures. Takeda et al. have now looked at how the structure of the helices changes during endocytosis. This revealed that the dynamin-amphiphysin helices rearrange to form clusters when the GTP is broken down. Further analysis showed that the folded membrane becomes constricted at regions that are not coated with the clusters of dynamin-amphiphysin helices. Takeda et al. also discovered that amphiphysin controls the size of the clusters to help make the new vesicles more uniform. The gene for dynamin is altered in a number of disorders affecting the nervous system and muscles, including epileptic encephalopathy, Charcot-Marie-Tooth disease and congenital myopathy. Moreover, a neurological disorder characterized by muscle stiffness (known as Stiff-person syndrome) occurs when an individual’s immune system mistakenly attacks the amphiphysin protein. As such, these new findings will not only help scientists to better understand the process of endocytosis, but they will also give new insight into a number of human diseases.