Subsequent Reorganization Research Articles

Temporal requirements of the fragile X mental retardation protein in modulating circadian clock circuit synaptic architecture

Loss of fragile X mental retardation 1 (FMR1) gene function is the most common cause of inherited mental retardation and autism spectrum disorders, characterized by attention disorder, hyperactivity and disruption of circadian activity cycles. Pursuit of effective intervention strategies requires determining when the FMR1 product (FMRP) is required in the regulation of neuronal circuitry controlling these behaviors. In the well-characterized Drosophila disease model, loss of the highly conserved dFMRP causes circadian arrhythmicity and conspicuous abnormalities in the circadian clock circuitry. Here, a novel Sholl Analysis was used to quantify over-elaborated synaptic architecture in dfmr1-null small ventrolateral neurons (sLNvs), a key subset of clock neurons. The transgenic Gene-Switch system was employed to drive conditional neuronal dFMRP expression in the dfmr1-null mutant background in order to dissect temporal requirements within the clock circuit. Introduction of dFMRP during early brain development, including the stages of neurogenesis, neuronal fate specification and early pathfinding, provided no rescue of dfmr1 mutant phenotypes. Similarly, restoring normal dFMRP expression in the adult failed to restore circadian circuit architecture. In sharp contrast, supplying dFMRP during a transient window of very late brain development, wherein synaptogenesis and substantial subsequent synaptic reorganization (e.g. use-dependent pruning) occur, provided strong morphological rescue to reestablish normal sLNvs synaptic arbors. We conclude that dFMRP plays a developmentally restricted role in sculpting synaptic architecture in these neurons that cannot be compensated for by later reintroduction of the protein at maturity.

The interaction of cell‐penetrating peptides with lipid model systems and subsequent lipid reorganization: thermodynamic and structural characterization

Cell-penetrating peptides (CPPs) are cationic peptides that are able to induce cellular uptake and delivery of large and hydrophilic molecules, that otherwise do not cross the plasma membrane of eukaryotic cells. Despite their potential use for gene transfer and drug delivery, the mode of action of CPPs is still mysterious. Nonetheless, the interaction with phospholipid bilayers constitutes the first step in the process. The interaction of two CPPs with distinct charge distribution, penetratin (nonamphipathic) and RL16 (a secondary amphipathic peptide with antimicrobial properties) with lipid membranes was investigated. For this purpose, we employed three independent techniques, comprising (31)P-nuclear magnetic resonance, differential scanning calorimetry (DSC), and plasmon waveguide resonance (PWR) spectroscopy. In view of the cationic nature of the peptides, their interaction and affinity for zwitterionic versus anionic lipids was investigated. Although a strong affinity was observed when negative charged lipids were present, the peptides' thermodynamic behavior on binding to zwitterionic versus anionic lipids and the induced supramolecular structure organization in those lipids was quite different. The study suggests that the amphipathic profile and charge distribution of CPPs strongly influences the perturbation mechanism of the peptide on the bilayer establishing the frontier between a pure CPP and a CPP with antimicrobial properties.

The Changing Structure of Communist Party Membership in Urban China, 1988–2002

This paper examines changes in the membership structure of the Communist Party of China during the 1990s. It concentrates on urban China to investigate the relationship between socioeconomic characteristics of the region (city) and the age, educational, and occupational structures of the regional party. The major findings are as follows. First, the development of marketization has widened opportunities for the younger generation to achieve socioeconomic success outside party membership. Second, the younger generation's incentives for joining the party have consequently been increasingly important determinants of the party's membership structure. Third, the subsequent technocratic reorganization of the urban party seems to have progressed through the conventional bureaucratic-elite path in the government and publicly owned sectors rather than through the newly emerging qualified professional-elite path.

Reorganizing Nursing Work on Surgical Units: A Time-and-Motion Study

A time-and-motion study was conducted in response to perceptions that the surgical nursing staff at a Montreal hospital was spending an excessive amount of time on non-nursing care. A sample of 30 nurse shifts was observed by trained observers who timed nurses' activities for their entire working shift using a hand-held Personal Digital Assistant. Activities were grouped into four main categories: direct patient care, indirect patient care, non-nursing and personal activities. Break and meal times were excluded from the denominator of total worked hours. A total of 201 working hours were observed, an average of 6 hours, 42 minutes per nurse shift. The mean proportions of each nurse shift spent on the main activity categories were: direct care 32.8%, indirect care 55.7%, non-nursing tasks 9.0% and personal 2.5%. Three activities (communication among health professionals, medication verification/preparation and documentation) comprised 78.9% of indirect care time. Greater time on indirect care was associated with work on night shifts and on the short-stay surgical unit. Subsequent work reorganization focused on reducing time spent on communication and medications. The authors conclude that time-and-motion studies are a useful method of monitoring appropriate use of nursing staff, and may provide results that assist in restructuring nursing tasks.

Adsorbate-induced surface reorganization on PtZn electrode

Carbon monoxide oxidation electrocatalysis and the subsequent surface reorganization on an electrochemically prepared PtZn alloy are presented. Zn was electrochemically deposited on a bulk Pt substrate and the alloy was naturally formed. This makes the surface of Zn-modified Pt (or PtZn) electrode rough compared to the surface of the original Pt substrate. CO oxidation catalysis on PtZn was measured and compared to that from Pt with a smooth surface. Although Zn modification did not enhance the catalytic activity compared to Pt, cycling the potential in a CO saturated acid solution appeared to make the PtZn surface smoother and Pt-rich. Oxygen reduction reaction (ORR) catalytic activity was also examined and compared to Pt with equivalent roughness. PtZn showed an enhancement indicating that Zn modification had impact on improving the ORR catalytic activity. From our experimental data, it could also be suggested that the PtZn surface becomes Zn-rich after cycling the potential in an oxygen saturated acidic solution.

A new bathymetric compilation highlighting extensive paleo–ice sheet drainage on the continental shelf, South Georgia, sub‐Antarctica

A grid derived from a new compilation of marine echo‐sounding data sets has allowed us to visualize and map the geomorphology of the entire continental shelf around South Georgia at an unprecedented level of detail. The grid is the first continuous bathymetric data set covering South Georgia to include multibeam swath bathymetry and represent them at a subkilometer resolution. Large and previously undescribed glacially eroded troughs, linked to South Georgia's modern‐day fjords, radiate from the island, marking the former pathways of large outlet glaciers and ice streams. A tectonic or geological influence is apparent for the major troughs, where glaciers have exploited structural weaknesses on the continental block. Bed forms lining the troughs give some first insights into glacial dynamics within the troughs, suggesting arteries of fast flowing ice occupied these topographic depressions in the past and operated over both bedrock and sedimentary substrates. On the outer shelf and within the troughs, large ridges and banks are also common, interpreted as terminal, lateral, and recessional moraines marking former positions of ice sheets on the shelf and their subsequent reorganization during deglaciation. A small trough mouth fan has developed at the mouth of at least one of the cross‐shelf troughs, demonstrating a focused sediment delivery to the margin. Slides and slide scars are also present on parts of the margin, showing that margin stability, perhaps also related to glaciation, has been an important factor in depositional processes on the continental slope. Implications of the new observations are that ice sheets have been more extensive on South Georgia than any previous studies have reported. Their age may date back to late Miocene times, and evolution of the shelf system has probably involved numerous late Cenozoic glacial episodes. However, relatively fresh seafloor geomorphology coupled with evidence from other maritime‐Antarctic islands (Heard Island and Kerguelen Island) indicating extensive glaciation at the Last Glacial Maximum raises the possibility that the extent of sub‐Antarctic glaciation for the Last Glacial period has, until now, been underestimated.

School principals\' perceptions of team management: a multiple case-study of secondary schools

The notion of school management through teams (team management), though not a new phenomenon in South Africa, was formalized after the advent of democracy in 1994 and the subsequent reorganization of the education system. The concept was subsequently fleshed out in official documentation where the composition and roles of school management teams (SMTs) were elaborated upon. The notion of team management is rooted in theories that stress participation, notably site-based (school-based) management, teamwork, and distributed leadership. We report on a study in which the perceptions of secondary school principals, in Grahamstown, South Africa, of team management were explored. The study was interpretive in orientation, and utilized qualitative data gathering techniques in all (ten) of the state-aided secondary schools in Grahamstown in the Eastern Cape province. We found that, while team management was generally welcomed and even celebrated by principals, there were fundamental tensions surrounding principals' understanding of their leadership roles in a team context. We considers the implications of these findings for leadership development in the context of team management.

Detrital zircon evidence from Burma for reorganization of the eastern Himalayan river system

The first <i>in situ</i> Hf and U-Pb isotope analyses of detrital zircons from Upper Miocene sandstone in the Inner-Burma Tertiary Basin, together with data of igneous zircons from the eastern Transhimalayan batholith from southern Tibet to Burma, enable us to study the sedimentary source to sink relation and river evolution around the eastern Himalayas. Among 47 out of 62 dated zircons from the Miocene sandstone that exhibit Cretaceous and Paleogene ²⁰⁶Pb/²³⁸U ages, 24 grains have positive ε_Hf(T) isotope values up to +16. Whilst zircons of such ages are common in the Transhimalayan plutons, those showing high ε_Hf(T) values have been observed so far only in the Gangdese batholith. Our results, therefore, support the notion that by Late Miocene time the Yarlu Tsangpo, which flows past the Gangdese batholith in southeastern Tibet, drained into the Irrawaddy River. We attribute this river routing to not only regional topographic control but also the dextral movement of the Jiali-Gaoligong-Sagaing fault system that appears most active during the Middle Miocene. Subsequent reorganization of these mountain rivers was affiliated with headward erosion of the Brahmaputra River that eventually cut across the Namche Barwa Syntaxis and captured the Yarlu Tsangpo drainage to form the modern eastern Himalayan river system.

Interaction and localization of Necl‐5 and PDGF receptor β at the leading edges of moving NIH3T3 cells: Implications for directional cell movement

It was previously shown that platelet-derived growth factor (PDGF) receptor physically and functionally interacts with integrin alpha(v)beta(3), effectively inducing cell movement. We previously showed that Necl-5, originally identified as a poliovirus receptor, interacts with integrin alpha(v)beta(3) and enhances its clustering and the formation of focal complexes at the leading edges of moving cells, resulting in an enhancement of cell movement. We showed here that Necl-5 additionally interacts with PDGF receptor in NIH3T3 cells and regulates the interaction between PDGF receptor and integrin alpha(v)beta(3), effectively inducing directional cell movement. PDGF receptor co-localized with Necl-5 and integrin alpha(v)beta(3) at peripheral ruffles over lamellipodia, which were formed at the leading edges of moving cells in response to PDGF, but not at the focal complexes under these ruffles, whereas Necl-5 and integrin alpha(v)beta(3) co-localized at these focal complexes. The clustering of these three molecules at peripheral ruffles required the activation of integrin alpha(v)beta(3) by vitronectin and the PDGF-induced activation of the small G protein Rac and subsequent re-organization of the actin cytoskeleton. These results indicate a key role of Necl-5 in directional cell movement by physically and functionally interacting with both integrin alpha(v)beta(3) and PDGF receptor.

NCAM and PSA-NCAM dependent membrane spreading and F-actin reorganization in suspended adhering neural cells

Mediation of synchronous cell-cell interactions by NCAM and PSA-NCAM is examined here in aggregates (monolayers) of C6 polysialylated embryonic neural cells, formed rapidly (within 30 s) in suspension in an ultrasound trap. These cells express all three main isoforms of neural cell adhesion molecule (NCAM). The rate of extension of perimeter contact (i.e., membrane spreading) between closely adjacent cells and the temporal reinforcement of the Filamentous (F)-actin cytoskeleton at those regions were measured. Enzymatic removal of the cell-cell repelling polysialic acid (PSA) increases the rate of NCAM-induced membrane spreading, while removal of NCAM-120 had no detectable effect. Competitive peptide inhibition of the third immunoglobulin domain of NCAM significantly reduced the rate of membrane spreading, while NCAM siRNA transfected cells lost their ability to spread. It is argued that NCAM induced contact is the initial requirement for membrane spreading and facilitates conditions for subsequent cytoskeletal reorganization in these neural cells.

The contribution of synaptic plasticity in the basal ganglia to the processing of visual information

A mechanism for the involvement of the basal ganglia in the processing of visual information, based on dopamine-dependent modulation of the efficiency of synaptic transmission in interconnected parallel associative and limbic cortex-basal ganglia-thalamus-cortex circuits, is proposed. Each circuit consists of a visual or prefrontal area of the cortex connected with the thalamic nucleus and the corresponding areas in different nuclei of the basal ganglia. The circulation of activity in these circuits is supported by the recurrent arrival of information in the thalamus and cortex. Dopamine released in response to a visual stimulus modulates the efficiencies of "strong" and "weak" corticostriatal inputs in different directions, and the subsequent reorganization of activity in the circuit leads to disinhibition (inhibition) of the activity of those cortical neurons which are "strongly" ("weakly") excited by the visual stimulus simultaneously with dopaminergic cells. The pattern in each cortical area is the neuronal reflection of the properties of the visual stimulus processed by this area. Excitation of dopaminergic cells by the visual stimulus via the superior colliculi requires parallel activation of the disinhibitory input to the superior colliculi via the thalamus and the "direct" pathway" in the basal ganglia. The prefrontal cortex, excited by the visual stimulus via the mediodorsal nucleus of the thalamus, mediates the descending influence on the activity of dopaminergic cells, simultaneously controlling dopamine release in different areas of the striatum and thus facilitating the mutual selection of neural reflections of the individual properties of the visual stimulus and their binding into an integral image.

Lake Agassiz Final drainage event in the northwest North Atlantic

The 8.2 ka “climate” event recorded in Greenland ice cores is subject of debates with respect to causal linkage with a collapse of the Atlantic Meridional Overturning due to the drainage of the late‐glacial lake Agassiz. Here, we present records from the NW North Atlantic, down‐current the flood discharge route, showing that the 9.5–8 ka interval was marked by a succession of events. The drainage itself corresponds to a twin‐layer of carbonate‐rich turbidites deposited within the calibrated 8.35–8.5 ka interval. Proxies of sea‐surface and deep‐current conditions do not indicate significant concomitant changes in the NW North Atlantic. The dataset, however, supports the concept that the 8.2 ka “climate” event may represent one of the manifestations of climate instability during an interval with major changes of land drainage in NE America, due to the collapse of the Laurentide Ice Sheet, subsequent fast sea level rise and large scale reorganization of the North Atlantic thermohaline circulation pattern.

Requirement of Ca2+ influx- and phosphatidylinositol 3-kinase-mediated m-calpain activity for shear stress-induced endothelial cell polarity

Proteolytic activity in sheared human umbilical vein endothelial cells (HUVECs) was measured using a fluorogenic substrate and laser scanning confocal microscopy to clarify the key role of an intracellular Ca(2+)-sensitive protease, calpain, in these cells in response to shear stress. Within physiological shear range, activity in the cells was enhanced in shear-dependent fashion. Short interfering RNA-induced silencing of m-calpain, but not of micro-calpain, suppressed the activity. Either removal of extracellular Ca(2+) or application of an intracellular Ca(2+) chelator (BAPTA/AM) or nonselective cation channel blocker (Gd(3+)) reduced proteolytic activity. Furthermore, activity was suppressed by phosphatidylinositol bisphosphate (PIP(2)) chelator (neomycin) or phosphatidylinositol 3-kinase (PI3K) inhibitor (LY294002); in contrast, activity, which was partially inhibited by ERK kinase inhibitor (U0126, PD98059), was unaffected by PLC inhibitor (U73122). Moreover, Akt phosphorylation downstream of PI3K, which was elicited by shear, was attenuated by neomycin but not by calpain inhibitor (calpeptin). Following assessment of shear stress-induced focal adhesion (FA) and cytoskeletal dynamics using interference reflection/green fluorescence protein-actin microscopy, we found that either calpain or PI3K inhibition impaired shear stress-induced polarization of FAs via stabilization of FA structures. Additionally, HUVEC alignment and cytoskeletal remodeling, which was accompanied by calpain-mediated cleavage of vinculin and talin, were also elicited by prolonged application of shear and impaired by m-calpain knockdown. Thus, these results revealed that physiological shear stress elicits Ca(2+) influx-sensitive activation of m-calpain in HUVECs. This activity is facilitated primarily through the PI3K pathway; furthermore, it is essential for subsequent FA reorganization and cell alignment under shear conditions.

Inactivation of Cdc42 Is Necessary for Depolymerization of Phagosomal F-Actin and Subsequent Phagosomal Maturation

Phagocytosis is a complex process involving the activation of various signaling pathways, such as the Rho GTPases, and the subsequent reorganization of the actin cytoskeleton. In neutrophils, Rac and Cdc42 are activated during phagocytosis but less is known about the involvement of these GTPases during the different stages of the phagocytic process. The aim of this study was to elucidate the role of Cdc42 in phagocytosis and the subsequent phagosomal maturation. Using a TAT-based protein transduction technique, we introduced dominant negative and constitutively active forms of Cdc42 into neutrophil-like HL60 (human leukemia) cells that were allowed to phagocytose IgG-opsonized yeast particles. Staining of cellular F-actin in cells transduced with constitutively active Cdc42 revealed that the activation of Cdc42 induced sustained accumulation of periphagosomal actin. Moreover, the fusion of azurophilic granules with the phagosomal membrane was prevented by the accumulated F-actin. In contrast, introducing dominant negative Cdc42 impaired the translocation per se of azurophilic granules to the periphagosomal area. These results show that efficient phagosomal maturation and the subsequent eradication of ingested microbes in human neutrophils is dependent on a strictly regulated Cdc42. To induce granule translocation, Cdc42 must be in its active state but has to be inactivated to allow depolymerization of the F-actin cage around the phagosome, a process essential for phagolysosome formation.

Preferential Phosphorylation of Focal Adhesion Kinase Tyrosine 861 Is Critical for Mediating an Anti-apoptotic Response to Hyperosmotic Stress

The results presented here demonstrate that focal adhesion kinase (FAK) Tyr-861 is the predominant tyrosine phosphorylation site stimulated by hyperosmotic stress in a variety of cell types, including epithelial cell lines (ileum-derived IEC-18, colon-derived Caco2, and stomach-derived NCI-N87), FAK null fibroblasts re-expressing FAK, and Src family kinase triple null fibroblasts (SYF cells) in which c-Src has been restored (YF cells). We show that hyperosmotic stress-stimulated FAK phosphorylation in epithelial cells is inhibited by Src family kinase inhibitors PP2 and SU6656 and that it does not occur in SYF cells. Unexpectedly, hyperosmotic stress-induced phosphorylation of FAK at Tyr-397, Tyr-576, and most dramatically at Tyr-861 was completely insensitive to the F-actin-disrupting agents, latrunculin A and cytochalasin D. Finally, we show that in FAK null cells exposed to hyperosmotic stress or growth factor withdrawal, re-expression of wild type FAK restored cell survival, whereas re-expression of FAK mutated from tyrosine to phenylalanine at position 861 (FAKY861F) did not. Our results indicate that FAK Tyr-861 phosphorylation is required for mammalian cell survival of hyperosmotic stress. Furthermore, the results suggest that FAK is an upstream regulator (rather than downstream effector) of F-actin reorganization in response to hyperosmotic stress. We propose that FAK/c-Src bipartite enzyme is a sensor of cytoplasmic shrinkage, and that the phosphorylation on FAK Tyr-861 by Src and subsequent reorganization of F-actin can initiate an anti-apoptotic signaling pathway that protects cells from hyperosmotic stress.

Transient microglial and prolonged astroglial upregulation of osteopontin following transient forebrain ischemia in rats

Osteopontin (OPN) is an adhesive glycoprotein linked to a variety of pathophysiological processes, with neuroprotective properties in ischemic injury. We examined the postischemic expression and localization of OPN in the rat brain after transient forebrain ischemia. The semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis showed that OPN expression in the hippocampal CA1 region was biphasic, peaking at day 3 after reperfusion and again between days 14 and 28. The two phases of OPN induction occurred in a time- and cell-dependent manner in the ischemic hippocampus. OPN mRNA expression in activated microglia was first induced 1 day after reperfusion, reached a peak at 3 days, and returned to basal levels by 7 days. In contrast, OPN expression in reactive astrocytes was first induced by 10 days after reperfusion in the hippocampal CA1. Astroglial OPN expression further increased, reaching a peak at day 14 and was maintained up to day 28, the latest time point we examined. OPN immunoreactivity in the ischemic hippocampus matched the mRNA induction patterns. OPN protein was first localized in the astroglial cytoplasm and later in the extracellular matrix of the hippocampal CA1. The temporal and cellular patterns of OPN induction in the ischemic hippocampus suggest a multifunctional capacity in the pathogenesis of ischemic injury, with the increased OPN production and secretion by reactive astrocytes being involved in subsequent tissue repair and reorganization.

Rac Activity Is Polarized and Regulates Meiotic Spindle Stability and Anchoring in Mammalian Oocytes

Mammalian meiotic divisions are asymmetrical and generate a large oocyte and two small polar bodies. This asymmetry results from the anchoring of the meiotic spindle to the oocyte cortex and subsequent cortical reorganization, but the mechanisms involved are poorly understood. We investigated the role of Rac in oocyte meiosis by using a fluorescent reporter for Rac-GTP. We find that Rac-GTP is polarized in the cortex overlying the meiotic spindle. Polarization of Rac activation occurs during spindle migration and is promoted by the proximity of chromatin to the cortex. Inhibition of Rac during oocyte maturation caused a permanent block at prometaphase I and spindle elongation. In metaphase II-arrested oocytes, Rac inhibition caused the spindle to detach from the cortex and prevented polar body emission after activation. These results demonstrate that Rac-GTP plays a major role in oocyte meiosis, via the regulation of spindle stability and anchoring to the cortex.

Impact of acute and enduring volume overload on mechanotransduction and cytoskeletal integrity of canine left ventricular myocardium

It is poorly understood how mechanical stimuli influence in vivo myocardial remodeling during chronic hemodynamic overload. Combined quantitation of ventricular mechanics and expression of key proteins involved in mechanotransduction can improve fundamental understanding. Adult anesthetized dogs (n = 20) were studied at sinus rhythm (SR) and 0, 3, 10, and 35 days of complete atrioventricular block (AVB). Serial left ventricular (LV) myofiber mechanics were measured. Repeated LV biopsies were analyzed for mRNA and/or protein expression of beta(1D)-integrin, melusin, Akt, GSK3beta, muscle LIM protein (MLP), four-and-a-half LIM protein 2 (fhl2), desmin, and calpain. Upon AVB, increased ejection strain (0.29 +/- 0.01 vs. 0.13 +/- 0.02, SR) and end-diastolic stress (4.8 +/- 1.1 vs. 2.7 +/- 0.4 kPa) dominated mechanical changes. Brain natriuretic peptide plasma levels were correspondingly high (33 +/- 4 vs. 19 +/- 1 pg/ml, SR). beta(1D)-Integrin protein expression increased chronically after AVB. Melusin was temporarily overexpressed (+33 +/- 9%, 3 days AVB vs. SR), followed by elevated ratios of phosphorylated (P)-Akt to Akt and P-GSK3beta to GSK3beta (+26 +/- 6% and +30 +/- 8% at 10 days AVB vs. SR). These changes corresponded to peak hypertrophic growth at 3 to 10 days. MLP increased gradually to maxima at chronic AVB (+36 +/- 7%). In contrast, fhl2 (-22 +/- 3%, 3 days) and desmin (-30 +/- 9%, 10 days AVB) transiently declined but recovered at chronic AVB. Calpain protein expression remained unaltered. In conclusion, volume overload after AVB causes a transient compromise of cytoskeletal integrity based, at least partly, on transcriptional downregulation. Subsequent cytoskeletal reorganization coincides with the upregulation of melusin, P-Akt, P-GSK3beta, and MLP, indicating a strong drive to compensated hypertrophy.

CD98 Activation Increases the Invasion of Human Breast Carcinoma MCF-7 Cells

CD98, a disulfide-linked 125-kDa heterodimeric type II transmembrane glycoprotein, regulates the func-tions of β₁ integrin, suggesting that it may play a role in tumor cell invasion. In this study, the effects of CD98 signaling on the adhesion and invasion of tumor cells were investigated. The expression of CD98 on MCF-7 human breast carcinoma cells was confirmed by immunohistochemistry. The effects of CD98 activation on the adhesion to extracellular matrix (ECM) and invasion of MCF-7 cells were determined by adhesion assay and cell invasion assay. Dominant negative forms of focal adhesion kinase (FAK) were transiently transfected into MCF-7 cells using liposome reagents. CD98 stimulation increased the adhesion of MCF-7 cells to fibronectin, laminin and collagen IV. Activation of CD98 augmented the invasion rate of MCF-7 cells through ECM. EDTA or a function-blocking anti-β₁ integrin mAb suppressed the effect of CD98 on invasiveness. Inhibition of phosphorylation of FAK by PP2, an inhibitor of Src family kinase, reduced CD98-induced invasion of MCF-7 cells. This result was confirmed by over-expression of dominant negative forms of FAK. In addition, cytochalasin D or phalloidin inhibited CD98-mediated induction of tumor cell invasion. Inhibitory effects of PP2, cytochalasin D or phalloidin on CD98-stimulated invasion of MCF-7 cells were diminished by pretreatment of cells with Mn??, which is shown to induce conformational change of β₁ intgerin. These results provide the first evidence that CD98 activation increases tumor cell invasion by activating β₁ integrin affinity, and that FAK phosphorylation and subsequent cytoskeletal reorganization may be essential for CD98-mediated regulation of cell motility.

A hypothetical role of cortico-basal ganglia-thalamocortical loops in visual processing

The goal of the present work was to define the mechanisms underlying the contribution of sensory and limbic cortico-basal ganglia-thalamocortical loops to visual processing and its attentional modulation. We proposed that visual processing is promoted by dopamine-dependent long-term modifications of synaptic transmission in the basal ganglia that favour a selection of neocortical patterns representing a visual stimulus. This selection is the result of the opposite sign of modulation of strong and weak cortico-basal ganglia inputs and subsequent activity reorganization in each loop. Reorganization leads to disinhibition/inhibition of cortical neurons strongly/weakly excited by stimulus during dopamine release. Recruitment of the thalamo-basal ganglia-collicular pathway is proposed to be necessary for stimulus-evoked dopamine release that underlies bottom-up attentional effects. Visual excitation of the prefrontal cortex and hippocampus (via the thalamus), their cooperation in control of the basal ganglia and dopaminergic cell firing, and simultaneous modulation of activity in diverse cortico-basal ganglia-thalamocortical loops is proposed to underlie top-down attentional effects. It follows from our model that only those components of cortical responses can be modulated by attention, whose onset exceeds the latency of visual responses of dopaminergic cells (50–110 ms). This and other consequences of the model are in accordance with known experimental data.