bluuebunny/crossref_metadata_2025 huggingface dataset:
Roles of microtubules, cell polarity and adhesion in electric-field-mediated motility of 3T3 fibroblasts
Authors: Finkelstein Erik , Chang Winston , Chao P.-H. Grace , Gruber Dorota , Minden Audrey , Hung Clark T. , Bulinski J. Chloë
Published: March 2004

Direct-current electric fields mediate motility (galvanotaxis) of many cell types. In 3T3 fibroblasts, electric fields increased the proportion, speed and cathodal directionality of motile cells. Analogous to fibroblasts' spontaneous migration, we initially hypothesized that reorientation of microtubule components modulates galvanotaxis. However, cells with intact microtubules did not reorient them in the field and cells without microtubules still migrated, albeit slowly, thus disproving the hypothesis. We next proposed that, in monolayers wounded and placed in an electric field, reorientation of microtubule organizing centers and stable, detyrosinated microtubules towards the wound edge is necessary and/or sufficient for migration. This hypothesis was negated because field exposure mediated migration of unoriented, cathode-facing cells and curtailed migration of oriented, anode-facing cells. This led us to propose that ablating microtubule detyrosination would not affect galvanotaxis. Surprisingly, preventing microtubule detyrosination increased motility speed, suggesting that detyrosination inhibits galvanotaxis. Microtubules might enhance adhesion/de-adhesion remodeling during galvanotaxis; thus, electric fields might more effectively mediate motility of cells poorly or dynamically attached to substrata. Consistent with this hypothesis, incompletely spread cells migrated more rapidly than fully spread cells. Also, overexpression of PAK4, a Cdc42-activated kinase that decreases adhesion, enhanced galvanotaxis speed, whereas its lack decreased speed. Thus, electric fields mediate fibroblast migration via participation of microtubules and adhesive components, but their participation differs from that during spontaneous motility.
Developmental-stage-specific triacylglycerol biosynthesis, degradation and trafficking as lipid bodies inPlasmodium falciparum-infected erythrocytes
Authors: Palacpac Nirianne Marie Q. , Hiramine Yasushi , Mi-ichi Fumika , Torii Motomi , Kita Kiyoshi , Hiramatsu Ryuji , Horii Toshihiro , Mitamura Toshihide
Published: March 2004

Triacylglycerol (TAG) serves as a major energy storage molecule in eukaryotes. In Plasmodium, however, this established function of TAG appears unlikely, despite detecting previously considerable amount of TAG associated with intraerythrocytic parasites, because plasmodial cells have very little capacity to oxidize fatty acids. Thus, it is plausible that TAG and its biosynthesis in Plasmodium have other functions. As a first step in understanding the biological significance of TAG and its biosynthesis to the intraerythrocytic proliferation of Plasmodium falciparum, we performed detailed characterization of TAG metabolism and trafficking in parasitized erythrocyte. Metabolic labeling using radiolabeled-oleic and palmitic acids in association with serum albumin, which have been shown to be among the serum essential factors for intraerythrocytic proliferation of P. falciparum, revealed that accumulation of TAG was strikingly pronounced from trophozoite to schizont, whereas TAG degradation became active from schizont to segmented schizont; the consequent products, free fatty acids, were released into the medium during schizont rupture and/or merozoite release. These results were further supported by visualization of lipid bodies through immunofluorescence and electron microscopy. At the schizont stages, there is some evidence that the lipid bodies are partly localized in the parasitophorous vacuole. Interestingly, the discrete formation and/or trafficking of lipid bodies are inhibited by brefeldin A and trifluoperazine. Inhibition by trifluoperazine hints at least that a de novo TAG biosynthetic pathway via phosphatidic acid contributes to lipid body formation. Indeed, biochemical analysis reveals a higher activity of acyl-CoA:diacylglycerol acyltransferase, the principal enzyme in the sn-glycerol-3-phosphate pathway for TAG synthesis, at trophozoite and schizont stages. Together, these results establish that TAG metabolism and trafficking in P. falciparum-infected erythrocyte occurs in a stage-specific manner during the intraerythrocytic cycle and we propose that these unique and dynamic cellular events participate during schizont rupture and/or merozoite release.
Trophic signals acting via phosphatidylinositol-3 kinase are required for normal pre-implantation mouse embryo development
Authors: Lu D. P. , Chandrakanthan V. , Cahana A. , Ishii S. , O'Neill C.
Published: March 2004

The growth and survival of the preimplantation mammalian embryo may be regulated by several autocrine trophic factors that have redundant or overlapping actions. One of the earliest trophic factors to be produced is embryo-derived platelet-activating factor (1-O-alky-2-acetyl-sn-glyceryl-3-phosphocholine). The addition of platelet-activating factor to embryo culture media exerted a trophic effect, but structurally related lipids (3-O-alky-2-acetyl-sn-glyceryl-1-phosphocholine, 1-O-alky-sn-glyceryl-3-phosphocholine, octadecyl-phosphocholine) had no effect. Platelet-activating factor induced a pertussis toxin-sensitive [Ca2+]i transient in two-cell embryos that did not occur in platelet-activating factor-receptor null (Pafr–/–) genotype embryos. Fewer Pafr–/– mouse zygotes developed to the blastocyst stage in vitro compared with Pafr+/+ zygotes (P<0.02), those that developed to blastocysts had fewer cells (P<0.001) and more cells with fragmented nuclei (P<0.001). The inhibition of 1-O-phosphatidylinositol 3-kinase (LY294002 (3 μM and 15 μM) and wortmannin (10 nM and 50 nM)) caused a dose-dependent inhibition of platelet-activating factor-induced [Ca2+]i transients (P<0.001). The two-cell embryo expressed 1-O-phosphatidylinositol 3-kinase catalytic subunits p110α, β, γ and δ, and regulatory subunits p85α and β. LY294002 and wortmannin each caused a significant reduction in the proportion of embryos developing to the morula and blastocyst stages in vitro, reduced the number of cells within each blastocyst, and significantly increased the proportion of cells in blastocysts with fragmented nuclei. The results indicate that embryo-derived platelet-activating factor (and other embryotrophic factors) act through its membrane receptor to enhance embryo survival through a 1-O-phosphatidylinositol 3-kinase-dependent survival pathway.
CRM1 and Ran are present but a NES-CRM1-RanGTP complex is not required in Balbiani ring mRNP particles from the gene to the cytoplasm
Authors: Zhao Jian , Jin Shao-Bo , Wieslander Lars
Published: March 2004

Messenger RNA is formed from precursors known as pre-mRNA. These precursors associate with proteins to form pre-mRNA-protein (pre-mRNP) complexes. Processing machines cap, splice and polyadenylate the pre-mRNP and in this way build the mRNP. These processing machines also affect the export of the mRNP complexes from the nucleus to the cytoplasm. Export to the cytoplasm takes place through a structure in the nuclear membrane called the nuclear pore complex (NPC). Export involves adapter proteins in the mRNP and receptor proteins that bind to the adapter proteins and to components of the NPC. We show that the export receptor chromosomal region maintenance protein 1 (CRM1), belonging to a family of proteins known as importin-β-like proteins, binds to gene-specific Balbiani ring (BR) pre-mRNP while transcription takes place. We also show that the GTPase known as Ran binds to BR pre-mRNP, and that it binds mainly in the interchromatin. However, we also show using leptomycin B treatment that a NES-CRM1-RanGTP complex is not essential for export, even though both CRM1 and Ran accompany the BR mRNP through the NPC. Our results therefore suggest that several export receptors associate with BR mRNP and that these receptors have redundant functions in the nuclear export of BR mRNP.
The N-terminus of the long MLCK induces a disruption in normal spindle morphology and metaphase arrest
Authors: Dulyaninova Natalya G. , Patskovsky Yury V. , Bresnick Anne R.
Published: March 2004

We have shown previously that only the long myosin light chain kinase (MLCK), which is the predominant MLCK isoform expressed in nonmuscle cells, localizes to the cleavage furrow. To further examine the in vivo localization of the long MLCK in HeLa cells and the mechanisms responsible for kinase targeting during the cell cycle, we examined the distribution of the endogenous kinase and constructed green fluorescent protein (GFP) fusions of long HeLa MLCK truncations. A GFP fusion containing the N-terminal IgG domain and the five DXR motifs localized to stress fibers during interphase and the cleavage furrow during mitosis. Although individual fusions of the five DXRs and IgG domain both independently localized to stress fibers, only the five DXRs demonstrated a cortical localization in mitotic cells. Thus, robust targeting of the long MLCK to the cleavage furrow required the five DXRs and additional sequences from the IgG domain. Expression of the IgG domain alone or with five DXRs increased the number of multinucleate cells tenfold, whereas expression of the five DXRs or GFP had no effect. Furthermore, expression of the IgG domain alone or with five DXRs disrupted normal spindle morphology during mitosis. Extended astral microtubules and increased bundling of kinetochore microtubules, and spindle pole fragmentation were detected in mitotic cells. These microtubule defects were associated with abnormalities in metaphase chromosome alignment and a subsequent metaphase arrest caused by activation of the spindle assembly checkpoint at the kinetochores of mono-oriented chromosomes. Together, these results suggest that MLCK has an unexpected regulatory function during mitosis.
An alternative form of paraptosis-like cell death, triggered by TAJ/TROY and enhanced by PDCD5 overexpression
Authors: Wang Ying , Li Xianting , Wang Lu , Ding Peiguo , Zhang Yingmei , Han Wenling , Ma Dalong
Published: March 2004

Accumulating reports demonstrate that apoptosis does not explain all the forms of programmed cell death (PCD), particularly in individual development and neurodegenerative disease. Recently, a novel type of PCD, designated `paraptosis', was described. Here, we show that overexpression of TAJ/TROY, a member of the tumor necrosis factor receptor superfamily, induces non-apoptotic cell death with paraptosis-like morphology in 293T cells. Transmission electron microscopy studies reveal extensive cytoplasmic vacuolation and mitochondrial swelling in some dying cells and no condensation or fragmentation of the nuclei. Characteristically, cell death triggered by TAJ/TROY was accompanied by phosphatidylserine externalization, loss of the mitochondrial transmembrane potential and independent of caspase activation. In addition, TAJ/TROY suppressed clonogenic growth of HEK293 and HeLa cells. Interestingly, overexpression of Programmed cell death 5 (PDCD5), an apoptosis-promoting protein, enhanced TAJ/TROY-induced paraptotic cell death. Moreover, cellular endogenous PDCD5 protein was significantly upregulated in response to TAJ/TROY overexpression. These results provide novel evidence that TAJ/TROY activates a death pathway distinct from apoptosis and that PDCD5 is an important regulator in both apoptotic and non-apoptotic PCD.
Contractile filament architecture and force transmission in swine airway smooth muscle
Authors: Kuo Kuo-Hsing , Seow Chun Y.
Published: March 2004

It is well known that the cyclic interaction of myosin cross bridges with actin filaments is responsible for force and shortening generation in smooth muscle. The intracellular organization of contractile filaments, however, is still poorly understood. Here, we show electron microscopic and functional evidence that contractile filaments in airway smooth muscle lie parallel to the longitudinal axis of the cell bundle, in contrast to the obliquely arranged filaments depicted in conventional models. The parallel arrangement of contractile filaments is maintained despite the fact that individual cells are spindle-shaped. This is accomplished through filament attachment to membrane-associated dense plaques that are in turn connected to similar structures on neighboring cells. Intracellularly, the parallel arrangement is maintained despite the centrally located nucleus. This is accomplished by attachment of actin filaments to the nuclear envelope and making the nucleus a force transmitting structure. The results suggest that smooth muscle cells in tissue form a mechanical syncytium and are able to function properly only as a group.
Deregulation of Flk-1/vascular endothelial growth factor receptor-2 in fibroblast growth factor receptor-1-deficient vascular stem cell development
Authors: Magnusson Peetra , Rolny Charlotte , Jakobsson Lars , Wikner Charlotte , Wu Yan , Hicklin Daniel J. , Claesson-Welsh Lena
Published: March 2004

We have employed embryoid bodies derived from murine embryonal stem cells to study effects on vascular development induced by fibroblast growth factor (FGF)-2 and FGF receptor-1, in comparison to the established angiogenic factor vascular endothelial growth factor (VEGF)-A and its receptor VEGF receptor-2. Exogenous FGF-2 promoted formation of morphologically distinct, long slender vessels in the embryoid bodies, whereas VEGF-A-treated bodies displayed a compact plexus of capillaries. FGF-2 stimulation of embryonal stem cells under conditions where VEGF-A/VEGFR-2 function was blocked, led to formation of endothelial cell clusters, which failed to develop into vessels. FGFR-1-/- embryoid bodies responded to VEGF-A by establishment of the characteristic vascular plexus, but FGF-2 had no effect on vascular development in the absence of FGFR-1. The FGFR-1-/- embryoid bodies displayed considerably increased basal level of vessel formation, detected by immunohistochemical staining for platelet-endothelial cell adhesion molecule (PECAM)/CD31. This basal vascularization was blocked by neutralizing antibodies against VEGFR-2 or VEGF-A and biochemical analyses indicated changes in regulation of VEGFR-2 in the absence of FGFR-1 expression. We conclude that VEGF-A/VEGFR-2-dependent vessel formation occurs in the absence of FGF-2/FGFR-1, which, however, serve to modulate vascular development.
Bub1 is required for kinetochore localization of BubR1, Cenp-E, Cenp-F and Mad2, and chromosome congression
Authors: Johnson Victoria L. , Scott Maria I. F. , Holt Sarah V. , Hussein Deema , Taylor Stephen S.
Published: March 2004

During mitosis, the recruitment of spindle-checkpoint-associated proteins to the kinetochore occurs in a defined order. The protein kinase Bub1 localizes to the kinetochore very early during mitosis, followed by Cenp-F, BubR1, Cenp-E and finally Mad2. Using RNA interference, we have investigated whether this order of binding reflects a level of dependency in human somatic cells. Specifically, we show that Bub1 plays a key role in the assembly of checkpoint proteins at the kinetochore, being required for the subsequent localization of Cenp-F, BubR1, Cenp-E and Mad2. In contrast to studies in Xenopus, we also show that BubR1 is not required for kinetochore localization of Bub1. Repression of Bub1 increases the number of cells with lagging chromosomes at metaphase, suggesting that Bub1 plays a role in chromosome congression. However, repression of Bub1 does not appear to compromise spindle checkpoint function either during normal mitosis or in response to spindle damage. This raises the possibility that, in the absence of Bub1, other mechanisms contribute to spindle checkpoint function.
Microtubules continuously dictate distribution of actin filaments and positioning of cell cleavage in grasshopper spermatocytes
Authors: Alsop G. Bradley , Zhang Dahong
Published: March 2004

We systematically examined the impact of microtubules on distribution of actin filaments and positioning of cell cleavage using micromanipulation to progressively alter the symmetric distribution of spindle microtubules in grasshopper spermatocytes. The initial microtubule asymmetry was induced by placing a single chromosome at one spindle pole using a microneedle, which facilitates regional assembly of spindle microtubules. We augmented chromosome-induced microtubule asymmetry by further removing the aster from the achromosomal pole, producing unichromosome-bearing monopolar spindles. We created the highest spindle asymmetry by cutting early anaphase cells in two, each containing a full set of segregating chromosomes in a half-spindle. We demonstrate that the location of the spindle midzone, distribution of actin filaments, and position of cell cleavage depend on the amount of microtubule asymmetry generated, shifting up to 48.6±3.8% away from the spindle equator in cut cells. The positional shift is dynamic, changing incessantly as spindle microtubules reorganize during cytokinesis. These results suggest that microtubules continuously dictate the distribution of actin filaments and positioning of cell cleavage in grasshopper spermatocytes.
Dynamics of novel feet of Dictyostelium cells during migration
Authors: Uchida Kazuhiko S. K. , Yumura Shigehiko
Published: March 2004

We observed the dynamics of actin foci in live Dictyostelium cells expressing GFP-actin. Actin foci were dynamic structures, but they were fixed on the substratum during cell migration. Interference reflection microscopy revealed that the ventral cell membrane was closer to the substratum at sites of actin foci. Furthermore, some actin foci were incorporated into the retraction fibers, ripped off from the cells and eventually shed on the substratum after the cells moved away. The velocity of the cells was inversely proportional to the number of actin foci. Measurement of traction force using a silicone substratum demonstrated that the traction force was transmitted to the substratum through actin foci. Taken together, several lines of evidence strongly suggest that actin foci function as the active `feet' of Dictyostelium cells. We also found evidence suggesting that changing step is regulated in a coordinated manner during cell migration. Possible mechanisms by which these cells migrate across substrata are discussed in this context.
p130Cas interacts with estrogen receptor α and modulates non-genomic estrogen signaling in breast cancer cells
Authors: Cabodi Sara , Moro Laura , Baj Germano , Smeriglio Monica , Di Stefano Paola , Gippone Silvana , Surico Nicola , Silengo Lorenzo , Turco Emilia , Tarone Guido , Defilippi Paola
Published: March 2004

Steroid hormones bind to their receptors and trans-activate target genes. Rapid non-genomic action of steroid hormones has been proposed in addition to the one at the genomic level. Estrogen has been described to activate c-Src kinase and this activation has been shown to be responsible for estrogen-dependent mitogenicity. A major substrate of c-Src kinase activity is the cytoskeletal protein p130Cas, originally identified in v-Src-transformed cells. We show that in the human breast carcinoma T47D cells, upon estrogen treatment, p130Cas rapidly and transiently associates with the estrogen receptor α in a multi-molecular complex containing the c-Src kinase and the p85 subunit of PI 3-kinase. Association of p130Cas with the estrogen receptor α occurs within 3 minutes of estrogen treatment and is dependent on c-Src kinase activation. Transient overexpression of p130Cas in T47D cells increases estrogen-dependent Src kinase and Erk1/2 MAPKs activities and accelerates their kinetics of stimulation. A similar effect was detected on estrogen-dependent cyclin D1 expression, suggesting a role for p130Cas in regulating estrogen-dependent cell cycle progression. Double-stranded small RNA interference (siRNA) by silencing endogenous p130Cas protein, was sufficient to inhibit estrogen-dependent Erk1/2 MAPKs activity and cyclin D1 induction, demonstrating the requirement of p130Cas in such events. Therefore, our data show that the adaptor protein p130Cas associates with the estrogen receptor transducing complex, regulating estrogen-dependent activation of c-Src kinase and downstream signaling pathways.
The EBP50-moesin interaction involves a binding site regulated by direct masking on the FERM domain
Authors: Finnerty Casey M. , Chambers David , Ingraffea Janet , Faber H. Richard , Karplus P. Andrew , Bretscher Anthony
Published: March 2004

Members of the ezrin-radixin-moesin (ERM) protein family serve as regulated microfilament-membrane crosslinking proteins that, upon activation, bind the scaffolding protein ERM-phosphoprotein of 50 kDa (EBP50). Here we report a 3.5 Å resolution diffraction analysis of a complex between the active moesin N-terminal FERM domain and a 38 residue peptide from the C terminus of EBP50. This crystallographic result, combined with sequence and structural comparisons, suggests that the C-terminal 11 residues of EBP50 binds as an α-helix at the same site occupied in the dormant monomer by the last 11 residues of the inhibitory moesin C-terminal tail. Biochemical support for this interpretation derives from in vitro studies showing that appropriate mutations in both the EBP50 tail peptide and the FERM domain reduce binding, and that a peptide representing just the C-terminal 14 residues of EBP50 also binds to moesin. Combined with the recent identification of the I-CAM-2 binding site on the ERM FERM domain (Hamada, K., Shimizu, T., Yonemura, S., Tsukita, S., and Hakoshima, T. (2003) EMBO J. 22, 502-514), this study reveals that the FERM domain contains two distinct binding sites for membrane-associated proteins. The contribution of each ligand to ERM function can now be dissected by making structure-based mutations that specifically affect the binding of each ligand.
Cdc42 - the centre of polarity
Authors: Etienne-Manneville Sandrine
Published: March 2004

All cell types polarize, at least transiently, during division or to generate specialized shapes and functions. This capacity extends from yeast to mammals, and it is now clear that many features of the molecular mechanisms controlling polarization are conserved in all eukaryotic cells. At the centre of the action is Cdc42, a small GTPase of the Rho family. Its activity is precisely controlled both temporally and spatially, and this can be achieved by a wide variety of extracellular cues in multicellular organisms. Moreover, although the functional characteristics of cell polarity are extremely variable (depending on the cell type and the biological context), Cdc42 has an amazing capacity to co-ordinate the control of multiple signal transduction pathways.
Designing biosensors for Rho family proteins — deciphering the dynamics of Rho family GTPase activation in living cells
Authors: Pertz Olivier , Hahn Klaus M.
Published: March 2004

Rho family GTPases are molecular switches that couple changes in the extracellular environment to intracellular signal transduction pathways. Their ability to regulate behaviors such as cell motility suggests very tight kinetic and spatial control of their activity, which is missed in most biochemical assays. Fluorescent probes that non-invasively report the changing subcellular location of Rho GTPase activity in single living cells are now allowing us to examine spatio-temporal regulation of the activity of these proteins, and are providing new biological insights. Several strategies can be used to construct such probes, and there are advantages and disadvantages associated with the diverse probe designs.
Rho-family GTPases: it's not only Rac and Rho (and I like it)
Authors: Wennerberg Krister , Der Channing J.
Published: March 2004

The Rho-family proteins make up a major branch of the Ras superfamily of small GTPases. To date, 22 human genes encoding at least 25 proteins have been described. The best known `classical' members are RhoA, Rac1 and Cdc42. Highly related isoforms of these three proteins have not been studied as intensively, in part because it has been assumed that they are functionally identical to their better-studied counterparts. This now appears not to be the case. Variations in C-terminal-signaled modifications and subcellular targeting cause otherwise highly biochemically related isoforms (e.g. RhoA, RhoB and RhoC) to exhibit surprisingly divergent biological activities. Whereas the classical Rho GTPases are regulated by GDP/GTP cycling, other Rho GTPases are also regulated by other mechanisms, particularly by transcriptional regulation. Newer members of the family possess additional sequence elements beyond the GTPase domain, which suggests they exhibit yet other mechanisms of regulation.
Watch thy neighbor: cancer is a communal affair
Authors: Weaver Valerie M. , Gilbert Penney
Published: March 2004

Malignant transformation of an epithelium occurs within the context of a dynamically evolving tissue stroma that is composed of multiple cell types surrounded by an extracellular matrix. Because stromal-epithelial interactions regulate tissue homeostasis and can profoundly influence tumorigenesis it has been proposed that the stromal microenvironment is an epigenetic tumor modifier that can either positively or negatively regulate the malignant behavior of genetically aberrant cells. New work reported in this issue of Journal of Cell Science now provides compelling evidence that alterations in the stroma are necessary and also sufficient for induction of malignant behavior by genetically normal cells.
A Nonsense Mutation of the Sodium Channel GeneSCN2Ain a Patient with Intractable Epilepsy and Mental Decline
Authors: Kamiya Kazusaku , Kaneda Makoto , Sugawara Takashi , Mazaki Emi , Okamura Nami , Montal Mauricio , Makita Naomasa , Tanaka Masaki , Fukushima Katsuyuki , Fujiwara Tateki , Inoue Yushi , Yamakawa Kazuhiro
Published: March 2004

Mutations, exclusively missense, of voltage-gated sodium channel α subunit type 1 (SCN1A) and type 2 (SCN2A) genes were reported in patients with idiopathic epilepsy: generalized epilepsy with febrile seizures plus. Nonsense and frameshift mutations ofSCN1A, by contrast, were identified in intractable epilepsy: severe myoclonic epilepsy in infancy (SMEI). Here we describe a first nonsense mutation ofSCN2Ain a patient with intractable epilepsy and severe mental decline. The phenotype is similar to SMEI but distinct because of partial epilepsy, delayed onset (1 year 7 months), and absence of temperature sensitivity. A mutational analysis revealed that the patient had a heterozygousde novononsense mutation R102X ofSCN2A. Patch-clamp analysis of Nav1.2 wild-type channels and the R102X mutant protein coexpressed in human embryonic kidney 293 cells showed that the truncated mutant protein shifted the voltage dependence of inactivation of wild-type channels in the hyperpolarizing direction. Analysis of the subcellular localization of R102X truncated protein suggested that its dominant negative effect could arise from direct or indirect cytoskeletal interactions of the mutant protein. Haploinsufficiency of Nav1.2 protein is one plausible explanation for the pathology of this patient; however, our biophysical findings suggest that the R102X truncated protein exerts a dominant negative effect leading to the patient's intractable epilepsy.
Dopamine Release in Response to a Psychological Stress in Humans and Its Relationship to Early Life Maternal Care: A Positron Emission Tomography Study Using [11C]Raclopride
Authors: Pruessner Jens C. , Champagne Frances , Meaney Michael J. , Dagher Alain
Published: March 2004

Mesolimbic dopamine is thought to play a role in the processing of rewards. However, animal studies also demonstrate dopamine release in response to aversive stressful stimuli. Also, in animal studies, disruptions of the mother–infant relationship have been shown to have long-lasting effects on the mesolimbic dopamine system and the hypothalamic-pituitary adrenal axis. We therefore investigated dopamine release in response to stress in human subjects, considering the relationship to early life parental care. We screened 120 healthy young college students for parental care in early life using a combination of telephone interviews and questionnaires. Five students from the top end and five students from the bottom end of the parental care distribution were then invited for a positron emission tomography study using [11C]raclopride and a psychosocial stress task. The psychosocial stressor caused a significant release of dopamine in the ventral striatum as indicated by a reduction in [11C]raclopride binding potential in the stress versus resting condition in subjects reporting low parental care. Moreover, the magnitude of the salivary cortisol response to stress was significantly correlated with the reduction in [11C]raclopride binding in the ventral striatum (r= 0.78), consistent with a facilitating effect of cortisol on dopamine neuron firing. These data suggest that aversive stressful events can be associated with mesolimbic dopamine release in humans, and that the method presented here may be useful to study the effects of early life events on neurobiological stress systems.
An Arginine Involved in GABA Binding and Unbinding But Not Gating of the GABAAReceptor
Authors: Wagner David A. , Czajkowski Cynthia , Jones Mathew V.
Published: March 2004

GABAAreceptor function can be conceptually divided into interactions between ligand and receptor (binding) and the opening and closing of the ligand-bound channel (gating). The relationship between binding, gating, and receptor structure remains unclear. Studies of mutations have identified many amino acid residues that contribute to the GABAbinding site. Most of these studies assayed changes in GABA dose–response curves, which are macroscopic measures that depend on the interplay of many processes and cannot resolve individual microscopic transitions. Understanding the microscopic basis of binding and gating is critical, because kinetic transition rates predict how receptors will behave at synapses. Furthermore, microscopic rates are directly related to the molecular interactions underlying receptor function.

Here, we focused on a residue (β2-R207) previously identified as lining the GABA-binding site that, when mutated to cysteine, greatly reduces apparent GABA affinity and was predicted to affect both binding and gating. To better understand the role of β2-R207, we expressed α1β2and α1β2-R207C receptors in human embryonic kidney 293 cells and studied receptor kinetics using fast solution applications. The mutation accelerated deactivation by 10-fold, without altering desensitization in the presence of saturating GABA. Maximum open probability and single-channel open times were also unaltered by the mutation, but the GABA-binding rate was reduced eightfold. Therefore, the effects of this mutation in a predicted binding site residue are solely attributable to changes in GABA-binding and unbinding kinetics, with no changes in channel gating. Because β2-R207 stabilizes GABA in the binding pocket, it may directly contact the GABA molecule.
Presynaptic NMDA Receptors Modulate Glutamate Release from Primary Sensory Neurons in Rat Spinal Cord Dorsal Horn
Authors: Bardoni Rita , Torsney Carole , Tong Chi-Kun , Prandini Massimiliano , MacDermott Amy B.
Published: March 2004

NMDA receptors have the potential to produce complex activity-dependent regulation of transmitter release when localized presynaptically. In the somatosensory system, NMDA receptors have been immunocytochemically detected on presynaptic terminals of primary afferents, and these have been proposed to drive release of substance P from central terminals of a subset of nociceptors in the spinal cord dorsal horn. Here we report that functional NMDA receptors are indeed present at or near the central terminals of primary afferent fibers. Furthermore, we show that activation of these presynaptic receptors results in an inhibition of glutamate release from the terminals. Some of these NMDA receptors may be expressed in the preterminal axon and regulate the extent to which action potentials invade the extensive central arborizations of primary sensory neurons.
The Orexin/Hypocretin System in Zebrafish Is Connected to the Aminergic and Cholinergic Systems
Authors: Kaslin Jan , Nystedt Johanna M. , Östergård Maria , Peitsaro Nina , Panula Pertti
Published: March 2004

The orexin/hypocretin (ORX) system is involved in physiological processes such as feeding, energy metabolism, and the control of sleep and wakefulness. The ORX system may drive the aminergic and cholinergic activities that control sleep and wakefulness states because of the ORX fiber projections to the aminergic and cholinergic cell clusters. The biological mechanisms and relevance of the interactions between these neurotransmitter systems are poorly understood. We studied these systems in zebrafish, a model organism in which it is possible to simultaneously study these systems and their interactions.

We cloned a zebrafish prepro-ORX gene that encodes for the two functional neuropeptides orexin-A (ORX-A) and orexin-B (ORX-B). The prepro-ORX gene of the zebrafish consisted of one exon in contrast to mammals. The sequence of the ORX-A peptide of the zebrafish was less conserved than the ORX-B peptide compared with other vertebrates. By usingin situhybridization and immunohistochemistry, we found that the organization of the ORX system of zebrafish was similar to the ORX system in mammals, including a hypothalamic cell cluster and widespread fiber projections. The ORX system of the zebrafish showed a unique characteristic with an additional putatively ORX-containing cell group. The ORX system innervated several aminergic nuclei, raphe, locus ceruleus, the mesopontine-like area, dopaminergic clusters, and histaminergic neurons. A reciprocal relationship was found between the ORX system and several aminergic systems. Our results suggest that the architecture of these neurotransmitter systems is conserved in vertebrates and that these neurotransmitter systems in zebrafish may be involved in regulation of states of wakefulness and energy homeostasis by similar mechanisms as those in mammals.
Inhibitory Control at a Synaptic Relay
Authors: Awatramani Gautam B. , Turecek Rostislav , Trussell Laurence O.
Published: March 2004

The mammalian medial nucleus of the trapezoid body (MNTB) harbors one of the most powerful terminals in the CNS, the calyx of Held. The mechanisms known to regulate this synaptic relay are relatively ineffective. Here, we report the presence of a remarkably robust and fast-acting glycinergic inhibitory system capable of suppressing calyceal transmission.

Evoked glycinergic IPSCs were relatively small in 2-week-old rats, an age by which calyceal maturation has reportedly neared completion. However, by postnatal day 25 (P25), glycinergic transmission had undergone a vigorous transformation, resulting in peak synaptic conductances as high as 280 nS. These are comparable with glutamatergic conductances activated by calyceal inputs. Decay kinetics for IPSCs were severalfold faster than for glycinergic synaptic events reported previously. At physiological temperatures in P25 rats, IPSCs decayed in ∼1 msec and could be elicited at frequencies up to 500 Hz. Moreover, EPSPs triggered by glutamatergic signals derived from the calyx or simulated by conductance clamp were suppressed when preceded by simulated glycinergic IPSPs. The matching of excitatory transmission in the calyx of Held by a powerful, precision inhibitory system suggests that the relay function of the MNTB may be rapidly modified during sound localization.
Organic Cation Transporter 3 (Slc22a3) Is Implicated in Salt-Intake Regulation
Authors: Vialou Vincent , Amphoux Anne , Zwart Ronald , Giros Bruno , Gautron Sophie
Published: March 2004

Organic cation transporters (OCTs) are carrier-type permeases known to participate in general detoxification functions in peripheral tissues. Previousin vitrostudies have suggested that OCTs ensure Uptake2, a low-affinity, corticosteroid-sensitive catecholamine removal system, which was characterized initially in sympathetically innervated tissues. Although the presence of both Uptake2-like transport and most OCT subtypes has also been demonstrated in the brain, the physiological role of this family of transporters in CNS remained totally unknown. In the present work, we show that the OCT3 transporter is found throughout the brain and highly expressed in regions regulating fluid exchange, including circumventricular organs such as area postrema and subfornical organ (SFO), and in other structures implicated in the sensing of changes in blood osmolarity and regulation of salt and water ingestion. OCT3/Slc22a3-deficient mice show an increase in the level of ingestion of hypertonic saline under thirst and salt appetite conditions, as well as alterations of the neural response in the SFO after sodium deprivation, as monitored by Fos immunoreactivity. This work demonstrates that the presence of OCT3 is critical for the balanced neural and behavioral responses to environmentally induced variations in osmolarity and provides for the first time physiological evidence of the importance of OCTs for CNS function.
An Outer Segment Localization Signal at the C Terminus of the Photoreceptor-Specific Retinol Dehydrogenase
Authors: Luo Wenqin , Marsh-Armstrong Nicholas , Rattner Amir , Nathans Jeremy
Published: March 2004

Photoreceptor retinol dehydrogenase (prRDH) is a membrane-associated cytosolic protein that localizes to the outer segments (OS) of rods and cones. Here, we demonstrate that the C-terminal 16 amino acids of prRDH confer membrane association as well as cone and rod OS targeting on a linked green fluorescent protein. Membrane association in transfected 293 cells and in transgenicXenopusphotoreceptors is mediated by fatty acylation at one or more evolutionarily conserved cysteines within the prRDH C-terminal tail. In bovine OS, native prRDH is similarly acylated, and hydrolysis of this linkage releases the protein from the membrane. Efficient OS localization requires both membrane association and the prRDH sequence... (V/I)XPX at the extreme C terminus, which closely resembles the C-terminal sequence that targets opsin/rhodopsin to the OS. Taken together, these data imply that the C-terminal... (V/I)XPX sequence is a general OS localization signal that can function in the context of both integral and peripheral membrane proteins. This strategy for OS localization resembles those used for protein localization to mitochondria, peroxisomes, endosomes, and endoplasmic reticulum; in each case, a short N- or C-terminal sequence is shared among structurally diverse proteins that are targeted to the same subcellular destination.
Anterograde Transneuronal Viral Tracing of Central Viscerosensory Pathways in Rats
Authors: Rinaman Linda , Schwartz Gary
Published: March 2004

Previous studies demonstrated that strain H129 of herpes simplex virus-1 undergoes anterograde transneuronal transport in mice and primates after peripheral or central injection. In this study, H129 was used in rats to identify CNS regions that receive relayed viscero-sensory inputs from the stomach wall. We also examined whether transneuronal viral transport in this model is exclusively anterograde. H129 or an established retrograde transneuronal viral tracer, pseudorabies virus (PRV), was injected into the ventral stomach wall in intact rats or in rats with previous subdiaphragmatic vagal sensory deafferentation. Rats were perfused with fixative 3–5 d later, and tissues were processed for immunocytochemical detection of transported virus. In intact rats, H129 was transported transneuronally via vagal and spinal viscerosensory neurons to postsynaptic target cells in the medullary dorsal vagal complex and thoracic dorsal horn, respectively, with subsequent transport to discrete regions of the medullary and pontine reticular formation, cerebellum, parabrachial nucleus, periaqueductal gray, thalamus, hypothalamus, amygdala, bed nucleus of the stria terminalis, and other central sites. Comparison of labeling patterns in intact and vagal deafferented rats indicated that H129 also produced first-order retrograde infection of autonomic neurons that project directly to virus injection sites, similar to PRV. Unlike PRV, however, H129 was not transported transneuronally in the retrograde direction from infected neurons to central sources of presynaptic input. We conclude that transneuronal transport of H129 occurs exclusively in the anterograde direction to reveal CNS regions that receive direct and relayed viscerosensory signals.
Formation of Projection Pathways from the Arcuate Nucleus of the Hypothalamus to Hypothalamic Regions Implicated in the Neural Control of Feeding Behavior in Mice
Authors: Bouret Sebastien G. , Draper Shin J. , Simerly Richard B.
Published: March 2004

The arcuate nucleus of the hypothalamus (ARH) is a critical component of forebrain pathways that regulate a variety of neuroendocrine functions, including an important role in relaying leptin signals to other parts of the hypothalamus. However, neonatal rodents do not lose weight in response to leptin treatment in the same way as do adults, suggesting that certain aspects of leptin signaling pathways in the hypothalamus may not be mature. We tested this possibility by using DiI axonal labeling to examine the development of projections from the ARH to other parts of the hypothalamus in neonatal mice, paying particular attention to the innervation of the paraventricular nucleus (PVH), the dorsomedial nucleus (DMH), and the lateral hypothalamic area (LHA), each of which have been implicated in the regulation of feeding. The results indicate that ARH projections are quite immature at birth and appear to innervate the DMH, PVH, and LHA in succession, within distinct temporal domains. The projections from the ARH to the DMH develop rapidly and are established by the sixth postnatal day (P6), whereas those to the PVH develop significantly later, with the mature pattern of innervation first apparent between postnatal day 8 (P8)-P10. Furthermore, the ability of leptin to activate Fos in the PVH, DMH, and LHA appears to be age-dependent and correlates with the arrival of ARH projections to each nucleus. Taken together, these findings provide new insight into development of hypothalamic circuits and suggest an anatomical basis for the delayed postnatal regulation of food intake and body weight by leptin.
Mechanisms of Insulin Signal Transduction
Authors: Garvey W. Timothy
Published: March 2004

The peptide hormone insulin is secreted from pancreatic β‐cells, binds to cell surface receptors, and exerts a broad spectrum of anabolic effects in multiple tissues. In mediating its pleiotrophic actions, insulin engages multiple signal transduction, pathways that affect the expression and posttranslational modification of proteins, and regulates enzymatic pathways, subcellular protein localization, and the activation state of membrane transport systems. There are three major steps that provide for divergence of insulin signal transduction, leading to different functional effects: (i) the family of insulin receptor substrate (IRS) docking molecules, (ii) activation of phosphatidylinositide 3 (PI‐3) kinase, and (iii) activation of Akt/protein kinase B (PKB). Stimulation of the glucose transport system involves activation of two parallel pathways, the IRS/PI‐3 kinase pathway (resulting in activation of Akt/PKB and PKC‐λ/ζ) and the CAP/Cbl/TC10 pathway, that then interact with systems regulating trafficking of GLUT‐4‐containing vesicles and the cytoskeleton. Furthermore, multiple mechanisms modulate insulin signal transduction by affecting the serine/threonine phosphorylation state of tyrosine kinase substrates and phosphoinositides, and the tyrosine phosphorylation state of insulin receptors and IRS molecules. Thus, promulgation of the insulin action is most accurately viewed as a flexible pattern of network interactions involving a web of signal molecule cascades and effector systems. Complex patterns of interactions among signal and effector systems allow for greater plasticity in adaptive responses, and present an increasing number of targets for therapeutic intervention in treating human insulin resistance.
Measuring Insulin ActionIn Vivo
Authors: Bergman Richard N. , Hücking Katrin , Watanabe Richard M.
Published: March 2004

The goal to accurately measure insulin sensitivity (i.e., “insulin resistance”) in patients remains an important goal. Insulin resistance is a risk factor for a plethora of chronic diseases (diabetes cardiovascular disease, hypertension, colon cancer). To study these diseases and to intervene early in their pathogenesis requires that we quantify risk factors and insulin resistance is one important candidate.To accurately measure sensitivity it is important to use a method that observes in some fashion the metabolic effect of insulin given intravenously. Thus, the glucose clamp and the minimal model are accurate and reproducible methods. One must remain vigilant regarding limitations of these methods. However, they may be applied with confidence under a wide variety of conditions. Unfortunately it is not possible to recommend simpler (i.e. surrogate) methods that can be applied with confidence. While it might be appropriate to use fasting insulin to reflect insulin resistance in patients without any degree of β‐cell failure, it is usually not possible to determinea prioriwhether any such defect exists. Thus, one can report fasting insulin simply as aqualitative reflectionof insulin resistance. Indices, which also include glucose, appear to add little to the fasting insulin itself. If β‐cell failure progresses, the interpretation of fasting insulinper sebecomes impossible. Finally, as of this writing it is not possible to recommend insulin sensitivity measures calculated from the oral glucose tolerance test due to confounds related to differences in gastric emptying, β‐cell function, and glucose effectiveness. Clearly, studies to identify and validate simpler methods to assess insulin action accurately in the intact subject should be continued.
Insulin ActionsIn Vivo: Glucose Metabolism
Authors: Ferrannini Ele , DeFronzo Ralph A.
Published: March 2004

Catheter techniques and tracer methodology employed for the study of glucose metabolismin vivoare presented in detail in order to define concepts, qualify interpretation, and outline limitations. Origin, total‐body, and regional uptake and main intracellular routes of disposition for circulating glucose are described separately for the basal and fed state, with punctual indication of the action of insulin on these processes. The physiology of the glucose/insulin system is recapitulated into points of clinical interest.
Insulin Regulation of Ketone Body Metabolism
Authors: Ciaraldi Theodore P. , Henry Robert R.
Published: March 2004

The overarching concern in the hormonal control of ketone body metabolism is the insulin level. In circumstances where insulin levels are relatively high, such as the fed state, both substrate (free fatty acid, [FFA]) availability and FFA oxidation are suppressed, directing FFA to storage and employing glucose to meet the energy needs of the body. In situations of relative insulin deficiency, such as starvation or type I diabetes, FFA oxidation is increased, driving the production of alternative energy‐producing substrates, ketone bodies, for use by the brain, as well as peripheral tissues. Insulin influences the activity of three key processes: FFA availability (lipolysis), ketone body production (ketogenesis), and disposal in peripheral tissues. All of these processes can be altered in pathophysiologic conditions such as type 1 and type 2 diabetes, obesity, starvation, and hyperthyroidism. The key control point is carnitine palmitoyltransferase‐I (CPT‐I), which mediates the passage of long chain fatty acyl coenzyme A (FA‐CoA) esters across the outer mitochondrial membrane, prior to oxidation or ketogenesis. Insulin regulates CPT‐I both at the level of gene transcription and by influencing the affinity for allosteric modulators. Regulation of hepatic CPT‐I expression or activity holds potential significance as an approach for controlling hyperglycemia and insulin resistance.