@article{2626, abstract = {The expression pattern of metabotropic glutamate receptor Iα (mGluR1α) was immunohistochemically investigated in substantia nigra dopaminergic neurons of the macaque monkey. In normal monkeys, mGluR1α immunoreactivity was weakly observed in the dorsal tier of the substantia nigra pars compacta (SNc-d) where calbindin-D28k-containing dopaminergic neurons invulnerable to parkinsonian degeneration are specifically located. On the other hand, mGluR1α was strongly expressed in the ventral tier of the substantia nigra pars cornpacta (SNc-v). In monkeys treated with the parkinsonism-inducing drug, I-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), mGluR1α expression was decreased in dopaminergic neurons in the SNc-v that were spared its toxic action. These results suggest that mGluR1α expression may be involved at least partly in the vulnerability of dopaminergic neurons to parkinsonian insults.}, author = {Kaneda, Katsuyuki and Imanishi, Michiko and Nambu, Atsushi and Ryuichi Shigemoto and Takada, Masahiko}, journal = {Neuroreport}, number = {7}, pages = {947 -- 950}, publisher = {Lippincott, Williams & Wilkins}, title = {{Differential expression patterns of mGluR1α in monkey nigral dopamine neurons}}, doi = {10.1097/01.wnr.0000074344.81633.e4}, volume = {14}, year = {2003}, } @article{2627, abstract = {Despite its implications for higher order functions of the brain, little is currently known about the molecular basis of left-right asymmetry of the brain. Here we report that synaptic distribution of N-methyl-D-aspartate (NMDA) receptor GluRε2 (NR2B) subunits in the adult mouse hippocampus is asymmetrical between the left and right and between the apical and basal dendrites of single neurons. These asymmetrical allocations of ε2 subunits differentiate the properties of NMDA receptors and synaptic plasticity between the left and right hippocampus. These results provide a molecular basis for the structural and functional asymmetry of the mature brain.}, author = {Kawakami, Ryosuke and Shinohara, Yoshiaki and Kato, Yuichiro and Sugiyama, Hiroyuki and Ryuichi Shigemoto and Ito, Isao}, journal = {Science}, number = {5621}, pages = {990 -- 994}, publisher = {American Association for the Advancement of Science}, title = {{Asymmetrical allocation of NMDA receptor ε2 subunits in hippocampal circuitry}}, doi = {10.1126/science.1082609}, volume = {300}, year = {2003}, } @article{2628, abstract = {We aimed to estimate the number of AMPA receptors (AMPARs) bound by the quantal transmitter packet, their single-channel conductance and their density in the postsynaptic membrane at cerebellar Purkinje cell synapses. The synaptic and extrasynaptic AMPARs were examined in Purkinje cells in 2- to 4-day-old rats, when they receive synaptic inputs solely from climbing fibres (CFs). Evoked CF EPSCs and whole-cell AMPA currents displayed roughly linear current-voltage relationships, consistent with the presence of GluR2 subunits in synaptic and extrasynaptic AMPARs. The mean quantal size, estimated from the miniature EPSCs (MEPSCs), was ∼300 pS. Peak-scaled non-stationary fluctuation analysis of spontaneous EPSCs and MEPSCs gave a weighted-mean synaptic channel conductance of ∼5 pS (∼7 pS when corrected for filtering). By applying non-stationary fluctuation analysis to extrasynaptic currents activated by brief glutamate pulses (5 mM), we also obtained a small single-channel conductance estimate for extrasynaptic AMPARs (∼11 pS). This approach allowed us to obtain a maximum open probability (Po,max) value for the extrasynaptic receptors (Po,max = 0.72). Directly resolved extrasynaptic channel openings in the continued presence of glutamate exhibited clear multiple-conductance levels. The mean area of the postsynaptic density (PSD) of these synapses was 0.074 μm2, measured by reconstructing electron-microscopic (EM) serial sections. Postembedding immunogold labelling by anti-GluR2/3 antibody revealed that AMPARs are localised in PSDs. From these data and by simulating error factors, we estimate that at least 66 AMPARs are bound by a quantal transmitter packet at CF-Purkinje cell synapses, and the receptors are packed at a minimum density of ∼900 μm-2 in the postsynaptic membrane.}, author = {Momiyama, Akiko and Silver, Rachel A and Häusser, Michael A and Notomi, Takuya and Wu, Yue and Ryuichi Shigemoto and Cull-Candy, Stuart G}, journal = {Journal of Physiology}, number = {1}, pages = {75 -- 92}, publisher = {Wiley-Blackwell}, title = {{The density of AMPA receptors activated by a transmitter quantum at the climbing fibre - Purkinje cell synapse in immature rats}}, doi = {10.1113/jphysiol.2002.033472}, volume = {549}, year = {2003}, } @article{2629, abstract = {The release of neurotransmitters is modulated by presynaptic metabotropic glutamate receptors (mGluRs), which show a highly selective expression and subcellular location in glutamatergic terminals in the hippocampus. Using immunocytochemistry, we investigated whether one of the receptors, mGluR7, whose level of expression is governed by the postsynaptic target, was present in GABAergic terminals and whether such terminals targeted particular cells. A total of 165 interneuron dendritic profiles receiving 466 synapses (82% mGluR7a-positive) were analysed. The presynaptic active zones of most GAD-(77%) or GABA-positive (94%) synaptic boutons on interneurons innervated by mGluR7a-enriched glutamatergic terminals (mGluR7a-decorated) were immunopositive for mGluR7a. GABAergic terminals on pyramidal cells and most other interneurons in str. oriens were mGluR7a-immunonegative. The mGluR7a-decorated cells were mostly somatostatin- and mGluR1α-immunopositive neurons in str. oriens and the alveus. Their GABAergic input mainly originated from VIP-positive terminals, 90% of which expressed high levels of mGluR7a in the presynaptic active zone. Parvalbumin-positive synaptic terminals were rare on mGluR7a-decorated cells, but on these neurons 73% of them were mGluR7a-immunopositive. Some type II synapses innervating interneurons were immunopositive for mGluR7b, as were some type I synapses. Because not all target cells of VIP-positive neurons are known it has not been possible to determine whether mGluR7 is expressed in a target-cell-specific manner in the terminals of single GABAergic cells. The activation of mGluR7 may decrease GABA release to mGluR7-decorated cells at times of high pyramidal cell activity, which elevates extracellular glutamate levels. Alternatively, the presynaptic receptor may be activated by as yet unidentified endogenous ligands released by the GABAergic terminals or the postsynaptic dendrites.}, author = {Somogyi, Péter and Dalezios, Yannis and Luján, Rafael and Roberts, John D and Watanabe, Masahiko and Ryuichi Shigemoto}, journal = {European Journal of Neuroscience}, number = {12}, pages = {2503 -- 2520}, publisher = {Wiley-Blackwell}, title = {{High level of mGluR7 in the presynaptic active zones of select populations of GABAergic terminals innervating interneurons in the rat hippocampus}}, doi = {10.1046/j.1460-9568.2003.02697.x}, volume = {17}, year = {2003}, } @article{2630, abstract = {Taste-metabotropic glutamate receptor 4 (taste-mGluR4) and the heteromers of T1R1 and T1R3 are candidate receptors involved in the sense of umami (monosodium glutamate) taste. Although the expression of group III mGluRs (taste-mGluR4) has been demonstrated in taste tissues, no mention has been made of the expression of group I mGluRs (mGluR1 and mGluR5) in taste tissues. We examined the expression of mGluR1 and mGluR5 in rat gustatory tissues by using reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, immunohistochemistry and immunoelectron microscopy. RT-PCR assay showed that mGluR1α and mGluR1β mRNAs were expressed in circumvallate papillae, but mGluR5 mRNA was not expressed. The positive signals of mGluR1 mRNA were detected only in circumvallate taste buds by in situ hybridization analysis. In cryosections of fungiform, foliate and circumvallate papillae, the antibody against mGluRla gave intense labeling on the taste hairs in all taste pores examined. In the developing taste buds, the positive signals of mGluR1α in taste hairs gradually increased with the increase in number of taste bud cells. These results show that, in addition to taste-mGluR4 and the heteromer of T1R1 and T1R3, mGluR1α may function as a receptor for glutamate (umami) taste sensation.}, author = {Toyono, Takashi and Seta, Yuji and Kataoka, Shinji and Kawano, Shintaro and Ryuichi Shigemoto and Toyoshima, Kuniaki}, journal = {Cell and Tissue Research}, number = {1}, pages = {29 -- 35}, publisher = {Springer}, title = {{Expression of metabotropic glutamate receptor group I in rat gustatory papillae}}, doi = {10.1007/s00441-003-0740-2}, volume = {313}, year = {2003}, } @article{2631, abstract = {Cyclic ADP-ribose (cADP-ribose) is a putative second messenger or modulator. However, the role of cADP-ribose in the downstream signals of the metabotropic glutamate receptors (mGluRs) is unclear. Here, we show that glutamate stimulates ADP-ribosyl cyclase activity in rat or mouse crude membranes of retina via group III mGluRs or in superior cervical ganglion via group I mGluRs. The retina of mGluR6-deficient mice showed no increase in the ADP-ribosyl cyclase level in response to glutamate. GTP enhanced the initial rate of basal and glutamate-stimulated cyclase activity. GTP-γ-S also stimulated basal activity. To determine whether the coupling mode of mGluRs to ADP-ribosyl cyclase is a feature common to individual cloned mGluRs, we expressed each mGluR subtype in NG108-15 neuroblastoma x glioma hybrid cells. The glutamate-induced stimulation of the cyclase occurs preferentially in NG108-15 cells over-expressing mGluRs1, 3, 5, and 6. Cells expressing mGluR2 or mGluRs4 and 7 exhibit inhibition or no coupling, respectively. Glutamate-induced activation or inhibition of the cyclase activity was eliminated after pre-treatment with cholera or pertussis toxin, respectively. Thus, the subtype-specific coupling of mGluRs to ADP-ribosyl cyclase via G proteins suggests that some glutamate-evoked neuronal functions are mediated by cADP-ribose.}, author = {Higashida, Haruhiro and Zhang, Jia-Sheng and Mochida, Sumiko and Chen, Xiao-Liang and Shin, Yeonsook and Noda, Mami and Hossain, Kazi Z and Hoshi, Naoto and Hashii, Minako and Ryuichi Shigemoto and Nakanishi, Shigetada and Fukuda, Yutaka and Yokoyama, Shigeru}, journal = {Journal of Neurochemistry}, number = {5}, pages = {1148 -- 1158}, publisher = {Wiley-Blackwell}, title = {{Subtype-specific coupling with ADP-ribosyl cyclase of metabotropic glutamate receptors in retina, cervical superior ganglion and NG108-15 cells}}, doi = {10.1046/j.1471-4159.2003.01751.x}, volume = {85}, year = {2003}, } @article{2632, abstract = {In many brain regions, hyperpolarization-activated cationic currents (Ih) are involved in the generation of rhythmic activities, but the role of Ih in olfactory oscillations remains unclear. Knowledge of the cellular and subcellular distributions of hyperpolarization-activated and cyclic nucleotide-gated channel (HCN) subunits is necessary for understanding the role of Ih in olfactory network activities. Using light microscopic immunocytochemistry, we demonstrate strong HCN1 labelling of the glomerular layer and moderate staining of granule cell, internal and external plexiform layers of the rat main olfactory bulb. In the glomerular layer, among many unlabelled neurons, two distinct subpopulations of juxtaglomerular cells are labelled. Approximately 10% of the juxtaglomerular cells strongly express HCN1. These small diameter cells are immunoreactive for GABA and comprise a subpopulation of periglomerular cells. An additional subset of juxtaglomerular cells (≈ 1%) expresses low levels of HCN1. They are large in diameter, GABA immunonegative but immunopositive for vesicular glutamate transporter 2, characterizing them as external tufted cells. Quantitative immunogold localization revealed that the somatic plasma membranes of periglomerular cells contain approximately four times more HCN1 labelling than those of external tufted cells. Unlike in cortical pyramidal cells, immunogold density for HCN1 does not significantly differ in somatic and dendritic plasma membranes of external tufted cells, indicating that post-synaptic potentials arriving at proximal and distal dendrites are modulated by the same density of I h. Our results demonstrate a cell type-dependent expression of HCN1 in the olfactory bulb and predict a differential contribution of distinct juxtaglomerular cell types to network oscillations.}, author = {Holderith, Noémi B and Ryuichi Shigemoto and Nusser, Zoltán}, journal = {European Journal of Neuroscience}, number = {2}, pages = {344 -- 354}, publisher = {Wiley-Blackwell}, title = {{Cell type-dependent expression of HCN1 in the main olfactory bulb}}, doi = {10.1046/j.1460-9568.2003.02756.x}, volume = {18}, year = {2003}, } @article{2633, abstract = {The modulation of calcium channels by metabotropic glutamate receptors (mGluRs) is a key event in the fine-tuning of neurotransmitter release. Here we report that, in cerebrocortical nerve terminals of adult rats, the inhibition of glutamate release is mediated by mGluR7. In this preparation, the major component of glutamate release is supported by P/Q-type Ca2+ channels (72.7%). However, mGluR7 selectively reduced the release component that is associated with N-type Ca2+ channels (29.9%). Inhibition of P/Q channels by mGluR7 is not masked by the higher efficiency of these channels in driving glutamate release when compared with N-type channels. Thus, activation of mGluR7 failed to reduce the release associated with P/Q channels when the extracellular calcium concentration, ([Ca2+]o), was reduced from 1.3 to 0.5 mM. Through Ca2+ imaging, we show that Ca2+ channels are distributed in a heterogeneous manner in individual nerve terminals. Indeed, in this preparation, nerve terminals were observed that contain N-type (31.1%; conotoxin GVIA-sensitive) or P/Q-type (64.3%; agatoxin IVA-sensitive) channels or that were insensitive to these two toxins (4.6%). Interestingly, the great majority of the responses to L-AP4 (95.4%) were observed in nerve terminals containing N-type channels. This specific co-localization of mGluR7 and N-type Ca2+-channels could explain the failure of the receptor to inhibit the P/Q channel-associated release component and also reveal the existence of specific targeting mechanisms to localize the two proteins in the same nerve terminal subset.}, author = {Millán, Carmelo and Castro, Enrique G and Torres, Magdalena and Ryuichi Shigemoto and Sánchez-Prieto, José}, journal = {Journal of Biological Chemistry}, number = {26}, pages = {23955 -- 23962}, publisher = {American Society for Biochemistry and Molecular Biology}, title = {{Co-expression of metabotropic glutamate receptor 7 and N-type Ca2+ channels in single cerebrocortical nerve terminals of adult rats}}, doi = {10.1074/jbc.M211471200}, volume = {278}, year = {2003}, } @article{2634, abstract = {To better understand the role of neurotransmitter receptors in neuronal differentiation and maturation a detailed knowledge of their identity, location and function in the plasma membrane of specific neuronal populations during development is required. Combining pre-embedding immunocytochemistry with cell tracking in embryonic brain slice cultures we show that virtually all neurons (∼98%) migrating through the lower intermediate zone (LIZ) on their way from the medial ganglionic eminence to the cerebral cortex, express GABA BR1. Blockade of GABABRs with a specific antagonist, CGP52432, resulted in a concentration-dependent accumulation of these tangentially migrating neurons in the ventricular/subventricular zones (VZ/SVZ) of the cortex and fewer cells were observed in the cortical plate/marginal zone (CP/MZ) and LIZ. Moreover, they had significantly shorter leading processes compared with similar migrating cells in control slices. Electrophysiological recording in LIZ and CP cells revealed no direct effect of either CGP52432 or the GABABR agonist, baclofen, on resting membrane properties suggesting that the effect of CGP52432 on migration might be mediated through a metabotropic action or the regulation of release of factors controlling migration. These results suggest that GABABRs have an important modulatory role in the migration of cortical interneurons.}, author = {López-Bendito, Guillermina and Luján, Rafael and Ryuichi Shigemoto and Ganter, Paul and Paulsen, Ole and Molnár, Zoltán}, journal = {Cerebral Cortex}, number = {9}, pages = {932 -- 942}, publisher = {Oxford University Press}, title = {{Blockade of GABAB receptors alters the tangential migration of cortical neurons}}, doi = {10.1093/cercor/13.9.932}, volume = {13}, year = {2003}, } @article{2635, abstract = {Metabotropic GABAB receptors mediate slow inhibitory effects presynaptically and postsynaptically. Using preembedding immunohistochemical methods combined with quantitative analysis of GABAB receptor subunit immunoreactivity, this study provides a detailed description of the cellular and subcellular localization of GABAB1a/b and GABA B2 in the rat hippocampus. At the light microscopic level, an overlapping distribution of GABAB1a/b and GABAB2 was revealed in the dendritic layers of the hippocampus. In addition, expression of the GABAB1a/b subunit was found in somata of CA1 pyramidal cells and of a subset of GABAergic interneurons. At the electron microscopic level, immunoreactivity for both subunits was observed on presynaptic and, more abundantly, on postsynaptic elements. Presynaptically, subunits were mainly detected in the extrasynaptic membrane and occasionally over the presynaptic membrane specialization of putative glutamatergic and, to a lesser extent, GABAergic axon terminals. Postsynaptically, the majority of GABAB receptor subunits were localized to the extrasynaptic plasma membrane of spines and dendritic shafts of principal cells and shafts of interneuron dendrites. Quantitative analysis revealed enrichment of GABAB1a/b around putative glutamatergic synapses on spines and an even distribution on dendritic shafts of pyramidal cells contacted by GABAergic boutons. The association of GABAB receptors with glutamatergic synapses at both presynaptic and postsynaptic sides indicates their intimate involvement in the modulation of glutamatergic neurotransmission. The dominant extrasynaptic localization of GABAB receptor subunits suggests that their activation is dependent on spillover of GABA requiring simultaneous activity of populations of GABAergic cells as it occurs during population oscillations or epileptic seizures.}, author = {Kulik, Ákos and Vida, Imre and Luján, Rafael and Haas, Carola A and López-Bendito, Guillermina and Ryuichi Shigemoto and Frotscher, Michael}, journal = {Journal of Neuroscience}, number = {35}, pages = {11026 -- 11035}, publisher = {Society for Neuroscience}, title = {{Subcellular Localization of Metabotropic GABAB Receptor Subunits GABAB1a/b and GABAB2 in the Rat Hippocampus}}, volume = {23}, year = {2003}, } @article{2637, abstract = {While the cholinergic depletion in Alzheimer's disease (AD) has been known for some time, a definitive involvement of other neurotransmitter systems has been somewhat more elusive. Our study demonstrates a clear involvement of both glutamatergic and, to a lesser extent, GABAergic neurons in an early onset transgenic mouse model of AD-like amyloid pathology. Immunohistochemical staining and subsequent quantification has revealed a statistically significant increased density of glutamatergic and GABAergic presynaptic boutons in both the plaque free and plaque adjacent cortical neuropile areas of transgenic mice as compared to non-transgenic controls. Furthermore, amyloid plaque size was shown to have a statistically significant effect on the relative area occupied by dystrophic glutamatergic neurites in the peri-plaque neuropile. These findings support our hypothesis that the amyloid pathology progresses in a time and neurotransmitter specific manner, first in the cholinergic system which appears to be most vulnerable, followed by the glutamatergic presynaptic boutons and finally the somewhat more resilient GABAergic terminals.}, author = {Bell, Karen F and De Kort, G J and Steggerda, S and Ryuichi Shigemoto and Ribeiro-da-Silva, Alfredo and Cuello, Augusto C}, journal = {Neuroscience Letters}, number = {2}, pages = {143 -- 147}, publisher = {Elsevier}, title = {{Structural involvement of the glutamatergic presynaptic boutons in a transgenic mouse model expressing early onset amyloid pathology}}, doi = {10.1016/j.neulet.2003.09.027}, volume = {353}, year = {2003}, } @article{2784, abstract = {We report the results of an experimental study of magnetohydrodynamic damping of sidewall convection in a rectangular enclosure filled with gallium. In particular we investigate the suppression of convection when a steady magnetic field is applied separately in each of the three principal directions of the flow. The strongest damping of the steady flow is found for a vertical magnetic field, which is in agreement with theory. However, we observe that the application of a field transverse to the flow provides greater damping than a longitudinal one, which seems to contradict available theory. We provide a possible resolution of this apparent dichotomy in terms of the length scale of the experiment.}, author = {Björn Hof and Juel, Anne and Mullin, Tom P}, journal = {Journal of Fluid Mechanics}, pages = {163 -- 179}, publisher = {Cambridge University Press}, title = {{Magnetohydrodynamic damping of convective flows in molten gallium}}, doi = {10.1017/S0022112003004014}, volume = {482}, year = {2003}, } @article{2785, abstract = {Experimental evidence for the scaling of the finite amplitude of perturbation theory required to promote transition in Poiseuille flow was found. The exponent is -1 and was uncovered using considerable care in the design and execution of the experiment. Interestingly, this exponent was also found in experiments on transition in boundary layers.}, author = {Björn Hof and Juel, Anne and Mullin, Tom P}, journal = {Physical Review Letters}, number = {24}, pages = {244502/1 -- 244502/4}, publisher = {American Physical Society}, title = {{Scaling of the turbulence transition threshold in a pipe}}, doi = {10.1103/PhysRevLett.91.244502}, volume = {91}, year = {2003}, } @article{2990, abstract = {Plant growth is marked by its adaptability to continuous changes in environment. A regulated, differential distribution of auxin underlies many adaptation processes including organogenesis, meristem patterning and tropisms. In executing its multiple roles, auxin displays some characteristics of both a hormone and a morphogen. Studies on auxin transport, as well as tracing the intracellular movement of its molecular components, have suggested a possible scenario to explain how growth plasticity is conferred at the cellular and molecular level. The plant perceives stimuli and changes the subcellular position of auxin-transport components accordingly. These changes modulate auxin fluxes, and the newly established auxin distribution triggers the corresponding developmental response.}, author = {Friml, Jirí}, journal = {Current Opinion in Plant Biology}, number = {1}, pages = {7 -- 12}, publisher = {Elsevier}, title = {{Auxin transport - Shaping the plant}}, doi = {10.1016/S1369526602000031}, volume = {6}, year = {2003}, } @article{2992, abstract = {Plants have many polarized cell types, but relatively little is known about the mechanisms that establish polarity. The orc mutant was identified originally by defects in root patterning, and positional cloning revealed that the affected gene encodes STEROL METHYLTRANSFERASE1, which is required for the appropriate synthesis and composition of major membrane sterols. smt1orc mutants displayed several conspicuous cell polarity defects. Columella root cap cells revealed perturbed polar positioning of different organelles, and in the smt1orc root epidermis, polar initiation of root hairs was more randomized. Polar auxin transport and expression of the auxin reporter DR5-β-glucuronidase were aberrant in smt1orc. Patterning defects in smt1orc resembled those observed in mutants of the PIN gene family of putative auxin efflux transporters. Consistently, the membrane localization of the PIN1 and PIN3 proteins was disturbed in smt1orc, whereas polar positioning of the influx carrier AUX1 appeared normal. Our results suggest that balanced sterol composition is a major requirement for cell polarity and auxin efflux in Arabidopsis.}, author = {Willemsen, Viola and Jirí Friml and Grebe, Markus and Van Den Toorn, Albert and Palme, Klaus and Scheres, Ben}, journal = {Plant Cell}, number = {3}, pages = {612 -- 625}, publisher = {American Society of Plant Biologists}, title = {{Cell polarity and PIN protein positioning in Arabidopsis require STEROL METHYLTRANSFERASE1 function}}, doi = {10.1105/tpc.008433}, volume = {15}, year = {2003}, } @article{2993, abstract = {Plant biology is currently experiencing a growing demand for easy and reliable mRNA and protein localisation techniques. Here, we present novel whole mount in situ hybridisation and immunolocalisation protocols, suitable to localise mRNAs and proteins in Arabidopsis seedlings. We demonstrate that these methods can be used in different organs of Arabidopsis seedlings as well as in other plant species. In order to achieve better reproducibility and higher throughput, we modified these protocols for automation to be performed by a liquid handling robot. In addition, we show that other procedures such as reporter enzyme assays and tissue clearing can be similarly automated. We present examples of application of our protocols including mRNA localisation and proteins and epitope tag (co)localisations which demonstrate that these methods provide reliable and versatile tools for expression, localisation and anatomical studies in plants.}, author = {Jirí Friml and Eva Benková and Mayer, Ulrike and Palme, Klaus and Muster, Gerhard}, journal = {Plant Journal}, number = {1}, pages = {115 -- 124}, publisher = {Wiley-Blackwell}, title = {{Automated whole mount localisation techniques for plant seedlings}}, doi = {10.1046/j.1365-313X.2003.01705.x}, volume = {34}, year = {2003}, } @article{2994, abstract = {The regular arrangement of leaves around a plant's stem, called phyllotaxis, has for centuries attracted the attention of philosophers, mathematicians and natural scientists; however, to date, studies of phyllotaxis have been largely theoretical. Leaves and flowers are formed from the shoot apical meristem, triggered by the plant hormone auxin. Auxin is transported through plant tissues by specific cellular influx and efflux carrier proteins. Here we show that proteins involved in auxin transport regulate phyllotaxis. Our data indicate that auxin is transported upwards into the meristem through the epidermis and the outermost meristem cell layer. Existing leaf primordia act as sinks, redistributing auxin and creating its heterogeneous distribution in the meristem. Auxin accumulation occurs only at certain minimal distances from existing primordia, defining the position of future primordia. This model for phyllotaxis accounts for its reiterative nature, as well as its regularity and stability.}, author = {Reinhardt, Didier and Pesce, Eva-Rachele and Stieger, Pia and Mandel, Therese and Baltensperger, Kurt and Bennett, Malcolm and Traas, Jan and Jirí Friml and Kuhlemeier, Cris}, journal = {Nature}, number = {6964}, pages = {255 -- 260}, publisher = {Nature Publishing Group}, title = {{Regulation of phyllotaxis by polar auxin transport}}, doi = {10.1038/nature02081}, volume = {426}, year = {2003}, } @article{2995, abstract = {Axis formation occurs in plants, as in animals, during early embryogenesis. However, the underlying mechanism is not known. Here we show that the first manifestation of the apical-basal axis in plants, the asymmetric division of the zygote, produces a basal cell that transports and an apical cell that responds to the signalling molecule auxin. This apical-basal auxin activity gradient triggers the specification of apical embryo structures and is actively maintained by a novel component of auxin efflux, PIN7, which is located apically in the basal cell. Later, the developmentally regulated reversal of PIN7 and onset of PIN1 polar localization reorganize the auxin gradient for specification of the basal root pole. An analysis of pin quadruple mutants identifies PIN-dependent transport as an essential part of the mechanism for embryo axis formation. Our results indicate how the establishment of cell polarity, polar auxin efflux and local auxin response result in apical-basal axis formation of the embryo, and thus determine the axiality of the adult plant. }, author = {Jirí Friml and Vieten, Anne and Sauer, Michael and Weijers, Dolf and Schwarz, Heinz and Hamann, Thorsten and Offringa, Remko and Jürgens, Gerd}, journal = {Nature}, number = {6963}, pages = {147 -- 153}, publisher = {Nature Publishing Group}, title = {{Efflux dependent auxin gradients establish the apical basal axis of Arabidopsis}}, doi = {10.1038/nature02085}, volume = {426}, year = {2003}, } @article{2996, abstract = {Plants, compared to animals, exhibit an amazing adaptability and plasticity in their development. This is largely dependent on the ability of plants to form new organs, such as lateral roots, leaves, and flowers during postembryonic development. Organ primordia develop from founder cell populations into organs by coordinated cell division and differentiation. Here, we show that organ formation in Arabidopsis involves dynamic gradients of the signaling molecule auxin with maxima at the primordia tips. These gradients are mediated by cellular efflux requiring asymmetrically localized PIN proteins, which represent a functionally redundant network for auxin distribution in both aerial and underground organs. PIN1 polar localization undergoes a dynamic rearrangement, which correlates with establishment of auxin gradients and primordium development. Our results suggest that PIN-dependent, local auxin gradients represent a common module for formation of all plant organs, regardless of their mature morphology or developmental origin. }, author = {Eva Benková and Michniewicz, Marta and Sauer, Michael and Teichmann, Thomas and Seifertová, Daniela and Jürgens, Gerd and Jirí Friml}, journal = {Cell}, number = {5}, pages = {591 -- 602}, publisher = {Cell Press}, title = {{Local, efflux-dependent auxin gradients as a common module for plant organ formation}}, doi = {10.1016/S0092-8674(03)00924-3}, volume = {115}, year = {2003}, } @misc{3139, abstract = {Significant advances have been made during the past few years in our understanding of how the spinal monosynaptic reflex develops. Transcription factors in the Neurogenin, Runt, ETS, and LIM families control sequential steps of the specification of various subtypes of dorsal root ganglia sensory neurons. The initiation of muscle spindle differentiation requires neuregulin 1, derived from Ia afferent sensory neurons, and signaling through ErbB receptors in intrafusal muscle fibers. Several retrograde signals from the periphery are important for the establishment of late connectivity in the reflex circuit. Finally, neurotrophin 3 released from muscle spindles regulates the strength of sensory-motor connections within the spinal cord postnatally.}, author = {Chen, Hsiao Huei and Simon Hippenmeyer and Arber, Silvia and Frank, Eric}, booktitle = {Current Opinion in Neurobiology}, number = {1}, pages = {96 -- 102}, publisher = {Elsevier}, title = {{Development of the monosynaptic stretch reflex circuit}}, doi = {10.1016/S0959-4388(03)00006-0}, volume = {13}, year = {2003}, }