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PubMed1998

Large-scale screening for developmental genes in embryonic stem cells and embryoid bodies using retroviral entrapment vectors.

Mammalian development is orchestrated by a variety of cellular proteins with expression that is regulated precisely. Although some of the genes encoding these factors have been identified, largely by homology to those of simpler organisms, the majority of them presumably remain unknown. We report here on the results of a large-scale genetic screen that can potentially lead to the identification of many of these unidentified genes in mice. The method we developed takes advantage of the fact that many of the factors that regulate early development are expressed at highly specific stages of early embryogenesis. We therefore established a method for tagging candidate developmental genes by virtue of their expression in a stage-specific manner during formation of embryoid bodies without a bias for their expression in undifferentiated embryonic stem (ES) cells. Of 2,400 ES cell clones with random insertions of retroviral vectors carrying a human placental alkaline phosphatase reporter gene (AP), 41 clones exhibited stage-specific reporter gene expression during embryoid body formation. The majority of these insertions were in genes that are not expressed in undifferentiated ES cells. Eleven ES cell clones with characteristic patterns of AP reporter gene expression in vitro were chosen for further examination in vivo for AP expression in developing embryos. Ten ES cell clones exhibited AP expression between day 7.5 and day 10.5 of development. Clones that showed restricted reporter gene expression in vitro also exhibited similar temporally and spatially restricted AP expression in vivo. Sequence analysis of genomic DNA flanking several vector insertions and corresponding cDNAs suggested that several of the insertions identified a previously unidentified gene. Thus, screening for reporter gene expression during embryoid body formation provides an efficient means of enriching clones that contain vector insertions into potentially novel genes that are important for regulating different stages of early postimplantation development.

Alkaline Phosphatase↗
PubMed2006

Subicular place cells generate the same "map" for different environments: comparison with hippocampal cells.

Since the initial discovery of place cells in the hippocampus proper, similar spatial firing has been observed in additional regions throughout the hippocampal formation. One such region is the subiculum. Here, most cells show a significant, consistent variation in rate relative to location. Thus, subicular and hippocampal cells are similar, in providing a representation of momentary location in space. However, there are also some fundamental differences. First, many subicular cells have a directional signal superimposed on the place-related patterns. In contrast, hippocampal cells in the open field paradigm used here typically do not show a genuine directional component. The second critical difference has to do with how the cells code different environments. As is well known, hippocampal cells show different spatial patterns in environments which offer distinctly different stimulus properties. For example, a hippocampal cell which fires in the northwest portion of a striped cylinder will likely display a different field, or no field, when recorded in a gray square. In contrast, subicular cells are likely to show the same behavior across environments, such as choosing the northwest region of both enclosures. Further, if two environments differ in size, the subicular patterns will expand/shrink to fit. Thus, it appears that subicular cells form a rigid framework of interrelated firing fields which is fit into each new enclosure. In contrast, hippocampal cells create a new "map" specific to each environment. This suggests that the hippocampal and subicular regions work together to help provide the overall cognitive mapping abilities of the animal.

Action Potentials↗
PubMed2006

Memory formation by neuronal synchronization.

Cognitive functions not only depend on the localization of neural activity, but also on the precise temporal pattern of activity in neural assemblies. Synchronization of action potential discharges provides a link between large-scale EEG recordings and cellular plasticity mechanisms. Here, we focus on the role of neuronal synchronization in different frequency domains for the subsequent stages of memory formation. Recent EEG studies suggest that synchronized neural activity in the gamma frequency range (around 30-100 Hz) plays a functional role for the formation of declarative long-term memories in humans. On the cellular level, gamma synchronization between hippocampal and parahippocampal regions may induce LTP in the CA3 region of the hippocampus. In order to encode spatial locations or sequences of multiple items and to guarantee a defined temporal order of memory processing, synchronization in the gamma frequency range has to be accompanied by a stimulus-locked phase reset of ongoing theta oscillations. Simultaneous gamma- and theta-dependent plasticity leads to complex learning rules required for realistic declarative memory formation. Subsequently, consolidation of declarative memories may occur via replay of newly acquired patterns in so-called sharp wave-ripple complexes, predominantly during slow-wave sleep. These irregular bursts induce longer lasting forms of synaptic plasticity in output regions of the hippocampus and in the neocortex. In summary, synchronization of neural assemblies in different frequency ranges induces specific forms of cellular plasticity during subsequent stages of memory formation.

Action Potentials↗
PubMed2005

Spontaneous symmetry breaking in self-organizing neural fields.

We extend the theory of self-organizing neural fields in order to analyze the joint emergence of topography and feature selectivity in primary visual cortex through spontaneous symmetry breaking. We first show how a binocular one-dimensional topographic map can undergo a pattern forming instability that breaks the underlying symmetry between left and right eyes. This leads to the spatial segregation of eye specific activity bumps consistent with the emergence of ocular dominance columns. We then show how a 2-dimensional isotropic topographic map can undergo a pattern forming instability that breaks the underlying rotation symmetry. This leads to the formation of elongated activity bumps consistent with the emergence of orientation preference columns. A particularly interesting property of the latter symmetry breaking mechanism is that the linear equations describing the growth of the orientation columns exhibits a rotational shift-twist symmetry, in which there is a coupling between orientation and topography. Such coupling has been found in experimentally generated orientation preference maps.

Algorithms↗
PubMed1994

A putative cell signal encoded by the folded gastrulation gene coordinates cell shape changes during Drosophila gastrulation.

The folded gastrulation (fog) gene is required during Drosophila gastrulation for two morphogenetic movements, formation of the ventral furrow and invagination of the posterior midgut primordium. fog coordinates cell shape changes during these invaginations by inducing apical constriction of cells in spatially and temporally defined manners. fog is expressed in the invagination primordia in a pattern that precisely precedes the pattern of constrictions. Overexpression of fog in the dorsoanterior region of the embryo induces ectopic constrictions, indicating localization of fog transcripts may define domains of cell shape changes. fog encodes a novel protein with a putative signal sequence but no potential transmembrane domains. We suggest fog functions as a secreted signal that activates the G protein alpha subunit encoded by concertina in neighboring cells. Our analyses indicate that cell-cell communication ensures the rapid, orderly progression of constriction initiations from the middle of invagination primordia out toward the margins.

Amino Acid Sequence↗
PubMed2006

Theoretical analysis of a synaptotropic dendrite growth mechanism.

It is generally believed that the genome cannot encode explicit instructions to form each synaptic connection in the nervous system, but may provide general neurite growth mechanisms which will result in proper connectivity. Recent in vivo imaging has provided evidence for a synaptotropic growth mechanism, wherein synapses could influence dendrite growth by selectively stabilizing filopodia upon which they form. We undertook a theoretical investigation into the consequences of such a growth process. Discrete stochastic simulations demonstrate that the synaptotropic mechanism can result in decreased dendritic wiring length, is capable of searching for regions of high density pre-synaptic partners, and can recapitulate specific patterns of dendrite growth and connectivity. A mean-field analysis shows that growth by selective stabilization of filopodia can be approximated as a reaction-diffusion system, with a spatially varying diffusion constant that depends on the probability of synapse formation. Thus, growth will occur faster in regions of appropriate synaptic connections, and the net growth can be shown to climb a gradient of synaptic partner density. Synaptotropic growth thus presents a mechanism for the emergent development of connectivity based on local properties of the circuit elements, rather than explicit dependence on global guidance molecules or innate predetermined branching programs.

Animals↗
PubMed1998

A study of performance on tests from the CANTAB battery sensitive to frontal lobe dysfunction in a large sample of normal volunteers: implications for theories of executive functioning and cognitive aging. Cambridge Neuropsychological Test Automated Battery.

Several tests from the CANTAB neuropsychological test battery previously shown to be sensitive to frontal lobe dysfunction were administered to a large group of normal volunteers (N = 341) ranging in age from 21 to 79 years. The main tests included a computerized form of the Tower of London test of planning, a self-ordered spatial working memory task, and a test of attentional set formation and shifting. A computerized form of the Corsi spatial span task was also given. Age-related graded declines in performance were seen, sometimes in a discontinuous manner, especially for the attentional set shifting task (at the extradimensional shift stage). Patterns of deficits reminiscent of frontal lobe or basal ganglia damage were observed in the oldest age group (74-79). However, overall the data were only partially consistent with the hypothesis that frontal lobe functions are the most sensitive to effects of aging. Factor analyses showed that performance in the executive tests was not simply related to a measure of fluid intelligence, and their performance had a factor loading structure distinct from that for the CANTAB tests of visual memory and learning previously administered to the same sample. Finally, only limited support was found for the hypothesis that cognitive aging depends on slowed information processing.

Adult↗
PubMed2007

What counts as by? Young children's use of relative distance to judge nearbyness.

The authors investigated how 3- and 4-year-old children and adults use relative distance to judge nearbyness. Participants judged whether several blocks were by a landmark. The absolute and relative distance of the blocks from the landmark varied. In Experiment 1, judgments of nearbyness decreased as the distance from the landmark increased, particularly for 4-year-olds and adults. In Experiment 2, 4-year-olds and adults were more likely to judge objects at an intermediate distance as by the landmark when intervening objects were absent than when intervening objects were present. In Experiment 3, participants of all ages were more likely to judge objects at a short distance as by the landmark when intervening objects were absent. Reliance on relative distance to judge nearbyness becomes more systematic and applicable to larger spatial extents across development.

Adult↗
PubMed2001

Same-different conceptualization by baboons (Papio papio): the role of entropy.

The authors trained 6 baboons (Papio papio) to make 1 of 2 report responses to 16-icon same arrays versus 16-icon different arrays. In the same arrays, the icons were all the same as one another, whereas in the different arrays the icons were all different from one another. In Experiment 1, the baboons discriminated the same arrays from the different arrays, and they transferred their discriminative responding to arrays of novel icons. In Experiments 2 and 3, the baboons exhibited strong sensitivity to the degree of display variability when they were shown mixed arrays that comprised some same and some different items. The information theoretic measure "entropy" systematically described these results and outperformed several rival metrics. Finally, in Experiments 4 and 5, the baboons' responses to displays that contained jittered and blurred icons suggested that their same-different conceptual behavior was not based on the spatial orderliness of the visual arrays.

Animals↗
PubMed2001

Parametrically forced pattern formation.

Pattern formation in a nonlinear damped Mathieu-type partial differential equation defined on one space variable is analyzed. A bifurcation analysis of an averaged equation is performed and compared to full numerical simulations. Parametric resonance leads to periodically varying patterns whose spatial structure is determined by amplitude and detuning of the periodic forcing. At onset, patterns appear subcritically and attractor crowding is observed for large detuning. The evolution of patterns under the increase of the forcing amplitude is studied. It is found that spatially homogeneous and temporally periodic solutions occur for all detuning at a certain amplitude of the forcing. Although the system is dissipative, spatial solitons are found representing domain walls creating a phase jump of the solutions. Qualitative comparisons with experiments in vertically vibrating granular media are made. (c) 2001 American Institute of Physics.

Journal Article↗
PubMed2006

Alterations of M-cadherin, neural cell adhesion molecule and beta-catenin expression in satellite cells during overload-induced skeletal muscle hypertrophy.

AIM: Neural cell adhesion molecule (NCAM) and M-cadherin are cell adhesion molecules expressed on the surface of skeletal muscle satellite cell (SC). During myogenic morphogenesis, M-cadherin participates in mediating terminal differentiation and fusion of myoblasts by forming a complex with beta-catenin and that NCAM contributes to myotube formation by fusion of myoblasts. Hypertrophy and hyperplasia of functionally overloaded skeletal muscle results from the fusion with SCs into the existing myofibres or new myofibre formation by SC-SC fusion. However, the alterations of NCAM, M-cadherin and beta-catenin expressions in SCs in response to functional overload have not been investigated. METHODS: Using immunohistochemical approaches, we examined the temporal and spatial expression patterns of these factors expressed in SCs during the functional overload of skeletal muscles. RESULTS: Myofibres with SCs showing NCAM+/M-cadherin-, NCAM+/M-cadherin+ or NCAM-/M-cadherin+ were detected in overloaded muscles. The percentage changes of myofibres with SCs showing NCAM+/M-cadherin-, NCAM+/M-cadherin+ or NCAM-/M-cadherin+ were elevated in day-3 post-overloaded muscles, and then only the percentage changes of myofibres with SCs showing NCAM-/M-cadherin+ were significantly increased in day-7 post-overload muscles (P < 0.05). Both beta-catenin and M-cadherin were co-localized throughout quiescent, proliferation and differentiation stages of SCs. CONCLUSION: These results suggested that the expressions of NCAM, M-cadherin and beta-catenin in SCs may be controlled by distinct regulatory mechanisms during functional overload, and that interactions among NCAM, M-cadherin and beta-catenin in SCs may play important roles to contribute to overload-induced muscle hypertrophy via fusion with each other or into the existing myofibres of SCs.

Animals↗
PubMed2005

Genetic evidence that GTP is required for transposition of IS903 and Tn552 in Escherichia coli.

Surprisingly little is known about the role of host factors in regulating transposition, despite the potentially deleterious rearrangements caused by the movement of transposons. An extensive mutant screen was therefore conducted to identify Escherichia coli host factors that regulate transposition. An E. coli mutant library was screened using a papillation assay that allows detection of IS903 transposition events by the formation of blue papillae on a colony. Several host mutants were identified that exhibited a unique papillation pattern: a predominant ring of papillae just inside the edge of the colony, implying that transposition was triggered within these cells based on their spatial location within the colony. These mutants were found to be in pur genes, whose products are involved in the purine biosynthetic pathway. The transposition ring phenotype was also observed with Tn552, but not Tn10, establishing that this was not unique to IS903 and that it was not an artifact of the assay. Further genetic analyses of purine biosynthetic mutants indicated that the ring of transposition was consistent with a GTP requirement for IS903 and Tn552 transposition. Together, our observations suggest that transposition occurs during late stages of colony growth and that transposition occurs inside the colony edge in response to both a gradient of exogenous purines across the colony and the developmental stage of the cells.

DNA Transposable Elements↗
PubMed2006

Somite formation and expression of MyoD, myogenin and myosin in Atlantic halibut (Hippoglossus hippoglossus L.) embryos incubated at different temperatures: transient asymmetric expression of MyoD.

Genes encoding the myogenic regulating factors MyoD and myogenin and the structural muscle proteins myosin light chain 2 (MyLC2) and myosin heavy chain (MyHC) were isolated from juvenile Atlantic halibut (Hippoglossus hippoglossus L.). The impact of temperature on their temporal and spatial expression during somitogenesis were examined by incubating halibut embryos at 4, 6 and 8 degrees C, and regularly sampling for whole-mount in situ hybridisation and reverse transcription (RT)-PCR. There were no significant effects of temperature on the onset of somitogenesis or number of somites at hatching. The rate of somite formation increased with increasing temperature, and the expression of MyoD, myogenin and MyHC followed the cranial-to-caudal somite formation. Hence, no significant effect of temperature on the spatial and temporal expression of the genes studied was found in relation to somite stage. MyoD, which has subsequently been shown to encode the MyoD2 isoform, displayed a novel bilaterally asymmetric expression pattern only in white muscle precursor cells during early halibut somitogenesis. The expression of myogenin resembled that previously described for other fish species, and preceded the MyHC expression by approximately five somites. Two MyLC2 cDNA sequences were for the first time described for a flatfish, probably representing embryonic (MyLC2a) and larval/juvenile (MyLC2b) isoforms. Factors regulating muscle determination, differentiation and development have so far mostly been studied in vertebrates with external bilateral symmetry. The findings of the present study suggest that more such investigations of flatfish species could provide valuable information on how muscle-regulating mechanisms work in species with different anatomical, physiological and ecological traits.

Amino Acid Sequence↗
PubMed2006

Predictability of locomotion: effects on updating of spatial situation models during narrative comprehension.

We investigated how the updating of spatial situation models during narrative comprehension depends on the interaction of cognitive abilities and text characteristics. Participants with low verbal and visuospatial abilities and participants with high abilities read narratives in which the protagonist's motions in a fictitious building were either highly predictable or very hard to predict. In Experiment 1, high-ability readers updated spatial situation models only if the protagonist's motions were hard to predict, whereas low-ability readers did so only if the motions were highly predictable. In Experiment 2, facilitated integrative spatial processing compensated for the low-ability participants' resource limitations. As a result, both ability groups updated spatial situation models with hard-to-predict protagonist motions. These results highlight the interactions of cognitive abilities and text characteristics in spatial situation model updating.

Adolescent↗
PubMed2004

Localized activity patterns in excitatory neuronal networks.

The existence of localized activity patterns, or bumps, has been investigated in a variety of spatially distributed neuronal network models that contain both excitatory and inhibitory coupling between cells. Here we show that a neuronal network with purely excitatory synaptic coupling can exhibit localized activity. Bump formation ensues from an initial transient synchrony of a localized group of cells, followed by the emergence of desynchronized activity within the group. Transient synchrony is shown to promote recruitment of cells into the bump, while desynchrony is shown to be good for curtailing recruitment and sustaining oscillations of those cells already within the bump. These arguments are based on the geometric structure of the phase space in which solutions of the model equations evolve. We explain why bump formation and bump size are very sensitive to initial conditions and changes in parameters in this type of purely excitatory network, and we examine how short-term synaptic depression influences the characteristics of bump formation.

Computer Simulation↗
PubMed2000

The origin and early evolution of tracheids in vascular plants: integration of palaeobotanical and neobotanical data.

Although there is clear evidence for the establishment of terrestrial plant life by the end of the Ordovician, the fossil record indicates that land plants remained extremely small and structurally simple until the Late Silurian. Among the events associated with this first major radiation of land plants is the evolution of tracheids, complex water-conducting cells defined by the presence of lignified secondary cell wall thickenings. Recent palaeobotanical analyses indicate that Early Devonian tracheids appear to possess secondary cell wall thickenings composed of two distinct layers: a degradation-prone layer adjacent to the primary cell wall and a degradation-resistant (possibly lignified) layer next to the cell lumen. In order to understand better the early evolution of tracheids, developmental and comparative studies of key basal (and potentially plesiomorphic) extant vascular plants have been initiated. Ultrastructural analysis and enzyme degradation studies of wall structure (to approximate diagenetic alterations of fossil tracheid structure) have been conducted on basal members of each of the two major clades of extant vascular plants: Huperzia (Lycophytina) and Equisetum (Euphyllophytina. This research demonstrates that secondary cell walls of extant basal vascular plants include a degradation-prone layer ('template layer') and a degradation-resistant layer ('resistant layer'). This pattern of secondary cell wall formation in the water-conducting cells of extant vascular plants matches the pattern of wall thickenings in the tracheids of early fossil vascular plants and provides a key evolutionary link between tracheids of living vascular plants and those of their earliest fossil ancestors. Further studies of tracheid development and structure among basal extant vascular plants will lead to a more precise reconstruction of the early evolution of water-conducting tissues in land plants, and will add to the current limited knowledge of spatial, temporal and cytochemical aspects of cell wall formation in tracheary elements of vascular plants.

Biological Evolution↗
PubMed2002

Establishment of the organizing activity of the lower endodermal half of the dorsal marginal zone is a primary and necessary event for dorsal axis formation in Cynops pyrrhogaster.

The formation of the head and trunk-tail organizers in the dorsal marginal zone (DMZ) of an amphibian embryo is thought to require spatial and temporal interactions between the Nieuwkoop center and the DMZ. Recent studies of the Xenopus embryo suggested that intra-DMZ interaction is also needed to establish the regional specificity of the DMZ. However, it is not yet clarified when and how the final pattern of the head and trunk-tail organizers is established. To analyze the intra-DMZ interactions, we injected suramin into the blastocoel of the mid-blastula of the urodele, Cynops pyrrhogaster, at 6 h prior to the onset of gastrulation. The pigmented blastopore formed normally, but the convergent extension and involution of the DMZ and dorsal axis formation of the embryo were completely inhibited. Expression of gsc, chd and Lim-1 were not maintained, but noggin was unaffected in the suramin-treated embryos. Dorsal axis formation and the expression of these genes of the suramin-treated embryos were rescued by replacing the lower endodermal half of the DMZ (LDMZ) with normal LDMZ. The present results of embryological and molecular examinations indicate that organizing activity of the early Cynops gastrula DMZ is restricted to the LDMZ, and that the organizing activity of the LDMZ is established during the late blastula stages. The results also indicate that LDMZ triggers the sequential interaction within the DMZ that establishes the final pattern of the regional specificity of the DMZ, and that the formation of the LDMZ is a primary and necessary event for dorsal axis formation.

Animals↗