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PubMed1980

Eruption of teeth into crowded position, loss of attachment, and downgrowth of subgingival plaque.

The role of crowded teeth in the etiology of attachment loss was studied in thirty teeth extracted for orthodontic reasons from eight children 12 to 13 years of age. Following extraction, the teeth were stained in a 1 percent solution of water blue and examined under the stereomicroscope. In one third of the thirty teeth, a 0.9, 2.0, and 3.5 mm. loss of attachment was observed on surfaces adjacent to which another tooth had erupted into an extremely crowded environment. On the same surfaces, subgingival plaque had grown down to the area of the cementoenamel junction. The premature loss of attachment was assumed to be mediated by collagenase derived from the regressing dental organ or from the junctional epithelium surrounding the erupting teeth. The premature downgrowth of subgingival plaque to the area of the cementoenamel junction was facilitated by the development of an irregular contact line within the interdental papilla, rather than a contact point above the papilla.

Adolescent↗
PubMed1996

Macromolecular crowding and the mandatory condensation of DNA in bacteria.

Cellular DNA in bacteria is localized into nucleoids enclosed by cytoplasm. The forces which cause condensation of the DNA into nucleoids are poorly understood. We suggest that direct and indirect macromolecular crowding forces from the surrounding cytoplasm are critical factors for nucleoid condensation, and that within a bacterial cell these crowding forces are always present at such high levels that the DNA is maintained in a condensed state. The DNA affected includes not only the preexisting genomic DNA but also DNA that is newly introduced by viral infection, replication or other means.

Bacteria↗
PubMed1985

Vernier acuity, crowding and cortical magnification.

When a vernier target is flanked by optimally positioned lines, foveal vernier discrimination is strongly degraded (Westheimer and Hauske, 1975). We confirmed this observation (Experiment I) and have mapped out a 2 dimensional "perceptive field" for crowding in the fovea using a 2 dot target (Experiment II). Crowding was also measured in peripheral vision, using either small flanking dots as masks (Experiment III), or using repetitive vernier gratings (Experiment IV). The results showed that when scaled in proportion to recent estimates of the cortical magnification factor, vernier acuity is as good in the periphery as it is centrally. Both centrally and peripherally, there appears to be a psychophysical processing module which we term a "perceptive hypercolumn". At all eccentricities vernier thresholds were found to be approximately 1/40 of the size of a perceptive hypercolumn and were elevated if interfering contours are present in the same (or adjacent) hypercolumns.

Form Perception↗
PubMed1995

Watching molecules crowd: DNA double helices under osmotic stress.

Simultaneous measurements on the packing and energetics of high-density liquid crystalline DNA phases show that the crowding of long DNA polyelectrolytes at ever increasing concentrations is accomplished through straightening of the random coils that the double helix assumes in dilute solution. X-ray scattering by ordered phases reveals that the local straightening of the molecules is also accompanied by their progressive immobilization and confinement within the molecular 'cages' created by neighboring molecules. These effects can be clearly observed through the measured energies of DNA packing under osmotic stress and through the changes in structural and dynamic characteristics of X-ray scattering from DNA in ordered arrays at different concentrations. The character of the confinement of large DNA motions for a wide range of DNA concentrations is dominated by the soft potentials of direct interaction. We do not see the power-law variation of energy vs. volume expected from space-filling fluctuations of molecules that enjoy no interaction except the hard clash of steric repulsion. Rather, in highly concentrated DNA mesophases we see a crowding of molecules through electrostatic or hydration repulsion that confines their movements and positions. This view is based on directly measured packing energies as well as on concurrently measured structural parameters while the DNA double helices are condensed under an externally applied osmotic pressure.

DNA↗
PubMed1988

Tooth size, spacing, and crowding in relation to eruption or impaction of third molars.

A study was conducted for the purpose of comparing mesiodistal tooth diameters, sum of tooth widths, and the degree of spacing or crowding in the dentitions of two groups of young adults. The subjects in the first group had complete dentitions including third molars (M3s). In the second group, all M3s had been extracted for failure to erupt. Tooth size and consequently the sum of mesiodistal tooth widths were found to be greater in the extraction group than in the group with complete dentitions. The relationship between tooth size and M3 impaction was most pronounced in female subjects. The sum of mesiodistal tooth widths is apparently one factor of importance in the cause of M3 impaction in women. The results suggest that tooth size in girls could be used at preadolescent age as one predictive variable for third molar eruption. The sexual dimorphism demonstrated regarding the relationship between tooth size and M3 impaction implies that studies in the field of M3 development and eruption should be performed on male and female subjects separately. The dental arches in the extraction group tended to be more crowded than in the group with complete dentitions. However, the differences were small and significant only as they related to the upper arches in males.

Adult↗
PubMed2005

Confinement and crowding effects on tryptophan synthase alpha2beta2 complex.

Biological molecules experience in vivo a highly crowded environment. The investigation of the functional properties of the tryptophan synthase alpha(2)beta(2) complex either entrapped in wet nanoporous silica gels or in the presence of the crowding agents dextran 70 and ficoll 70 indicates that the rates of the conformational transitions associated to catalysis and regulation are reduced, and an open and less catalytically active conformation is stabilized.

Catalysis↗
PubMed2005

The Pyst2-L phosphatase is involved in cell-crowding.

The dual-specificity phosphatase Pyst2-L was found to be over expressed in leukocytes derived from AML and ALL patients as well as in certain other solid tumors and lymphoblastoid cell lines. Pyst2-L, binds and dephosphorylates both pERKs and pJNKs proteins, and thus, plays a role in regulating the MAP kinase signaling pathway. In the present study, a comparative genomic application was used and sequence analysis of multi-organisms databases were searched in order to identify genes homologous to Pyst2-L. The Xenopus laevis MAP kinase phosphatase X17c gene and the Yeast nitrogen starvation-induced protein phosphatase Yvh1p gene were revealed to be highly homologous with Pyst2-L. Both X17c and Yvh1p genes play a role in cell cycle regulation. A down regulated expression of the Yvh1p gene occurred in Saccharomyces cerevisiae that were synchronized to the G2-phase of the cell cycle by alpha-factor. In conformity with this result, a reduction in Pyst2-L expression levels was observed in G2-phase-synchronized Human K562 cells. Finally, we were able to show that cells in highly crowded cultures express high levels of the Pyst2-L phosphatase. These observations may indicate that low levels of the Pyst2-L phosphatase are essential for the G2-phase of the cell cycle and that this phosphatase might play a role in signaling cascades induced by cellular crowding.

Amino Acid Sequence↗
PubMed2005

Molecular crowding limits the role of fetal hemoglobin in therapy for sickle cell disease.

The dominant assumption central to most treatments for sickle cell anemia has been that replacement of sickle hemoglobin (HbS) by fetal hemoglobin (HbF) would have major clinical benefit. Using laser photolysis, we have measured polymerization kinetics including rates of homogeneous and heterogeneous nucleation on mixtures of 20% and 30% HbF with HbS. We find that the present model for polymerization, including molecular crowding, can accurately predict the rates of such mixtures, by using the single assumption that no significant amount of HbF enters the polymer. The effects of replacing HbS by HbF on the rates of polymer formation are found to be significantly lower than previous measurements appeared to indicate because the impact of the replacement is also highly dependent on the total hemoglobin concentration. This is because the molecular crowding of non-polymerizing HbF offsets substantially the effects of decreasing the concentration of HbS concentration, an effect that increases with concentration. Most strikingly, the demonstrated benefit of hydroxyurea therapy in slowing the kinetics of intracellular polymerization cannot be primarily due to enhanced HbF, but must have some other origin, which could itself represent a promising therapeutic approach.

Anemia, Sickle Cell↗
PubMed2006

Dynamics of unfolded polypeptide chains in crowded environment studied by fluorescence correlation spectroscopy.

Proteins have evolved to fold and function within a cellular environment that is characterized by high macromolecular content. The earliest step of protein folding represents intrachain contact formation of amino acid residues within an unfolded polypeptide chain. It has been proposed that macromolecular crowding can have significant effects on rates and equilibria of biomolecular processes. However, the kinetic consequences on intrachain diffusion of polypeptides have not been tested experimentally, yet. Here, we demonstrate that selective fluorescence quenching of the oxazine fluorophore MR121 by the amino acid tryptophan (Trp) in combination with fast fluorescence correlation spectroscopy (FCS) can be used to monitor end-to-end contact formation rates of unfolded polypeptide chains. MR121 and Trp were incorporated at the terminal ends of polypeptides consisting of repetitive units of glycine (G) and serine (S) residues. End-to-end contact formation and dissociation result in "off" and "on" switching of MR121 fluorescence and underlying kinetics can be revealed in FCS experiments with nanosecond time resolution. We revisit previous experimental studies concerning the dependence of end-to-end contact formation rates on polypeptide chain length, showing that kinetics can be described by Gaussian chain theory. We further investigate effects of solvent viscosity and temperature on contact formation rates demonstrating that intrachain diffusion represents a purely diffusive, entropy-controlled process. Finally, we study the influence of macromolecular crowding on polypeptide chain dynamics. The data presented demonstrate that intrachain diffusion is fast in spite of hindered diffusion caused by repulsive interactions with macromolecules. Findings can be explained by effects of excluded volume reducing chain entropy and therefore accelerating the loop search process. Our results suggest that within a cellular environment the early formation of structural elements in unfolded proteins can still proceed quite efficiently in spite of hindered diffusion caused by high macromolecular content.

Diffusion↗
PubMed2004

A role for macromolecular crowding effects in the assembly and function of compartments in the nucleus.

The mechanisms which cause macromolecules to form discrete compartments within the nucleus are not understood. Here, two ubiquitous compartments, nucleoli, and PML bodies, are shown to disassemble when K562 cell nuclei expand in medium of low monovalent cation concentration; their major proteins dispersed as seen by immunofluorescence and immunoelectron microscopy, and nucleolar transcript elongation fell by approximately 85%. These compartments reassembled and nucleolar transcription recovered in the same medium after adding inert, penetrating macromolecules (8 kDa polyethylene glycol (PEG), or 10.5 kDa dextran) to 12% w/v, showing that disassembly was not caused by the low cation concentration. These responses satisfy the criteria for crowding or volume exclusion effects which occur in concentrated mixtures of macromolecules; upon expansion the macromolecular concentration within the nucleus falls, and can be restored by PEG or dextran. These observations, together with evidence of a high concentration of macromolecules in the nucleus (in the range of 100mg/ml) which must cause strong crowding forces, suggest strongly that these forces play an essential role in driving the formation, and maintaining the function of nuclear compartments. This view is consistent with their dynamic and mobile nature and can provide interpretations of several unexplained observations in nuclear biology.

Buffers↗
PubMed2004

Social crowding sensitizes high-responding rats to psychomotor-stimulant effects of morphine.

Large individual differences have been identified toward varied addictive effects as evidenced in self-administration, place conditioning, and psychomotor stimulation paradigms, which have been primarily attributed to the role of congenital factors. However, it remains unknown whether environmental factors, like extraneous social stress events, could distinctively modulate animals with differentiated biobehavioral traits, such as rats with higher motor activity (high responder, HR) developed in a novel environment and their counterparts, LR (low responder) rats. In the present study, the influence of social crowding procedure upon morphine psychomotor effect was investigated. Moreover, the roles social stress played, respectively, on HRs and LRs were explored based on previous observation that HRs not only responded more to drugs but also to stress. Our results revealed that social crowding procedure could sensitize morphine psychomotor effect as a whole, and this effect was only evident for HR but not LR rats. The individual differences toward morphine psychomotor effects was indiscernible in rats housed in normal social conditions and only turned out to be significant under stress conditions. Given the fact that the occurrence of human addictive behavior usually happens within social environment permeated with various stress factors, the genetic and environmental elements may collaboratively contribute to the ultimate susceptibility of drug-prone individuals.

Animals↗
PubMed2004

Subliminal attentional modulation in crowding condition.

In the crowding phenomenon, recognition of a visual target is impaired by other similar visual stimuli (distracters) presented near the target. This effect may be due largely to insufficient resolution of spatial attention. We showed that attention could subliminally enhance orientation selective adaptation to illusory lines in the crowding condition where target-distractor separation is beyond the limit of spatial resolution of attention. Despite the traditionally held close link between attention and awareness, here we provided evidence for subliminal attentional modulation for orientation stimuli that could not have been consciously perceived.

Adult↗
PubMed1984

Mandibular incisor dimensions and crowding.

Previous authors have suggested that well-aligned mandibular incisors are narrower mesiodistally than incisors which crowd and that reducing mesiodistal dimensions of the mandibular incisors to fit a specific size range will prevent future malalignment. This study examined 164 cases from the records of the University of Washington Department of Orthodontics, 134 of which had been orthodontically treated and were a minimum of 10 years postretention. Measurements were made from the postretention plaster casts and from serial cephalometric head films. Statistical tests showed that there was a weak association between incisor widths or MD/FL dimensions ratio and irregular alignment over the long term. Mean dimensional differences between crowded and uncrowded incisors were small in the few pooled or segregated groups in which statistically significant differences were found. When incisor dimensions were combined with pretreatment, posttreatment, or long-term cephalometric and cast measurements, only weak and not clinically useful associations were found with long-term incisor alignment. While there was a weak tendency for narrower incisors to be associated with better alignment in some instances, narrower mesiodistal widths of mandibular incisors did not ensure long-term stability in orthodontically treated cases.

Adult↗
PubMed1995

Analyses of thermodynamic data for concentrated hemoglobin solutions using scaled particle theory: implications for a simple two-state model of water in thermodynamic analyses of crowding in vitro and in vivo.

Quantitative description of the thermodynamic consequences of macromolecular crowding (excluded volume nonideality) is an important component of analyses of the thermodynamics and kinetics of noncovalent interactions of biopolymers in vivo and in concentrated polymer solutions in vitro. By analyzing previously published thermodynamic data, we have investigated extensively the comparative applicability of two forms of scaled particle theory (SPT). In both forms, macromolecules are treated as hard spheres, but MSPT, introduced by Ross and Minton, treats the solvent as a structureless continuum, whereas bulk water molecules are included explicitly as hard spheres in BSPT, an approach developed by Berg. Here we use both MSPT and BSPT to calculate the excluded volume component of the macromolecular activity coefficient of hemoglobin (Hb) at concentrations up to 509 mg/ml by fitting osmotic pressure data for Hb and sedimentation equilibrium data for Hb and sickle-cell Hb (HbS). Both forms of SPT also are used here to analyze the effects of other globular proteins (BSA and Hb) on the solubility of HbS. In applying MSPT and BSPT to analyze macromolecular crowding, the extent of hydration delta Hb (in gH2O/gprotein) is introduced as an adjustable parameter to specify the effective (hard sphere) radius of hydrated Hb. In our nonlinear least-squares fittings based on BSPT, the hard sphere radius of bulk water molecules is either fixed at 1.375 A or floated. Although both forms of SPT yield good fittings (with different values of delta Hb) at Hb concentrations up to 350 mg/ml, only BSPT gives good fittings of all available Hb osmotic pressure data as well as of the sedimentation equilibrium and solubility data. Only BSPT predicts values for delta Hb (approximately 0.5-0.6 g/g) in the range obtained for Hb from hydrodynamic measurements (approximately 0.36-0.78 g/g). These findings indicate the applicability, at least in the context of BSPT, of a simple two-state classification of water (bulk water and water of macromolecular hydration) as a basis for interpreting excluded volume nonideality in concentrated solutions of globular proteins.

Biophysical Phenomena↗
PubMed2003

Effect of dextran on protein stability and conformation attributed to macromolecular crowding.

Thermally induced transition curves of hen egg-white lysozyme were measured in the presence of several concentrations of dextran at pH 2.0 by near-UV and far-UV CD. The transition curves were fitted to a two-state model by a non-linear, least-squares method to obtain the transition temperature (T(m)), enthalpy change (deltaH(u)(T(m))), and free energy change (deltaG(u)(T)) of the unfolding transition. An increase in T(m) and almost constant deltaH(u)(T(m)) values were observed in the presence of added dextran at concentrations exceeding ca 100 g l(-1). In addition, dextran-induced conformational changes of fully unfolded protein were investigated by CD spectroscopy. Addition of high concentrations of dextran to solutions of acid-unfolded cytochrome c at pH 2.0 results in a shift of the CD spectrum from that characteristic of the fully unfolded polypeptide to that characteristic of the more compact, salt-induced molten globule state, a result suggesting that the molten globule-like state is stabilized relative to the fully unfolded form in crowded environments. Both observations are in qualitative accord with predictions of a previously proposed model for the effect of intermolecular excluded volume (macromolecular crowding) on protein stability and conformation.

Animals↗
PubMed2002

The extent of crowding in peripheral vision does not scale with target size.

Identifying a target is more difficult when distracters are present within a zone of interaction around the target. We investigated whether the spatial extent of the zone of interaction scales with the size of the target. Our target was a letter T in one-of-four orientations. Our distracters were four squared-thetas in one-of-two orientations, presented one in each of the four cardinal directions, equidistant from the target. Target-distracter separation was varied and the proportion of correct responses at each separation was determined. From these the extent of interaction was estimated. This procedure was repeated for different target sizes spread over a 5-fold range. In each case, the contrast of the target was adjusted so that its visibility was constant across target sizes. The experiment was performed in the luminance domain (grey targets on grey background) and in the chromatic domain (green target on equiluminant grey background). In the luminance domain, target size had only a small effect on the extent of interaction; these interactions did not scale with target size. The extents of interaction for chromatic stimuli were similar to those for luminance stimuli. For a fixed target visibility, decreasing the duration of the stimulus resulted in an increase in the extent of interaction. The relevance of our findings is discussed with regard to a variety of proposed explanations for crowding. Our results are consistent with an attention-based explanation for crowding.

Attention↗
PubMed2000

The foveal 'crowding' effect: physics or physiology?

It has been known for some time that both foveal and peripheral visual acuity is higher for single letters than for letters in a row. Early work showed that this was due to the destructive interaction of adjacent contours (termed 'crowding' or contour interaction). It has been assumed to have a neural basis and a number of competing explanations have been advanced which implicate either high-level or low-level stages of visual processing. Our results suggest a much simpler explanation, one primarily determined by the physics of the stimulus rather than the physiology of the visual system. We show that, under conditions of contour interaction or 'crowding', the most relevant physical spatial frequency band of the letter is displaced to higher spatial frequencies and that foveal vision tracks this change in spatial scale.

Form Perception↗