Evaluation and management of patients with symptoms after anti-reflux surgery

Over the past two decades, there has been an increase in the number of anti-reflux operations being performed. This is mostly due to the use of laparoscopic techniques, the increasing prevalence of gastroesophageal reflux disease (GERD) in the population, and the increasing unwillingness of patients to take acid suppressive medications for life. Laparoscopic fundoplication is now widely available in both academic and community hospitals, has a limited length of stay and postoperative recovery time, and is associated with excellent outcomes in carefully selected patients. Although the operation has low mortality and postoperative morbidity, it is associated with late postoperative complications, such as gas bloat syndrome, dysphagia, diarrhea, and recurrent GERD symptoms. This review summarizes the diagnostic evaluation and appropriate management of such postoperative complications. If a reoperation is needed, it should be performed by experienced foregut surgeons.

Reduced expression of antimicrobial PLUNC proteins in nasal polyp tissues of patients with chronic rhinosinusitis

BACKGROUND

Chronic rhinosinusitis (CRS) is a disease characterized by inflammation of the nasal mucosa and paranasal sinuses. This inflammation may result in part from decreased epithelial barrier and innate immune responses, leading to frequent bacterial and fungal colonization. The objectives of this study were to investigate the expression of innate immune proteins of the palate lung and nasal epithelium clone (PLUNC) family in patients with CRS.

METHODS

Nasal tissue samples were collected from control subjects and CRS patients with and without nasal polyps. Expression of the members of the PLUNC family was analyzed by real-time PCR. Expression of SPLUNC1 and LPLUNC2 proteins was analyzed by ELISA, immunoblot, and immunohistochemical analysis.

RESULTS

Levels of mRNA for most of the members of the PLUNC family were profoundly reduced in nasal polyps (NPs) compared to uncinate tissue from control subjects or patients with CRS. LPLUNC2 and SPLUNC1 proteins were decreased in NPs of patients with CRS compared to uncinate tissue from control subjects. Immunohistochemical data revealed that within submucosal glands of sinonasal tissues, SPLUNC1 and LPLUNC2 were differentially expressed, in serous and mucous cells, respectively. The decrease in the expression of these molecules is probably explained by a decrease in the number of glands in NPs as revealed by correlations with levels of the glandular marker lactoferrin.

CONCLUSIONS

Decreased SPLUNC1 and LPLUNC2 in NPs reflect a profound decrease in the number of submucosal glands. Decreased glands may lead to a localized defect in the production and release of glandular innate defense molecules.

Integrated central-autonomic multifractal complexity in the heart rate variability of healthy humans

PURPOSE OF STUDY

The aim of this study was to characterize the central-autonomic interaction underlying the multifractality in heart rate variability (HRV) of healthy humans.

MATERIALS AND METHODS

Eleven young healthy subjects participated in two separate ~40 min experimental sessions, one in supine (SUP) and one in, head-up-tilt (HUT), upright (UPR) body positions. Surface scalp electroencephalography (EEG) and electrocardiogram (ECG) were collected and fractal correlation of brain and heart rate data was analyzed based on the idea of relative multifractality. The fractal correlation was further examined with the EEG, HRV spectral measures using linear regression of two variables and principal component analysis (PCA) to find clues for the physiological processing underlying the central influence in fractal HRV.

RESULTS

We report evidence of a central-autonomic fractal correlation (CAFC) where the HRV multifractal complexity varies significantly with the fractal correlation between the heart rate and brain data (P = 0.003). The linear regression shows significant correlation between CAFC measure and EEG Beta band spectral component (P = 0.01 for SUP and P = 0.002 for UPR positions). There is significant correlation between CAFC measure and HRV LF component in the SUP position (P = 0.04), whereas the correlation with the HRV HF component approaches significance (P = 0.07). The correlation between CAFC measure and HRV spectral measures in the UPR position is weak. The PCA results confirm these findings and further imply multiple physiological processes underlying CAFC, highlighting the importance of the EEG Alpha, Beta band, and the HRV LF, HF spectral measures in the supine position.

DISCUSSION AND CONCLUSION

The findings of this work can be summarized into three points: (i) Similar fractal characteristics exist in the brain and heart rate fluctuation and the change toward stronger fractal correlation implies the change toward more complex HRV multifractality. (ii) CAFC is likely contributed by multiple physiological mechanisms, with its central elements mainly derived from the EEG Alpha, Beta band dynamics. (iii) The CAFC in SUP and UPR positions is qualitatively different, with a more predominant central influence in the fractal HRV of the UPR position.

Common multifractality in the heart rate variability and brain activity of healthy humans

The influence from the central nervous system on the human multifractal heart rate variability (HRV) is examined under the autonomic nervous system perturbation induced by the head-up-tilt body maneuver. We conducted the multifractal factorization analysis to factor out the common multifractal factor in the joint fluctuation of the beat-to-beat heart rate and electroencephalography data. Evidence of a central link in the multifractal HRV was found, where the transition towards increased (decreased) HRV multifractal complexity is associated with a stronger (weaker) multifractal correlation between the central and autonomic nervous systems.

Variability trend in the scale-free fluctuation of economic and market data

Recurring trending feature of a particular duration or size can normally be observed in the scale-free fluctuation of economic and market data. While it contradicts the notion of being scale free, trends are generally believed to exist. From the explicit result of multiplicative cascade and empirical evidence, we show the presence of local cascades underlying the recurring trend and such characteristic is in fact an integral part rather than an aberration of the scale-free fluctuation.

Scaling and organization of electroencephalographic background activity and alpha rhythm in healthy young adults

The coexistence of the broad-band fluctuation and alpha rhythm of the brain dynamics is studied based on the zero-crossing property of the local electroencephalographic (EEG) recording in eyes closed and eyes open. A two-component zero-crossing scenario, consisting of a broad-band fractal and narrow-band rhythm components, is assumed. Scaling is found in the power law distribution p(tau) approximately tau(-nu) of the crossing time interval tau of the broad-band fluctuation. In alpha dominant brain state, the alpha rhythm interval L also exhibits scaling in the form of power law distribution: p(L) approximately L(phi). Our main result is the relationship nu + phi approximately 3 that characterizes the organization of these two prominent features of the brain dynamics. The possible role of self-organized criticality of punctuated equilibrium in this organization is discussed.

Hierarchical structure in healthy and diseased human heart rate variability

It is shown that the healthy and diseased human heart rate variability (HRV) possesses a hierarchical structure of the She-Leveque (SL) form. This structure, first found in measurements in turbulent fluid flows, implies further details in the HRV multifractal scaling. The potential of diagnosis is also discussed based on the characteristics derived from the SL hierarchy.

Robustness and perturbation in the modeled cascade heart rate variability

In this study, numerical experiments are conducted to examine the robustness of using cascade to describe the multifractal heart rate variability (HRV) by perturbing the hierarchical time scale structure and the multiplicative rule of the cascade. It is shown that a rigid structure of the multiple time scales is not essential for the multifractal scaling in healthy HRV. So long as there exists a tree structure for the multiplication to take place, a multifractal HRV and related properties can be captured by using the cascade. But the perturbation of the multiplicative rule can lead to a qualitative change. In particular, a multifractal to monofractal HRV transition can result after the product law is perturbed to an additive one at the fast time scale. We suggest that this explains the similar HRV scaling transition in the parasympathetic nervous system blockade.

Acute thoracolumbar burst fractures: a new view of loading mechanisms

STUDY DESIGN

An in vitro investigation of loading mechanisms in acute thoracolumbar burst fractures.

OBJECTIVES

To assess the validity of the authors' hypothesis that anterior shear forces transmitted by the facet joints are responsible for causing the severe canal compromise associated with acute thoracolumbar burst fractures.

SUMMARY OF BACKGROUND DATA

Thoracolumbar burst fractures created in the laboratory rarely match the severity of clinical cases. To date, no studies have examined in great detail the role of facet joint loading in the burst-fracture mechanism. An incomplete understanding of loading mechanisms may contribute to the controversies regarding management.

METHODS

Nine human cadaveric motion segments were instrumented with strain gages and subjected to axial compression or axial impact coupled with an extension moment. Failure loads, strain information, and radiographs were collected.

RESULTS

Fracture patterns characteristic of acute thoracolumbar burst fractures were observed in the three specimens tested with an extension moment. In this group, high strains were also recorded at the bases of the pedicles, indicating a probable site of fracture initiation. Specimens tested in a neutral orientation experienced crush fractures without an increase in interpedicular distance. Strain patterns were more uniform in this group.

CONCLUSIONS

The severity and clinical relevance of the injuries sustained by the specimens tested in extension suggest that facet joint loading plays a critical role in the acute thoracolumbar burst-fracture loading mechanism. Fracture patterns and strain concentrations are in agreement with clinical observations as well as past experimental studies.

Simulate heart rate variability in different physiological conditions

Heart rate variability is assumed to result from a multiplicative or cascade mechanism based on its multifractal property. Numerical results on the perturbation of the cascade are given to compare HRV under parasympathetic (PNS) and sympathetic (SNS) autonomic blockades. It was found that qualitative change of the HRV multifractal, which was observed in PNS blockade, is due to the change from a multiplicative to an additive mechanism.

An integrated circuit implementation of the Huxley sarcomere model

We have developed an integrated circuit to simulate the mechanical behavior demonstrated by sarcomeres found in skeletal muscle. The circuit is based upon the mathematical description of the attachment and detachment dynamics of crossbridge populations and the force generated by the crossbridges, originally formulated by A. F. Huxley. We describe the process of designing the circuit model from the mathematical model, present the sarcomere circuit implementation, and demonstrate the transient and steady-state behaviors that the fabricated circuit produces. Comparison of our results to published mechanical behavior of skeletal muscle shows qualitative similarities. We conclude that the circuit muscle model exhibits the potential for real-time simulation of muscle contractions and could be used to give engineered systems muscle-like properties.

Cytomegalovirus ventriculoencephalitis in a bone marrow transplant recipient receiving antiviral maintenance: clinical and molecular evidence of drug resistance

We describe a case of CMV ventriculoencephalitis in a severely immunocompromised bone marrow transplant recipient who was receiving combination therapy with ganciclovir and foscarnet for treatment of viremia and retinitis. Analysis of sequential viral isolates recovered from the patient's cerebrospinal fluid suggested that disease developed because of the presence of viral resistance and, possibly, low tissue penetration of antiviral agents.

Human renal organic anion transporter 1 (hOAT1) and its role in the nephrotoxicity of antiviral nucleotide analogs

hOAT1 is a renal membrane protein able to efficiently transport acyclic nucleoside phosphonates (ANPs). When expressed in CHO cells, hOAT1 mediates the uptake and cytotoxicity of ANPs suggesting that it plays an active role in the nephrotoxicity associated with cidofovir CMV therapy and high-dose adefovir HIV therapy. Although efficiently transported by hOAT1, tenofovir did not show any significant cytotoxicity in isolated human proximal tubular cells, which correlates with the lack of nephrotoxicity observed in HIV-infected patients on prolonged tenofovir therapy.

Damping actions of the neuromuscular system with inertial loads: human flexor pollicis longus muscle

Our previous work in an animal model showed that neuromuscular damping properties help maintain limb posture by effectively dissipating mechanical energy arising from disturbances. The purpose of this study was to determine whether similar damping properties were expressed in intact, normal human muscles. To review briefly, when the reflexively active soleus muscle in a decerebrate cat is coupled to an inertial load, application of a force impulse to the load results in lightly damped oscillations. By calculating the logarithmic decrement in muscle velocity following the impulse (the decrement being related to the amount of energy dissipated from the inertia), we found that damping increased with oscillation amplitude, a nonlinear property. This nonlinearity represents an automatic compensation for larger perturbations. Our findings in parallel experiments on the interphalangeal joint of the human thumb were that the long thumb flexor, the flexor pollicis longus (FPL), displayed mechanical and reflex behavior closely comparable to that reported earlier for the cat soleus, despite differences in architectural and metabolic properties between these muscles. Specifically, by selecting experimental trials that did not include voluntary interventions, we observed amplitude-dependent differences in damping in which larger amplitude movements elicited larger damping than did smaller movements. In addition, even after accounting for amplitude-dependent differences in damping, damping was found to be larger in later cycles than in the first cycle. This nonlinearity indicates that both mechanical properties of muscle and reflex mechanisms are dependent on prior movement history. We propose that this history-dependent behavior arises from the effects of prior movement on stretch reflex gain, and these effects are mediated primarily via changes in muscle spindle properties. Recordings of electromyographic activity from the FPL, during the first and second cycles of oscillation supported this postulate of a reduced reflex gain following prior motion. The functional significance of these nonlinear damping properties is that during the initial muscle stretch, the stiffness is high, which helps to preserve the initial position (although at the expense of promoting oscillation). Subsequently, the ensuing increase in damping helps suppress continuing oscillation. This sequence of varying mechanical properties is broadly analogous to the features of a predictive, or feed-forward controller, designed to produce a response that initially maintains position, and subsequently dampens oscillations. These results show that the intrinsic properties of muscle and spinal reflexes automatically provide a complex time-varying response, appropriate for maintenance of stable limb posture.

Modeling heart rate variability in healthy humans: a turbulence analogy

Many complex systems share similar statistical characteristics. In this Letter, a turbulence analogy is proposed for the long-term heart rate variability of healthy humans. Based on such an analogy, the equivalence of an inertial range is found and a cascade model, which captures the statistical properties of the heart rate data, is given.

Tensin can induce JNK and p38 activation

Cells organize diverse types of specialized adhesion sites upon attachment to extracellular matrix (ECM) components. One of the physiological roles of such cell-ECM interactions is to initiate and regulate adhesion-mediated signal transduction responses. The association of cells with fibronectin fibrils has been shown to regulate the JNK and p38 signaling pathways. We tested whether tensin, a cytoskeletal component localized to both focal contacts and fibronectin-associated fibrillar adhesions, can induce these signaling pathways. We found that tensin overexpression resulted in activation of both the c-Jun amino-terminal kinase (JNK) and p38 pathways. Tensin-mediated JNK activation was independent of the activities of the small GTP binding proteins Rac and Cdc42, but did depend on SEK, a kinase involved in the JNK pathway. We suggest that tensin may directly activate the JNK and p38 pathways, acting downstream or independent of the activities of the small GTP binding proteins Rac and Cdc42.

Dynamics and segregation of cell-matrix adhesions in cultured fibroblasts

Here we use time-lapse microscopy to analyse cell-matrix adhesions in cells expressing one of two different cytoskeletal proteins, paxillin or tensin, tagged with green fluorescent protein (GFP). Use of GFP-paxillin to analyse focal contacts and GFP-tensin to study fibrillar adhesions reveals that both types of major adhesion are highly dynamic. Small focal contacts often translocate, by extending centripetally and contracting peripherally, at a mean rate of 19 micrometers per hour. Fibrillar adhesions arise from the medial ends of stationary focal contacts, contain alpha5beta1 integrin and tensin but not other focal-contact components, and associate with fibronectin fibrils. Fibrillar adhesions translocate centripetally at a mean rate of 18 micrometers per hour in an actomyosin-dependent manner. We propose a dynamic model for the regulation of cell-matrix adhesions and for transitions between focal contacts and fibrillar adhesions, with the ability of the matrix to deform functioning as a mechanical switch.

Damping actions of the neuromuscular system with inertial loads: soleus muscle of the decerebrate cat

A transient perturbation applied to a limb held in a given posture can induce oscillations. To restore the initial posture, the neuromuscular system must provide damping, which is the dissipation of the mechanical energy imparted by such a perturbation. Despite their importance, damping properties of the neuromuscular system have been poorly characterized. Accordingly, this paper describes the damping characteristics of the neuromuscular system interacting with inertial loads. To quantitatively examine damping, we coupled simulated inertial loads to surgically isolated, reflexively active soleus muscles in decerebrate cats. A simulated force impulse was applied to the load, causing a muscle stretch, which elicited a reflex response. The resulting deviation from the initial position gave rise to oscillations, which decayed progressively. Damping provided by the neuromuscular system was then calculated from the load kinetics. To help interpret our experimental results, we compared our kinetic measurements with those of an analogous linear viscoelastic system and found that the experimental damping properties differed in two respects. First, the amount of damping was greater for large oscillation amplitudes than for small (damping is independent of amplitude in a linear system). Second, plots of force against length during the induced movements showed that damping was greater for shortening than lengthening movements, reflecting greater effective viscosity during shortening. This again is different from the behavior of a linear system, in which damping effects would be symmetrical. This asymmetric and nonlinear damping behavior appears to be related to both the intrinsic nonlinear mechanical properties of the soleus muscle and to stretch reflex properties. The muscle nonlinearities include a change in muscle force-generating capacity induced by forced lengthening, akin to muscle yield, and the nonlinear force-velocity property of muscle, which is different for lengthening versus shortening. Stretch reflex responses are also known to be asymmetric and amplitude dependent. The finding that damping is greater for larger amplitude motion represents a form of automatic gain adjustment to a larger perturbation. In contrast, because of reduced damping at small amplitudes, smaller oscillations would tend to persist, perhaps contributing to normal or "physiological" tremor. This lack of damping for small amplitudes may represent an acceptable compromise for postural regulation in that there is substantial damping for larger movements, where energy dissipation is more critical. Finally, the directional asymmetry in energy dissipation provided by muscle and reflex properties must be reflected in the neural mechanisms for a stable posture.

Control of development by altered localization of a transcription factor in B. subtilis

In B. subtilis, the chromosome partitioning proteins Soj (ParA) and Spo0J (ParB) regulate the initiation of sporulation. Soj is a negative regulator of sporulation gene expression, and Spo0J antagonizes Soj function. Using fusions of Soj to green fluorescent protein, we found that Soj localized near the cell poles and upon entry into stationary phase oscillated from pole to pole. In the absence of Spo0J, Soj was associated predominantly with DNA. By in vivo cross-linking and immunoprecipitation, we found that Soj physically associates with developmentally regulated promoters, and this association increased in the absence of Spo0J. These results show that Soj switches localization and function depending on the chromosome partitioning protein Spo0J. We further show that mutations in the Soj ATPase domain disrupt localization and function and render Soj insensitive to regulation by Spo0J.

Determination of baroreflex gain using auto-regressive moving-average analysis during spontaneous breathing

The heart rate component of the arterial baroreflex gain (BRG) was determined with auto-regressive moving-average (ARMA) analysis during each of spontaneous (SB) and random breathing (RB) protocols. Ten healthy subjects completed each breathing pattern on two different days in each of two different body positions, supine (SUP) and head-up tilt (HUT). The R-R interval, systolic arterial pressure (SAP) and instantaneous lung volume were recorded continuously. BRG was estimated from the ARMA impulse response relationship of R-R interval to SAP and from the spontaneous sequence method. The results indicated that both the ARMA and spontaneous sequence methods were reproducible (r = 0.76 and r = 0.85, respectively). As expected, BRG was significantly less in the HUT compared to SUP position for both ARMA (mean +/- SEM; 3.5 +/- 0.3 versus 11.2 +/- 1.4 ms mmHg-1; P < 0.01) and spontaneous sequence analysis (10.3 +/- 0.8 versus 31.5 +/- 2.3 ms mmHg-1; P < 0.001). However, no significant difference was found between BRG during RB and SB protocols for either ARMA (7.9 +/- 1.4 versus 6.7 +/- 0.8 ms mmHg-1; P = 0.27) or spontaneous sequence methods (21.8 +/- 2.7 versus 20.0 +/- 2.1 ms mmHg-1; P = 0.24). BRG was correlated during RB and SB protocols (r = 0.80; P < 0.0001). ARMA and spontaneous BRG estimates were correlated (r = 0.79; P < 0.0001), with spontaneous sequence values being consistently larger (P < 0.0001). In conclusion, we have shown that ARMA-derived BRG values are reproducible and that they can be determined during SB conditions, making the ARMA method appropriate for use in a wider range of patients.

The antiviral nucleotide analogs cidofovir and adefovir are novel substrates for human and rat renal organic anion transporter 1

Nephrotoxicity is the dose-limiting clinical adverse effect of cidofovir and adefovir, two potent antiviral therapeutics. Because renal uptake likely plays a role in the etiology of cidofovir- and adefovir-associated nephrotoxicity, we attempted to identify a renal transporter capable of interacting with these therapeutics. A cDNA clone was isolated from a human renal library and designated human organic anion transporter 1 (hOAT1). Northern analysis detected a specific 2.5-kilobase pair hOAT1 transcript only in human kidney. However, reverse transcription-polymerase chain reaction revealed hOAT1 expression in human brain and skeletal muscle, as well. Immunoblot analysis of human kidney cortex demonstrated that hOAT1 is an 80- to 90-kilodalton heterogeneous protein modified by abundant N-glycosylation. Xenopus laevis oocytes expressing hOAT1 supported probenecid-sensitive uptake of [(3)H]p-aminohippurate (K(m) = 4 microM), which was trans-stimulated in oocytes preloaded with glutarate. Importantly, both hOAT1 and rat renal organic anion transporter 1 (rROAT1) mediated saturable, probenecid-sensitive uptake of cidofovir, adefovir, and other nucleoside phosphonate antivirals. The affinity of hOAT1 toward cidofovir and adefovir (K(m) = 46 and 30 microM, respectively) was 5- to 9-fold higher compared with rROAT1 (K(m) = 238 and 270 microM, respectively). These data indicate that hOAT1 may significantly contribute to the accumulation of cidofovir and adefovir in renal proximal tubules and, thus, play an active role in the mechanism of nephrotoxicity associated with these antiviral therapeutics.

Damping in reflexively active and areflexive lengthening muscle evaluated with inertial loads

Damping in reflexively active and areflexive lengthening muscle evaluated with inertial loads. J. Neurophysiol. 80: 3369-3372, 1998. Studies of active areflexive muscle have shown that during a constant velocity stretch the increment in force elicited by an incremental length change falls dramatically after a few hundred micrometers of stretch, a finding labeled as "muscle yield." The mechanical behavior after the yield was like a viscous damper, in that force varied only with velocity. In light of these observations, our aims were to determine whether viscous properties are also evident under more physiological conditions, specifically under inertial loading, and to evaluate the damping action of reflexively intact compared with that of deafferented muscle. The active soleus muscle in a decerebrate cat was forcibly stretched by a simulated inertia with a specified initial velocity. We compared muscle length changes when afferent pathways were intact with those recorded after cutting the dorsal roots. Our findings were that areflexive muscle showed highly damped responses, with large changes in mean muscle length, indicative of high viscosity relative to stiffness. In contrast, reflexively active muscle produced lightly damped oscillations, with minimal changes in mean length, reflecting low viscosity and high stiffness. It appears that the stretch reflect modifies the relative contributions of elastic and viscous-like forces, maintaining elasticity, which in turn sustains oscillations. These differences highlight tradeoffs between positional and velocity regulation, in that elastic properties of reflexively active muscle promote oscillations with modest change in mean muscle length, whereas viscous-like properties of areflexive muscle produce damped responses, with poor positional regulation.

Chromosome arrangement within a bacterium

BACKGROUND

The contour length of the circular chromosome of bacteria is greater than a millimeter but must be accommodated within a cell that is only a few micrometers in length. Bacteria do not have nucleosomes and little is known about the arrangement of the chromosome inside a prokaryotic cell.

RESULTS

We have investigated the arrangement of chromosomal DNA within the bacterium Bacillus subtilis by using fluorescence microscopy to visualize two sites on the chromosome simultaneously in the same cell. Indirect immunofluorescence with antibodies against the chromosome partition protein Spo0J were used to visualize the replication origin region of the chromosome. Green fluorescent protein fused to the lactose operon repressor Lacl was used to decorate tandem copies of the lactose operon operator lacO. A cassette of tandem operators was separately inserted into the chromosome near the origin (359 degrees), near the replication terminus (181 degrees), or at two points in between (90 degrees and 270 degrees). The results show that the layout of the chromosome is dynamic but is principally arranged with the origin and terminus maximally apart and the quarter points of the chromosome in between.

CONCLUSIONS

The use of cytological methods to visualize two chromosomal sites in the same cell has provided a glimpse of the arrangement of a bacterial chromosome. We conclude that, to a first approximation, the folding of the bacterial chromosome is consistent with, and may preserve, the linear order of genes on the DNA.

Characterization of a prokaryotic SMC protein involved in chromosome partitioning

smc of Bacillus subtilis encodes a homolog of eukaryotic SMC proteins involved in chromosome condensation, pairing, and partitioning. A null mutation in B. subtilis smc caused a temperature-sensitive-lethal phenotype in rich medium. Under permissive conditions, the mutant had abnormal nucleoids, approximately 10% of the cells were anucleate, and assembly of foci of the chromosome partitioning protein Spo0J was altered. In combination with a null mutation in spo0J, the smc mutation caused a synthetic phenotype; cell growth was slower and approximately 25% of the cells were anucleate. Our results demonstrate that the B. subtilis Smc protein, like its eukaryotic counterpart, plays an important role in chromosome structure and partitioning.

Identification and characterization of a bacterial chromosome partitioning site

We have identified a DNA site involved in chromosome partitioning in B. subtilis. This site was identified in vivo as the binding site for the chromosome partitioning protein Spo0J, a member of the ParB family of partitioning proteins. Spo0J is a site-specific DNA-binding protein that recognizes a 16 bp sequence found in spo0J. Allowing two mismatches, this sequence occurs ten times in the entire B. subtilis chromosome, all in the origin-proximal approximately 20%. Eight of the ten sequences are bound to Spo0J in vivo. The presence of a site on an otherwise unstable plasmid stabilized the plasmid in a Spo0J-dependent manner, demonstrating that this site, called parS, can function as a partitioning site. This site and Spo0J are conserved in a wide range of bacterial species.

Bipolar localization of a chromosome partition protein in Bacillus subtilis

We have determined the subcellular localization of the chromosome partition protein Spo0J of Bacillus subtilis by immunofluorescence microscopy and visualizing fluorescence of a Spo0J-GFP fusion protein. Spo0J was associated with a region of the nucleoid proximal to the cell pole, both in growing cells dividing symmetrically and in sporulating cells dividing asymmetrically. Additional experiments indicated that Spo0J was bound to sites in the origin-proximal third of the chromosome. These results show that the replicating chromosomes are oriented in a specific manner during the division cycle, with the Spo0J binding region positioned toward the cell poles. Experiments characterizing cells at different stages of the cell cycle showed that chromosome orientation is established prior to the initiation of cell division. Our results indicate that there is a mechanism for orienting the chromosomes and that the chromosome partition protein Spo0J might be part of a bacterial mitotic-like apparatus.

Bipolar localization of the replication origin regions of chromosomes in vegetative and sporulating cells of B. subtilis

To investigate chromosome segregation in B. subtilis, we introduced tandem copies of the lactose operon operator into the chromosome near the replication origin or terminus. We then visualized the position of the operator cassettes with green fluorescent protein fused to the Lac1 repressor. In sporulating bacteria, which undergo asymmetric cell division, origins localized near each pole of the cell whereas termini were restricted to the middle. In growing cells, which undergo binary fission, origins were observed at various positions but preferentially toward the poles early in the cell cycle. In contrast, termini showed little preference for the poles. These results indicate the existence of a mitotic-like apparatus that is responsible for moving the origin regions of newly formed chromosomes toward opposite ends of the cell.

Molecular cloning, expression, and mapping of the high affinity actin-capping domain of chicken cardiac tensin

Tensin, an actin filament capping protein first purified from chicken gizzard, is localized to various types of adherens junctions in muscle and nonmuscle cells. In this paper, we describe the isolation and sequencing of tensin cDNA from a chicken cardiac library. The 6.3-kb chicken cardiac tensin cDNA encodes an open reading frame of 1,792 amino acids. Mammalian cells transfected with the chicken tensin cDNA expressed a polypeptide of approximately 200 kD recognizable by antibodies to chicken gizzard tensin. The expressed protein was incorporated into focal adhesions and other actin-containing structures in the transfected cells. To map the domain associated with tensin's high affinity, barbed-end F-actin-capping activity, bacterially expressed recombinant fusion proteins containing various segments of tensin were prepared and assayed for activity. The results of these experiments show that the high affinity capping domain (kD = 1.3 nM) lies within amino acid residues R1037-V1169. Additional studies on a shorter construct, S1061-H1145, showed that these 85 residues were sufficient for producing complete inhibition of actin polymerization and depolymerization. While this active domain is located within that of the "insertin" sequence (Weigt, C., A. Gaertner, A. Wegner, H. Korte, and H. E. Meyer. 1992. J. Mol. Biol. 227:593-595), our data showing complete inhibition of polymerization and shift in critical concentration are consistent with a simple barbed-end capping mechanism rather than the "insertin model." Our results also differ from those of a recent report (Lo, S. H., P. A. Janmey, J. H. Hartwig, and L. B. Chen. 1994. J. Cell Biol. 125:1067-1075), which concluded that their recombinant tensin has an "insertin-like" inhibitory effect on barbed-end actin polymerization, and that this activity is attributed to residues T936-R1037 (residues 888-989 in their numbering system). In our study, a fusion construct (N790-K1060) encompassing T936-R1037 had no significant effect on actin polymerization and depolymerization, even at high concentrations.

Mechanical properties of cat soleus muscle elicited by sequential ramp stretches: implications for control of muscle

1. Force changes in areflexive cat soleus muscle in decerebrate cats were recorded in response to two sequential constant velocity (ramp) stretches, separated by a variable time interval during which the length was held constant. Initial (i.e., prestretch) background force was generated by activating the crossed-extension reflex, and stretch reflexes were eliminated by section of ipsilateral dorsal roots. 2. For the initial 400-900 microns of the first stretch, the muscle exhibited high stiffness, classically termed "short-range stiffness." This high stiffness region was followed by an abrupt reduction in stiffness, called muscle "yield," after which force remained at a relatively constant level, achieving a plateau in force. This plateau force level depended largely on stretch velocity, but this dependence was much less than proportional to the increase in stretch velocity, in that a 10-fold increase in velocity produced < 2-fold increase in plateau force. 3. In experiments where the velocities of the two sequential ramp stretches were identical, the force plateau level was the same for each stretch, regardless of the time elapsed before the second stretch (varied from 0 to 500 ms). In contrast, measures of stiffness during the initial portion of the second stretch showed time-dependent magnitude reductions. However, stiffness recovered quickly after the first stretch was completed, returning to control values within 30-40 ms. 4. In one preparation, in which the velocities of the two sequential ramp stretches were different, the force plateau elicited during the second stretch exhibited velocity dependence comparable with that recorded in the earlier single velocity studies. Furthermore, muscle yield was still evident in the case where the force change was due solely to the change in velocity and where short-range stiffness had not yet recovered fully from the initial stretch. On the basis of these findings, we argue that the classical descriptions of short-range stiffness and yield are inadequate and that the change in force that has typically been called the muscle yield reflects a transition between short-range, transient elastic behavior to steady-state, essentially viscous behavior. 5. To examine changes in the muscle's mechanical stiffness during single ramp stretches, a single pulse perturbation was superimposed at various times before, during, and subsequent to the constant velocity stretch. The force increment elicited in response to each pulse decreased relative to the initial isometric value, remained essentially constant until the end of the ramp, and then returned to its prestretch magnitude shortly (30-40 ms) after stretch termination.(ABSTRACT TRUNCATED AT 400 WORDS)

Nuclear morphometry and its prognostic significance in laryngeal squamous cell carcinomas

The five parameters including nuclear area (NA), nuclear perimeter (NP), nuclear diameter (ND), axis ratio and nuclear roundness were evaluated with MIAS200 Image Analysis System (Sichuan University, Chengdu) in 45 patients with laryngeal primary squamous cell carcinoma, which were confirmed pathologically and operated on from January 1977 to October 1987. The results showed that NA, NP and ND are important prognostic indicators. The survival rate in patients with large nuclei (NA greater than 73 microns2, NP greater than 32.5 microns, ND greater than 12 microns) was significantly lower than that in those with small nuclei (NA less than 73 microns2, NP less than 32.5 microns, ND less than 12 microns) (P less than 0.0025). These findings strongly suggest that patients with laryngeal squamous cell carcinoma with large nuclei should be treated more aggressively.

A quantitative analysis of pendular motion of the lower leg in spastic human subjects

The purpose of this study was to examine gravity-induced oscillations of the lower leg in normal and spastic subjects, with a view towards evaluating a clinical test of spasticity called the "pendulum" test. Motivations for studying the pendulum test were to determine if realistic aspects of spasticity and neuromuscular control could be incorporated into a description of the motion, and to better understand the underlying neurophysiological disturbances in spasticity. For passive limb motion (in which no reflex excitation occurred), a second-order linear model did not provide an adequate description of the motion for either spastic or normal legs. Instead, system equations including nonlinear mechanical properties simulating asymmetries in the swing and amplitude dependent variations in stiffness and damping provided a more accurate description. For spastic limb motion (in which reflex excitation did occur), accurate simulation required components accounting for abnormal reflex activation, coinciding with the time course of EMG activation. These included increased stiffness and damping with their gains related to reflex EMG magnitude, and changes in the rest length of the stiffness. Comparison of numerical solutions of the equations with experimental data showed our nonlinear model simulated the motion accurately, with the variance accounted for usually exceeding 90%.

beta-Hydroxydecanoylthioester dehydrase: a rapid, convenient, and accurate product distribution assay

High-performance liquid chromatography on silica gel has been used to separate the products from incubation of substrates with beta-hydroxydecanoylthioester dehydrase (Escherichia coli). Peaks are detected by their absorbances at 230 nm. Following correction for differences in extinction coefficients, comparison of the peak areas reveals the relative amounts of beta-hydroxydecanoate, E-2-decenoate, and Z-3-decenoate thioesters of N-acetylcysteamine.

On the mechanism for inactivation of cytochalasin binding activity associated with F-actin and spectrin-band 4.1-actin complex by sulfhydryl reagents

The sulfhydryl group modifying reagent, p-hydroxymercuribenzoate, inhibited the cytochalasin binding activity of the actin nuclei in the spectrin-band 4.1-actin complex from the erythrocyte membrane and of muscle F-actin. Kinetic studies indicated that while the cytochalasin binding activity was immediately inhibited, the actin remained filamentous and depolymerized slowly over a period of 1 to 2 h. Scatchard analysis of the binding data revealed that initially only the KD was affected. However, prolonged incubation led to depolymerization of the F-actin and dissociation of the spectrin-band 4.1-actin complex, resulting in loss of binding sites. It thus appears that certain actin sulfhydryl group(s) are important for cytochalasin binding. However, the most reactive sulfhydryl group (cys-374) on actin does not appear to be involved.

Complexes containing actin and spectrin from erythrocyte and brain

A complex of proteins with properties similar to those of erythrocyte spectrin-band 4.1-actin complex has been identified in a preparation derived from bovine brain. The complex has an apparent sedimentation coefficient of about 26S, and contains brain spectrin (also called fodrin) and actin as major components. The actin in the complex is in the oligomeric form, which nucleates assembly of actin filaments that grow from the "barbed" end. The complex cross-links actin filaments, resulting in an increase in low-shear viscosity. Whether the complex contains a protein analogous to erythrocyte band 4.1 is not known. However, it can be demonstrated that brain spectrin has the capability to interact with band 4.1 in a way which increases its ability to cross-link actin filaments.

The capactins, a class of proteins that cap the ends of actin filaments

A number of proteins that bind specifically to the barbed ends of actin filaments in a cytochalasin-like manner have been purified to various degrees from a variety of muscle and non-muscle cells and tissues. Preliminary evidence also indicates that proteins that interact with the pointed ends of filaments are present in skeletal muscle. Because of their ability to cap one or the other end of an actin filament, we have designated this class of proteins as the 'capactins'. On the basis of their effect on actin filament assembly and interaction in vitro, we propose that the capactins play important roles in cellular regulation of actin-based cytoskeletal and contractile functions. Our finding that the disappearance of actin filament bundles in virally transformed fibroblasts can be correlated with an increase in capactin activity in the extracts of these cells is consistent with this hypothesis.

Spectrin-4.1-actin complex of the human erythrocyte: molecular basis of its ability to bind cytochalasins with high-affinity and to accelerate actin polymerization in vitro

The spectrin-4.1-actin complex isolated from the cytoskeleton of human erythrocyte was found to be similar to muscle F-actin in several aspects: Both the complex and F-actin nucleate cytochalasin-sensitive actin polymerization; both bind dihydrocytochalasin B with similar binding contrasts; both can be depolymerized by DNase I with loss of cytochalasin binding activity. From these results, we conclude that the actin in the complex is in an oligomeric form. However, the presence of spectrin and band 4.1 in the complex not only stabilized the actin in the complex as evidenced by its resistance to depolymerization in low-ionic-strength conditions and to DNase I as compared with F-actin, but also altered the characteristics of the binding site(s) for cytochalasins believed to be located at the "barbed" (polymerizing) end of the oligomeric actin.