Close Physical Relationship Research Articles

Mitochondrial division inhibitor 1 (mdivi-1) increases oxidative capacity and contractile stress generated by engineered skeletal muscle.

In skeletal muscle fibers, mitochondria are densely packed adjacent to myofibrils because adenosine triphosphate (ATP) is needed to fuel sarcomere shortening. However, despite this close physical and biochemical relationship, the effects of mitochondrial dynamics on skeletal muscle contractility are poorly understood. In this study, we analyzed the effects of Mitochondrial Division Inhibitor 1 (mdivi-1), an inhibitor of mitochondrial fission, on the structure and function of both mitochondria and myofibrils in skeletal muscle tissues engineered on micromolded gelatin hydrogels. Treatment with mdivi-1 did not alter myotube morphology, but did increase the mitochondrial turbidity and oxidative capacity, consistent with reduced mitochondrial fission. Mdivi-1 also significantly increased basal, twitch, and tetanus stresses, as measured using the Muscular Thin Film (MTF) assay. Finally, mdivi-1 increased sarcomere length, potentially due to mdivi-1-induced changes in mitochondrial volume and compression of myofibrils. Together, these results suggest that mdivi-1 increases contractile stress generation, which may be caused by an increase in maximal respiration and/or sarcomere length due to increased volume of individual mitochondria. These data reinforce that mitochondria have both biochemical and biomechanical roles in skeletal muscle and that mitochondrial dynamics can be manipulated to alter muscle contractility.

Shank2 Binds to aPKC and Controls Tight Junction Formation with Rap1 Signaling during Establishment of Epithelial Cell Polarity

Epithelial cells establish apicobasal polarity by forming tight junctions (TJs) at the apical-lateral boundary, which play fundamental roles in physiological functions. An evolutionarily conserved atypical protein kinase C (aPKC)-partitioning defective (PAR) complex functions as a platform for TJ assembly during cell polarity establishment. However, how this complex converts the spatial cues into a subsequent active unit is unclear. Here, we identify an epithelial isoform of Shank2 as a mediator of the aPKC-PAR complex. Shank2 binds to and colocalizes with aPKC at apical junctional regions of polarized epithelial cells. Shank2 knockdown results in defects in TJ formation. Mechanistically, we find that the N-terminal SPN domain is required for the junctional localization of Shank2 and binds to the active form of Rap1 small GTPase, which is involved in TJ formation. Our findings suggest that a close physical and functional relationship between aPKC and Shank2-active Rap1 signaling serves as the platform for TJ assembly to regulate epithelial cell polarity.

Mandibular squamous odontogenic tumour misdiagnosed as squamous cell carcinoma: a case report and review of literature

Squamous odontogenic tumor (SOT) is an unusual, benign odontogenic tumor presented in close physical relationship to the dentition and originating from the epithelial rests of Malassez in the periodontal ligament or gingival epithelium. It was first described in 1975 by Pullon et al. and there are few cases reported in the literature. The main characteristic of this lesion is a tendency to arise in the molar region of the mandible and in the premolar-canine region of the maxilla with a simultaneously asymptomatic swelling in the alveolar. SOTs are incidental discoveries on routine dental radiographs or panoramic x-rays in many cases. We report a case of a 60-year-old Caucasian woman with SOT of the mandible in the area of the right premolars.

Connexin 50 and AQP0 are Essential in Maintaining Organization and Integrity of Lens Fibers.

PurposeConnexins and aquaporins play essential roles in maintaining lens homeostasis and transparency and there is a close physical and functional relationship between these two proteins. Aquaporin 0 (AQP0), in addition to its role in water transport in the lens, acts as a cell–cell adhesion molecule. Recently, we showed a new role of connexin (Cx) 50 in mediating cell–cell adhesion. However, the cooperative roles of these two proteins in the lens in vivo have not been reported.MethodsWe generated an AQP0/Cx50 double knockout (dKO) mouse model. Light, fluorescence, transmission thin section, and freeze-fracture electron microscopy, as well as wheat germ agglutinin and phalloidin labeling were used to evaluate lens structure. Mechanical properties of lenses were determined by mechanical compression testing.ResultsDKO mice exhibited small eyes and lenses with severe cataracts, along with lens posterior defects, including posterior capsule rupture. The dKO mouse lenses had severe structural disruption associated with increased spaces between lens fiber cells when compared with wild-type lenses or lenses deficient in either Cx50 or AQP0. DKO mice also exhibited greater reduction in lens size compared with Cx50 KO mice. Gap-junction plaque size was greatly decreased in cortical fiber cells in dKO mice. Moreover, lens stiffness and elasticity were completely diminished, exhibiting a gelatinous texture in adult dKO mice.ConclusionsThis novel mouse model reveals that Cx50 and AQP0 play an important role in mediating cell–cell adhesion function in the lens fiber cells and their deficiency impairs lens fiber organization, integrity, mechanical properties, and lens development.

Horizontal transfer of a retrotransposon between parasitic nematodes and the common shrew

BackgroundAs the genomes of more metazoan species are sequenced, reports of horizontal transposon transfers (HTT) have increased. Our understanding of the mechanisms of such events is at an early stage. The close physical relationship between a parasite and its host could facilitate horizontal transfer. To date, two studies have identified horizontal transfer of RTEs, a class of retrotransposable elements, involving parasites: ticks might act as vector for BovB between ruminants and squamates, and AviRTE was transferred between birds and parasitic nematodes.ResultsWe searched for RTEs shared between nematode and mammalian genomes. Given their physical proximity, it was necessary to detect and remove sequence contamination from the genome datasets, which would otherwise distort the signal of horizontal transfer. We developed an approach that is based on reads instead of genomic sequences to reliably detect contamination. From comparison of 43 RTEs across 197 genomes, we identified a single putative case of horizontal transfer: we detected RTE1_Sar from Sorex araneus, the common shrew, in parasitic nematodes. From the taxonomic distribution and evolutionary analysis, we show that RTE1_Sar was horizontally transferred.ConclusionWe identified a new horizontal RTE transfer in host-parasite interactions, which suggests that it is not uncommon. Further, we present and provide the workflow a read-based method to distinguish between contamination and horizontal transfer.

Unconfined Compressive Strength Properties of a Cement- Organic Soil Composite

Laboratory strength testing of the mixtures is a necessary stage of soil stabilisation. They enable assessment of the impact of binders on the improvement of the properties of stabilised organic soil, which is extremely useful for the development and verification of the correct composition of the soil-binder composite used in situ. The paper presents selected results of unconfined compressive strength tests of a cement-organic composite depending on the quantity of the cement binder and the different organic matter content. The laboratory testing comprised 20 different mixture designs in which the independent variables were the organic matter content (Iom) and the ratio of added cement to the dry weight of soil (mc/ms): the Iom ranged from 20% to 84.40% and the mc/ms from 0.75 to 2.75. Measurements of the unconfined compressive strength were conducted on more than 150 cylindrical specimens after 7 and 28 days of curing. Analysis of the obtained strength test results shows that there is a close physical relationship between the geotechnical properties of the components and the parameter of unconfined compressive strength of organic soil-cement binder mixtures

Ca2+ release via two-pore channel type 2 (TPC2) is required for slow muscle cell myofibrillogenesis and myotomal patterning in intact zebrafish embryos

We recently demonstrated a critical role for two-pore channel type 2 (TPC2)-mediated Ca2+ release during the differentiation of slow (skeletal) muscle cells (SMC) in intact zebrafish embryos, via the introduction of a translational-blocking morpholino antisense oligonucleotide (MO). Here, we extend our study and demonstrate that knockdown of TPC2 with a non-overlapping splice-blocking MO, knockout of TPC2 (via the generation of a tpcn2dhkz1a mutant line of zebrafish using CRISPR/Cas9 gene-editing), or the pharmacological inhibition of TPC2 action with bafilomycin A1 or trans-ned-19, also lead to a significant attenuation of SMC differentiation, characterized by a disruption of SMC myofibrillogenesis and gross morphological changes in the trunk musculature. When the morphants were injected with tpcn2-mRNA or were treated with IP3/BM or caffeine (agonists of the inositol 1,4,5-trisphosphate receptor (IP3R) and ryanodine receptor (RyR), respectively), many aspects of myofibrillogenesis and myotomal patterning (and in the case of the pharmacological treatments, the Ca2+ signals generated in the SMCs), were rescued. STED super-resolution microscopy revealed a close physical relationship between clusters of RyR in the terminal cisternae of the sarcoplasmic reticulum (SR), and TPC2 in lysosomes, with a mean estimated separation of ~52–87nm. Our data therefore add to the increasing body of evidence, which indicate that localized Ca2+ release via TPC2 might trigger the generation of more global Ca2+ release from the SR via Ca2+-induced Ca2+ release.

Adipogenic role of alternatively activated macrophages in β-adrenergic remodeling of white adipose tissue.

De novo brown adipogenesis involves the proliferation and differentiation of progenitors, yet the mechanisms that guide these events in vivo are poorly understood. We previously demonstrated that treatment with a β3-adrenergic receptor (ADRB3) agonist triggers brown/beige adipogenesis in gonadal white adipose tissue following adipocyte death and clearance by tissue macrophages. The close physical relationship between adipocyte progenitors and tissue macrophages suggested that the macrophages that clear dying adipocytes might generate proadipogenic factors. Flow cytometric analysis of macrophages from mice treated with CL 316,243 identified a subpopulation that contained elevated lipid and expressed CD44. Lipidomic analysis of fluorescence-activated cell sorting-isolated macrophages demonstrated that CD44+ macrophages contained four- to five-fold higher levels of the endogenous peroxisome-proliferator activated receptor gamma (PPARγ) ligands 9-hydroxyoctadecadienoic acid (HODE), and 13-HODE compared with CD44- macrophages. Gene expression profiling and immunohistochemistry demonstrated that ADRB3 agonist treatment upregulated expression of ALOX15, the lipoxygenase responsible for generating 9-HODE and 13-HODE. Using an in vitro model of adipocyte efferocytosis, we found that IL-4-primed tissue macrophages accumulated lipid from dying fat cells and upregulated expression of Alox15. Furthermore, treatment of differentiating adipocytes with 9-HODE and 13-HODE potentiated brown/beige adipogenesis. Collectively, these data indicate that noninflammatory removal of adipocyte remnants and coordinated generation of PPARγ ligands by M2 macrophages provides localized adipogenic signals to support de novo brown/beige adipogenesis.

Vascular geometry and oxygen diffusion in the vicinity of artery-vein pairs in the kidney.

Renal arterial-to-venous (AV) oxygen shunting limits oxygen delivery to renal tissue. To better understand how oxygen in arterial blood can bypass renal tissue, we quantified the radial geometry of AV pairs and how it differs according to arterial diameter and anatomic location. We then estimated diffusion of oxygen in the vicinity of arteries of typical geometry using a computational model. The kidneys of six rats were perfusion fixed, and the vasculature was filled with silicone rubber (Microfil). A single section was chosen from each kidney, and all arteries (n = 1,628) were identified. Intrarenal arteries were largely divisible into two "types," characterized by the presence or absence of a close physical relationship with a paired vein. Arteries with a close physical relationship with a paired vein were more likely to have a larger rather than smaller diameter, and more likely to be in the inner-cortex than the mid- or outer cortex. Computational simulations indicated that direct diffusion of oxygen from an artery to a paired vein can only occur when the two vessels have a close physical relationship. However, even in the absence of this close relationship oxygen can diffuse from an artery to periarteriolar capillaries and venules. Thus AV oxygen shunting in the proximal preglomerular circulation is dominated by direct diffusion of oxygen to a paired vein. In the distal preglomerular circulation, it may be sustained by diffusion of oxygen from arteries to capillaries and venules close to the artery wall, which is subsequently transported to renal veins by convection.

PP118: Squamous odontogenic tumour: Report of a rare case and review of the literature

Squamous odontogenic tumour (SOT) was first described in 1975, by Pullon et al. as a rare, benign odontogenic tumor arising in close physical relationship to the dentition from the epithelial rests of Malassez in the periodontal ligament or gingival epithelium. To date, less than 50 cases have been described in the literature. We describe a case of SOT which was histologically misdiagnosed as a metastatic carcinoma of unknown origin. In the discussion and review of the literature that follows, the features of SOT, the differential diagnosis and the appropriate treatment are described.

PTSD Symptoms in Young Children Exposed to Intimate Partner Violence

Intimate partner violence (IPV) places infants and young children at risk for development of trauma symptoms. However, this is an understudied consequence of IPV because young children pose particular difficulties for assessment of trauma symptoms. The authors collected maternal reports on mothers' and children's posttraumatic stress disorder (PTSD) symptoms and IPV yearly, from ages 1 to 7. Approximately half of the children exposed to IPV at each time period developed some trauma symptoms, and frequency of IPV witnessed was associated with PTSD symptoms. Maternal and child PTSD symptoms were correlated, suggesting that young children may be particularly vulnerable to relational PTSD due to their close physical and emotional relationship with their parents.

Exotic mitotic mechanisms

The emergence of eukaryotes around two billion years ago provided new challenges for the chromosome segregation machineries: the physical separation of multiple large and linear chromosomes from the microtubule-organizing centres by the nuclear envelope. In this review, we set out the diverse solutions that eukaryotic cells use to solve this problem, and show how stepping away from ‘mainstream’ mitosis can teach us much about the mechanisms and mechanics that can drive chromosome segregation. We discuss the evidence for a close functional and physical relationship between membranes, nuclear pores and kinetochores in generating the forces necessary for chromosome segregation during mitosis.

Dynamic CpG-DNA Methylation of Il10 and Il19 in CD4+ T Lymphocytes and Macrophages: Effects on Tissue-Specific Gene Expression

The IL-10 family of cytokines consists of 9 members, including the immune-regulatory IL-10; Il19 is in close physical relationship with Il10 in the so-called IL-10 cytokine cluster on chromosome 1q32. While IL-10 is ubiquitously expressed, IL-19 expression is restricted to myeloid and epithelial cells. Little is known about molecular mechanisms that control tissue-specific expression of IL-10, and IL-19. Modifications in CpG-DNA methylation are a key mechanism in controlling transcription. Using bisulfite sequencing, we demonstrate that murine Il19 is methylated in CD4+ T lymphocytes. Macrophages display site-specific demethylation of Il19. The ubiquitously expressed Il10 gene is methylated to a lower degree and exhibits tissue-specific methylation patterns. DNA demethylation with 5-azacytidine resulted in an induction of IL-10, and IL-19 expression in CD4+ T cells, and CpG-DNA methylation through DNMT3a resulted in transcriptional silencing in macrophages. Thus, our findings suggest a role of CpG-DNA methylation in the regulation of Il10 and Il19.

23 Mitochondrial motility and vascular smooth muscle proliferation

Mitochondrial function is critical for multiple facets of cellular function including ATP production and calcium handling. Subcellular location of the organelle is important for function. In smooth muscle, mitochondria modulate...

Fis1, Bap31 and the kiss of death between mitochondria and endoplasmic reticulum

Dynamic structural and functional liaisons between mitochondria and the endoplasmic reticulum (ER) support a wide range of cell functions, including the ability of the cell to kill itself by apoptosis. A new study in this issue of The EMBO Journal sheds light on how these interactions regulate Bax/Bak‐driven cell death within the complex milieu of the cell, suggesting that mitochondria–ER dynamics can involve an unanticipated two‐way communication in cell death, from mitochondria to ER and back again. Much of our knowledge on apoptosis induction in higher organisms, which revolves around mitochondria and proapoptotic Bcl‐2 family members such as Bax or Bak, has derived from reconstitution studies using biochemical and genetically defined systems. These studies revealed step‐wise activation of Bax/Bak in the mitochondrial outer membrane by activator BH3‐only proteins, regulated by prosurvival Bcl‐2 family proteins as well as by sensitizing BH3‐only proteins. In the complex environment of the intact cell, however, where the potential for competing reactions is enormous, the question of efficiencies and specificities takes precedence. As a consequence, there exists a large array of supporting players to ensure rapid and orderly cell demise by the Bax/Bak mechanism. Not surprisingly, many of these supporting roles involve mitochondrial biology—in particular, mitochondrial fusion/fission dynamics as well as the close physical and functional relationship of the mitochondrion with …

Mitochondrial Motility During Vascular Smooth Muscle Proliferation

Mitochondrial function is critical for multiple facets of cellular function, including ATP production and Ca2+ handling. Subcellular location of the organelle is important for function. For example, in smooth muscle, mitochondria modulate Ca2+ signals arising from the inositol-trisphosphate-sensitive channels (IP3R), even at the level of Ca2+ puffs, revealing a close physical relationship between IP3R and mitochondria. This relationship seems incompatible with rapid free movement of mitochondria-observed in several cell types. Here we report mitochondria in freshly-isolated smooth muscle cells lacked directed motion and Brownian-like movement was limited so that no displacement of individual organelles occurred. The movement did not change by disruption of actin polymerisation (latrunculin-B, 10 μM), inhibition of microtubule polymerisation (nocodazole, 10 μM) or removal of Ca2+ from the extra-cellular solution. In intact pressurised (40 mmHg) cerebral arteries, individual mitochondria within the smooth muscle were largely stationary; however in a small but significant number of cells mitochondria displayed directed movements. When these arteries were maintained in conditions which promote cell proliferation, an increased number of cells showing moving mitochondria and an increase in the extent of movement occurred. We postulated that those smooth muscle cells displaying motile mitochondria may be proliferative, as downregulation of the mitochondrial tether mitofusin-2 has been reported in proliferative vascular disease. In support, within days of allowing freshly-isolated cerebral artery smooth muscle cells to proliferate in culture, extensive mitochondrial motility developed. A spectrum of movements was observed: long- and short-distance directed movements, wiggling, looping, extension, retraction, and Brownian-like diffusion. Therefore, when isolated smooth muscle cells are allowed to proliferate, mitochondria switch from being static, with no observed motion (that suggests physical confinement), to being highly mobile and unconfined organelles. This increased mitochondrial mobility may contribute to the altered Ca2+ signalling observed in proliferative smooth muscle.

Complex and inconsistent patterns of variation in benthos, micro-algae and sediment over multiple spatial scales

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 398:33-47 (2010) - DOI: https://doi.org/10.3354/meps08328 Complex and inconsistent patterns of variation in benthos, micro-algae and sediment over multiple spatial scales M. G. Chapman*, T. J. Tolhurst, R. J. Murphy, A. J. Underwood Centre for Research on Ecological Impacts of Coastal Cities, Marine Ecology A11, University of Sydney, New South Wales 2006, Australia *Email: gee@bio.usyd.edu.au ABSTRACT: Because of their close physical relationship, it is often assumed that there are strong functional relationships between sediments and biota. Yet, there have been few studies of the characteristics of sediments over multiple spatial scales, despite evidence that micro-algae and macro- and meiofauna vary greatly at cm to km scales. This study quantified variability in macrofauna, micro-algae, and physical and biochemical properties of sediments over scales from 50 cm to km. The benthos was most variable at small scales and, even where there were large mean differences in abundance at large scales, these were small compared to the variation from plot to plot along a shore. Only 1 of 24 analyses showed larger variation at the scale of km than that found at 50 cm. Some measures of microphytobenthos showed large variation at the scale of 100s m or more, but other measures of the same flora did not show similar patterns. Concentrations of sand were consistent at different depths and at large scales, but concentrations of mud were more variable within than among shores. Neither sand nor mud correlated significantly with most biochemical properties of sediments. For sediments, variation at the scale of km was only larger than that of 50 cm in 13 of 57 analyses. To understand the relative importance of ecological processes in determining distributions and abundances, it is important to get quantitative data on the scales at which organisms or habitats vary. These are the scales at which ecological processes are likely to have large effects because large-scale processes are unlikely to explain variation at much smaller scales. The importance of small-scale variability in sediments and the associated biota is discussed in terms of sampling protocols for understanding ecological processes, or for assessing impact or restoration. KEY WORDS: Intertidal soft sediment · Microphytobenthos · Benthic assemblage · Spatial patterns · Components of variation · Scales Full text in pdf format PreviousNextCite this article as: Chapman MG, Tolhurst TJ, Murphy RJ, Underwood AJ (2010) Complex and inconsistent patterns of variation in benthos, micro-algae and sediment over multiple spatial scales. Mar Ecol Prog Ser 398:33-47. https://doi.org/10.3354/meps08328 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 398. Online publication date: January 05, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Mapping of the Saccharomyces cerevisiae Oxa1-Mitochondrial Ribosome Interface and Identification of MrpL40, a Ribosomal Protein in Close Proximity to Oxa1 and Critical for Oxidative Phosphorylation Complex Assembly

The Oxa1 protein plays a central role in facilitating the cotranslational insertion of the nascent polypeptide chains into the mitochondrial inner membrane. Mitochondrially encoded proteins are synthesized on matrix-localized ribosomes which are tethered to the inner membrane and in physical association with the Oxa1 protein. In the present study we used a chemical cross-linking approach to map the Saccharomyces cerevisiae Oxa1-ribosome interface, and we demonstrate here a close association of Oxa1 and the large ribosomal subunit protein, MrpL40. Evidence to indicate that a close physical and functional relationship exists between MrpL40 and another large ribosomal protein, the Mrp20/L23 protein, is also provided. MrpL40 shares sequence features with the bacterial ribosomal protein L24, which like Mrp20/L23 is known to be located adjacent to the ribosomal polypeptide exit site. We propose therefore that MrpL40 represents the Saccharomyces cerevisiae L24 homolog. MrpL40, like many mitochondrial ribosomal proteins, contains a C-terminal extension region that bears no similarity to the bacterial counterpart. We show that this C-terminal mitochondria-specific region is important for MrpL40's ability to support the synthesis of the correct complement of mitochondrially encoded proteins and their subsequent assembly into oxidative phosphorylation complexes.

Nerve fiber analysis of ansa cervicalis–vagus communications

Communications between the ansa cervicalis and the vagus nerve, although described only as variations in many textbooks, can be observed frequently in the dissection room. Following macroscopic observation, some of such cases were subsequently dissected under surgical microscope to determine the nature of such communications. As a result, two broad categories of communications between the ansa cervicalis complex and the vagus nerve could be recognized: (i) false (pseudo) communications, where the two nerves were attached only by the connective tissue with no fiber exchange; and (ii) true communications, with nerve fiber involvement. Fiber analysis showed that the majority of the ansa-vagal communications observed during gross dissection were of the first category. True communications, when present, were only scanty contributions and always directed towards the side of the vagus. In addition, the vagus (region of the inferior ganglion) and hypoglossal nerves were found to be in close contact at the base of the skull and usually could not be separated by gross dissection. But such attachments, too, were shown to be almost entirely of false nature except for the possible presence of a few fine nerve filaments. It seems that the ansa-vagal communications are merely a result of the close physical relationship between the two structures and serve no significant functional purpose, but at the same time may hinder the prospects of using ansa cervicalis in surgical procedures such as re-innervation of laryngeal and facial muscles, following damage to recurrent laryngeal and facial nerves, respectively.

Magnetic Twist of an Extreme‐Ultraviolet Coronal Loop Inferred from Plasma Constriction

Magnetic twist is a very likely way of constricting coronal plasma into loops. An attempt is made to determine the magnetic twist that can explain the constriction of coronal loops indirectly from observations. We decompose the coronal magnetic field into a large-scale magnetic field and a small-scale magnetic field. The large-scale field is assumed to be force-free, but the small-scale field is not. We derive a magnetohydrostatic equation describing the relationship between the small-scale field variation and the pressure variation across the loop. We adopt a simple flux rope model with the following properties. (1) There exists a close physical relationship between the twist-creating process and the plasma-injecting process that keeps the axial field constant as the loop forms. (2) The large-scale force-free field is so close to the current-free configuration that its associated current is negligible in the plasma constriction. (3) Pressure peaks on the loop axis and monotonically decreases with the distance from the axis. This flux tube model is characterized by three independent parameters: axial field strength, peak pressure excess, and loop width. The peak pressure excess and the loop width are determined from an analysis of the EUV data taken by TRACE, and an estimate of the axial field strength is found from the linear force-free extrapolation of the photospheric magnetic field observed by SOHO MDI. By applying this method to a specific coronal loop, we have found that the magnetic twist on the loop axis is about 1.5π, and the twist per unit length is more concentrated near its top than near its footpoints. This twist value has been obtained using the simplifying assumption of uniform axial field strength. In the case where the axial field is stronger inside the loop than in the surroundings, the twist will turn out to be greater than 1.5π, since the twist is required to constrict not only the plasma but also the magnetic flux. On the other hand, if the axial field is weaker than that in the surroundings, a smaller twist may be enough to constrict the plasma.