High hydrostatic pressure effects in vivo: changes in cell morphology, microtubule assembly, and actin organization

Positive selection in cilia-related genes may facilitate deep-sea adaptation of Thermocollonia jamsteci

Deep-sea hydrothermal vents are characterized by high hydrostatic pressure, hypoxia, darkness and toxic substances. However, how organisms adapt to such extreme marine ecosystems remain poorly understood. We hypothesize that adaptive evolution plays an essential role in generating novelty for evolutionary adaptation to the deep-sea environment because adaptive evolution has been found to be critical for species origin and evolution. In this project, the chromosome-level genome of the deep-sea hydrothermal vent gastropod T. jamsteci was constructed for the first time to examine molecular mechanisms of its adaptation to the deep-sea environment. The genome size was large (2.54 Gb), ranking at the top of all species in the Vetigastropoda subclass, driven primarily by the bursts of transposable elements (TEs). The transposition of TEs may also trigger chromosomal changes including both inter-chromosomal fusions and intra-chromosomal activities involving chromosome inversions, rearrangements and fusions, as revealed by comparing the genomes of T. jamsteci and its closely related shallow-sea species Gibbula magus. Innovative changes including the expansion of the ABC transporter gene family that may facilitate detoxification, duplication of genes related to endocytosis, immunity, apoptosis, and anti-apoptotic domains that may help T. jamsteci fight against microbial pathogens, were identified. Furthermore, comparative analysis identified positive selection signals in a large number of genes including the hypoxia up-regulated protein 1, which is a chaperone that may promote adaptation of the T. jamsteci to hypoxic deepsea environments, hox2, Rx2, Pax6 and cilia-related genes BBS1, BBS2, BBS9 and RFX4. Notably, because of the critical importance of cilia and IFT in development, positive selection in cilia-related genes may play a critical role in facilitating T. jamsteci to adapt to the high-pressure deep-sea ecosystem. Results from this study thus revealed important molecular clues that may facilitate further research on the adaptation of molluscs to deep-sea hydrothermal vents.

Cellular transfection using rapid decrease in hydrostatic pressure

Of all methods exercised in modern molecular biology, modification of cellular properties through the introduction or removal of nucleic acids is one of the most fundamental. As such, several methods have arisen to promote this process; these include the condensation of nucleic acids with calcium, polyethylenimine or modified lipids, electroporation, viral production, biolistics, and microinjection. An ideal transfection method would be (1) low cost, (2) exhibit high levels of biological safety, (3) offer improved efficacy over existing methods, (4) lack requirements for ongoing consumables, (5) work efficiently at any scale, (6) work efficiently on cells that are difficult to transfect by other methods, and (7) be capable of utilizing the widest array of existing genetic resources to facilitate its utility in research, biotechnical and clinical settings. To address such issues, we describe here Pressure-jump-poration (PJP), a method using rapid depressurization to transfect even difficult to modify primary cell types such as embryonic stem cells. The results demonstrate that PJP can be used to introduce an array of genetic modifiers in a safe, sterile manner. Finally, PJP-induced transfection in primary versus transformed cells reveals a surprising dichotomy between these classes which may provide further insight into the process of cellular transformation.

Genomic Analysis of a Scale Worm Provides Insights into Its Adaptation to Deep-Sea Hydrothermal Vents

Deep-sea polynoid scale worms endemic to hydrothermal vents have evolved an adaptive strategy to the chronically hypoxic environment, but its underlying molecular mechanisms remain elusive. Here, we assembled a chromosome-scale genome of the vent-endemic scale worm Branchipolynoe longqiensis (the first annotated genome in the subclass Errantia) and annotated two shallow-water polynoid genomes, aiming to elucidate the adaptive mechanisms. We present a genome-wide molecular phylogeny of Annelida which calls for extensive taxonomy revision by including more genomes from key lineages. The B. longqiensis genome with a genome size of 1.86 Gb and 18 pseudochromosomes is larger than the genomes of two shallow-water polynoids, possibly due to the expansion of various transposable elements (TEs) and transposons. We revealed two interchromosomal rearrangements in B. longqiensis when compared with the two shallow-water polynoid genomes. The intron elongation and interchromosomal rearrangement can influence a number of biological processes, such as vesicle transport, microtubules, and transcription factors. Furthermore, the expansion of cytoskeleton-related gene families may favor the cell structure maintenance of B. longqiensis in the deep ocean. The expansion of synaptic vesicle exocytosis genes has possibly contributed to the unique complex structure of the nerve system in B. longqiensis. Finally, we uncovered an expansion of single-domain hemoglobin and a unique formation of tetra-domain hemoglobin via tandem duplications, which may be related to the adaptation to a hypoxic environment.

Technologies for Vitrification Based Cryopreservation

Cryopreservation is a unique and practical method to facilitate extended access to biological materials. Because of this, cryopreservation of cells, tissues, and organs is essential to modern medical science, including cancer cell therapy, tissue engineering, transplantation, reproductive technologies, and bio-banking. Among diverse cryopreservation methods, significant focus has been placed on vitrification due to low cost and reduced protocol time. However, several factors, including the intracellular ice formation that is suppressed in the conventional cryopreservation method, restrict the achievement of this method. To enhance the viability and functionality of biological samples after storage, a large number of cryoprotocols and cryodevices have been developed and studied. Recently, new technologies have been investigated by considering the physical and thermodynamic aspects of cryopreservation in heat and mass transfer. In this review, we first present an overview of the physiochemical aspects of freezing in cryopreservation. Secondly, we present and catalog classical and novel approaches that seek to capitalize on these physicochemical effects. We conclude with the perspective that interdisciplinary studies provide pieces of the cryopreservation puzzle to achieve sustainability in the biospecimen supply chain.

Adaptation and evolution of the sea anemone Alvinactis sp. to deep‐sea hydrothermal vents: A comparison using transcriptomes

Sea anemones are diverse and ecologically successful members of Anthozoa. They are often found in intertidal and shallow waters, although a few of them inhabit harsher living conditions, such as deep‐sea hydrothermal vents. Here, we sequenced the transcriptome of the vent sea anemone Alvinactis sp., which was collected from Edmond vent along the central Indian Ocean ridge at a depth of 3275 m, to explore the molecular mechanisms related to adaptation to vents. Compared with another deep‐sea anemone (Paraphelliactis xishaensis) and five shallow water sea anemones, a total of 117 positively selected genes and 46 significantly expanded gene families were found in Alvinactis sp. specifically that may be related to its vent‐specific aspect of adaptation. In addition, 127 positively selected genes and 23 significantly expanded gene families that were found in both Alvinactis sp. and P. xishaensis. Among these, vent‐specific adaptations of Alvinactis sp. may involve genetic alterations in peroxisome, ubiquitin‐mediated protein degradation, oxidative phosphorylation, and endocytosis, and its deep‐sea adaptation may involve changes in genetic information processing. Differentially expressed genes between Alvinactis sp. and the deep‐sea anemone P. xishaensis were enriched in a variety of pathways related to adaptation, such as energy metabolism, genetic information processing, endocytosis, and peroxisomes. Overall, we provided the first transcriptome of sea anemones that inhabit vents, which enriches our knowledge of deep‐sea hydrothermal vent adaptation and the diversity of sea anemones.

Effect of intermittent hydrostatic pressure on aging human chondrocyte cells

In this study, a hydrostatic pressure chamber (HPC) is designed and developed to host chondrocyte cell culture. External stimuli such as forces, pressure, vibration etc. are found to be significant factors on upregulating the relevant proteins for constructing the extracellular matrix (ECM) during culturing. The aim of this paper is to design a system which provides external stimuli during chondrocyte cell culture as well as to discover the relevant gene which can generate the repair and regeneration of aging cells. The system consists of a controllable HPC that provides intermittent hydrostatic pressure (HP) on the cultured cells. The chamber is capable of applying intermittent HP in the range: 0 to1 MPa, at a frequency of 0.5-1Hz. An investigation was undertaken to determine the improvement of human chondrocyte cells viz. of 3 sub-jects whose ages are 60 and above. The effect of HP on the aging cells is observed through the extracted ribonucleic acid (RNA) after the cell is treated with HP for two hours, each day, over four days. The experiments were conducted to observe the effect of HP on the level of collagen type I, collagen type II, and aggrecan. Results show that HP did little to help in upregulating the aggrecan and collagen type II in aged-chondrocyte cells. Further, it was found that the application of HP depended on the number of days applied. The results presented the possibility of ap-plying HP in regeneration of damaged cartilage in elderly.

Pressure-induced changes on the morphology and gene expression in mammalian cells

We evaluated the effect of high hydrostatic pressure on mouse embryonic fibroblasts (MEFs) and mouse embryonic stem (ES) cells. Hydrostatic pressures of 15, 30, 60, and 90 MPa were applied for 10 min, and changes in gene expression were evaluated. Among genes related to mechanical stimuli, death-associated protein 3 was upregulated in MEF subjected to 90 MPa pressure; however, other genes known to be upregulated by mechanical stimuli did not change significantly. Genes related to cell differentiation did not show a large change in expression. On the other hand, genes related to pluripotency, such as Oct4 and Sox2, showed a twofold increase in expression upon application of 60 MPa hydrostatic pressure for 10 min. Although these changes did not persist after overnight culture, cells that were pressurized to 15 MPa showed an increase in pluripotency genes after overnight culture. When mouse ES cells were pressurized, they also showed an increase in the expression of pluripotency genes. These results show that hydrostatic pressure activates pluripotency genes in mammalian cells.

This article has an associated First Person interview with the first author of the paper.

Summary: Application of high hydrostatic pressure on somatic cells induce changes in gene expression including upregulation in pluripotency genes.

Research and application of hydrostatic high pressure in tumor vaccines (Review)

It is well known that hydrostatic pressure (HP) is a physical parameter that is now regarded as an important variable for life. High hydrostatic pressure (HHP) technology has influenced biological systems for more than 100 years. Food and bioscience researchers have shown great interest in HHP technology over the past few decades. The development of knowledge related to this area can better facilitate the application of HHP in the life sciences. Furthermore, new applications for HHP may come from these current studies, particularly in tumor vaccines. Currently, cancer recurrence and metastasis continue to pose a serious threat to human health. The limited efficacy of conventional treatments has led to the need for breakthroughs in immunotherapy and other related areas. Research into tumor vaccines is providing new insights for cancer treatment. The purpose of this review is to present the main findings reported thus far in the relevant scientific literature, focusing on knowledge related to HHP technology and tumor vaccines, and to demonstrate the potential of applying HHP technology to tumor vaccine development.

Evaluation of alginate modification effect on cell-matrix interaction, mechanotransduction and chondrogenesis of encapsulated MSCs

Mesenchymal stem cells (MSCs) are promising cell candidates for cartilage regeneration. Furthermore, it is important to control the cell-matrix interactions that have a direct influence on cell functions. Providing an appropriate microenvironment for cell differentiation in response to exogenous stimuli is a critical step towards the clinical utilization of MSCs. In this study, hydrogels consisted of different proportions of alginates that were modified using gelatin, collagen type I and arginine-glycine-aspartic acid (RGD) and were evaluated regarding their effects on mesenchymal stem cells. The effect of applying hydrostatic pressure on MSCs encapsulated in collagen-modified alginate with and without chondrogenic medium was evaluated 7, 14 and 21 days after culture, which is a comprehensive evaluation of chondrogenesis in 3D hydrogels with mechanical and chemical stimulants. Alcian blue, safranin O and dimethyl methylene blue (DMMB) staining showed the chondrogenic phenotype of cells seeded in the collagen- and RGD-modified alginate hydrogels with the highest intensity after 21 days of culture. The results of real-time PCR for cartilage-specific extracellular matrix genes indicated the chondrogenic differentiation of MSCs in all hydrogels. Also, the synergic effects of chemical and mechanical stimuli are indicated. The highest expression levels of the studied genes were observed in the cells embedded in collagen-modified alginate by loading after 14 days of exposure to the chondrogenic medium. The effect of using IHP on encapsulated MSCs in modified alginate with collagen type I is equal or even higher than using TGF-beta on encapsulated cells. The results of immunohistochemical assessments also confirmed the real-time PCR data.

High Pressure Stress Response: Involvement of NMDA Receptor Subtypes and Molecular Markers

Professional divers who are exposed to high pressure (HP) above 1.1 MPa suffer from high pressure neurological syndrome (HPNS), which is characterized by reversible CNS hyperexcitability and cognitive and motor deficits. HPNS remains the final major constraints on deep diving at HP. Prolonged and repetitive exposure to HP during deep sea saturation dives may result in permanent memory and motor impairment. Previous studies revealed that CNS hyperexcitability associated with HPNS is largely induced by N-methyl-D-aspartate receptors (NMDARs). NMDARs that contain the GluN2A subunit are the only ones that show a large (∼60%) current increase at He HP. NMDAR subtypes that contain other GluN2 members show minor decrease or no change of the current. Immunoprecipitation was used in order to test the hypothesis that current augmentation may result from inserting additional NMDARs into the membrane during the 20–25 min compression. The results indicated that there is no increase in surface expression of NMDARs in the oocyte membrane under HP conditions. In contrast, consistent increase in glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and β-actin was discovered. GAPDH and β-actin are cytosolic proteins which involve in various cellular control processes, increase of their expression suggests the presence of a general cellular stress response to HP. Understanding the precise hyperexcitation mechanism(s) of specific NMDAR subtypes and other possible neurotoxic processes during HP exposure could provide the key for eliminating the adverse, yet reversible, short-term effects of HPNS and hopefully the deleterious long-term ones.

VIP Regulates Morphology and F-Actin Distribution of Schlemm's Canal in a Chronic Intraocular Pressure Hypertension Model via the VPAC2 Receptor

Purpose

To investigate the roles of vasoactive intestinal peptides (VIPs) in regulating the morphology and F-actin distribution of Schlemm's canal (SC) of rat eyes.

Methods

Chronic intraocular pressure (IOP) hypertension models with episcleral venous cauterization (EVC) were treated with topical VIP or PG99-465 (vasoactive intestinal peptide receptors 2 [VPAC2] antagonist). IOPs were measured with Tono-Pen, and the SC parameters, including the cross-section area, circumference, and length, were statistically evaluated by hematoxylin-eosin and CD31 immunohistochemical staining. Immunofluorescence was performed to detect the distribution of F-actin in the SC. Moreover, the distribution of filamentous actin (F-actin) and globular actin (G-actin) in human umbilical vein endothelial cells (HUVECs) was studied under a pressure system by immunofluorescence and Western blotting.

Results

Increased expressions of VIP and VPAC2 receptors, as well as a disordered distribution of F-actin were found in SC endothelial cells (SCEs) in the EVC model. Moreover, topical VIP maintained the normal distribution of F-actin in SCEs, expanded the collapsed SC, and induced a significant decrease in IOP in the EVC model. In in vitro HUVECs, the F-actin/G-actin ratio increased significantly under stress stimulation for 30 minutes. A total of 50 μM VIP helped maintain the normal F-actin/G-actin ratio of HUVECs against stress stimulation.

Conclusions

VIP regulates the distribution of F-actin in SCEs via the VPAC2 receptor in order to induce a decrease in IOP. VIP may represent a new target for antiglaucoma drugs.

On the Origin of Microtubules' High-Pressure Sensitivity

For over 50 years, it has been known that the mitosis of eukaryotic cells is inhibited already at high hydrostatic pressure conditions of 30 MPa. This effect has been attributed to the disorganization of microtubules, the main component of the spindle apparatus. However, the structural details of the depolymerization and the origin of the pressure sensitivity have remained elusive. It has also been a puzzle how complex organisms could still successfully inhabit extreme high-pressure environments such as those encountered in the depth of oceans. We studied the pressure stability of microtubules at different structural levels and for distinct dynamic states using high-pressure Fourier-transform infrared spectroscopy and Synchrotron small-angle x-ray scattering. We show that microtubules are hardly stable under abyssal conditions, where pressures up to 100 MPa are reached. This high-pressure sensitivity can be mainly attributed to the internal voids and packing defects in the microtubules. In particular, we show that lateral and longitudinal contacts feature different pressure stabilities, and they define also the pressure stability of tubulin bundles. The intactness of both contact types is necessary for the functionality of microtubules in vivo. Despite being known to dynamically stabilize microtubules and prevent their depolymerization, we found that the anti-cancer drug taxol and the accessory protein MAP2c decrease the pressure stability of microtubule protofilaments. Moreover, we demonstrate that the cellular environment itself is a crowded place and accessory proteins can increase the pressure stability of microtubules and accelerate their otherwise highly pressure-sensitive de novo formation.

Transient window of resilience during early development minimizes teratogenic effects of heat in zebrafish embryos

Background: Transient heat shock during early development is an established experimental paradigm for doubling the genome of the zebrafish zygote, which has practical applications in expedited identification of recessive mutations in genetic screens. Despite the simplicity of the strategy and the genetic tractability of zebrafish, heat shock has not been used for genome doubling since the proof‐of‐principle experiments done in the 1980s. This is because of poor survival of embryos that ensue from transient heat shocks and gross developmental abnormalities in the few survivors, which is incompatible with phenotype driven screens. Results: We show that heat shocks during early zebrafish development uncouple the second cycle of DNA and centrosome duplication. Interestingly, the developmental time of the heat shock that triggers the dissociation between DNA and centrosome duplication cycles significantly affect the potential of embryos to survive and attain normal morphology. The potential to develop normally after a heat shock alters in a developmental time span of 2 min in zebrafish embryos, a phenomenon that has not been reported in any species. Conclusions: The existence of heat resilient developmental windows and reduced heat teratogenicity during these windows could be an effective step forward in practical application of transient heat for experimental manipulation of ploidy in zebrafish. More broadly, heat resilience before zygotic genome activation suggests that metazoan embryos may possess innate protective features against heat beyond the canonical heat shock response. Developmental Dynamics 247:992–1004, 2018. © 2018 Wiley Periodicals, Inc.

Zebrafish embryos at the end of pronuclear fusion and before initiation of zygotic mitosis are resistant to teratogenic effects of heat.

The teratogenic heat resilient window exists transiently during the maternally controlled phase of development.

Heat shock during the teratogenic heat resilient window enables generation of morphologically normal zebrafish tetraploids.

Diploidization of haploids by transient heat shocks during the teratogenic heat resilient windows aids in effective generation of gynogenic diploids.

De novo transcriptome assembly and positive selection analysis of an individual deep-sea fish

Background

High hydrostatic pressure and low temperatures make the deep sea a harsh environment for life forms. Actin organization and microtubules assembly, which are essential for intracellular transport and cell motility, can be disrupted by high hydrostatic pressure. High hydrostatic pressure can also damage DNA. Nucleic acids exposed to low temperatures can form secondary structures that hinder genetic information processing. To study how deep-sea creatures adapt to such a hostile environment, one of the most straightforward ways is to sequence and compare their genes with those of their shallow-water relatives.

Results

We captured an individual of the fish species Aldrovandia affinis, which is a typical deep-sea inhabitant, from the Okinawa Trough at a depth of 1550 m using a remotely operated vehicle (ROV). We sequenced its transcriptome and analyzed its molecular adaptation. We obtained 27,633 protein coding sequences using an Illumina platform and compared them with those of several shallow-water fish species. Analysis of 4918 single-copy orthologs identified 138 positively selected genes in A. affinis, including genes involved in microtubule regulation. Particularly, functional domains related to cold shock as well as DNA repair are exposed to positive selection pressure in both deep-sea fish and hadal amphipod.

Conclusions

Overall, we have identified a set of positively selected genes related to cytoskeleton structures, DNA repair and genetic information processing, which shed light on molecular adaptation to the deep sea. These results suggest that amino acid substitutions of these positively selected genes may contribute crucially to the adaptation of deep-sea animals. Additionally, we provide a high-quality transcriptome of a deep-sea fish for future deep-sea studies.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4720-z) contains supplementary material, which is available to authorized users.

High hydrostatic pressure in cancer immunotherapy and biomedicine

High hydrostatic pressure (HHP) has been known to affect biological systems for >100 years. In this review, we describe the technology of HHP and its effect macromolecules and physiology of eukaryotic cells. We discuss the use of HHP in cancer immunotherapy to kill tumor cells for generation of whole cell and dendritic cell-based vaccines. We further summarize the current use and perspectives of HHP application in biomedicine, specifically in orthopedic surgery and for the viral, microbial and protozoan inactivation to develop vaccines against infectious diseases.

Exploring the stability limits of actin and its suprastructures

Actin is the main component of the microfilament system in eukaryotic cells and can be found in distinct morphological states. Global (G)-actin is able to assemble into highly organized, supramolecular cellular structures known as filamentous (F)-actin and bundled (B)-actin. To evaluate the structure and stability of G-, F-, and B-actin over a wide range of temperatures and pressures, we used Fourier transform infrared spectroscopy in combination with differential scanning and pressure perturbation calorimetry, small-angle x-ray scattering, laser confocal scanning microscopy, and transmission electron microscopy. Our analysis was designed to provide new (to our knowledge) insights into the stabilizing forces of actin self-assembly and to reveal the stability of the actin polymorphs, including in conditions encountered in extreme environments. In addition, we sought to explain the limited pressure stability of actin self-assembly observed in vivo. G-actin is not only the least temperature-stable but also the least pressure-stable actin species. Under abyssal conditions, where temperatures as low as 1-4°C and pressures up to 1 kbar are reached, G-actin is hardly stable. However, the supramolecular assemblies of actin are stable enough to withstand the extreme conditions usually encountered on Earth. Beyond ∼3-4 kbar, filamentous structures disassemble, and beyond ∼4 kbar, complete dissociation of F-actin structures is observed. Between ∼1 and 2 kbar, some disordering of actin assemblies commences, in agreement with in vivo observations. The limited pressure stability of the monomeric building block seems to be responsible for the suppression of actin assembly in the kbar pressure range.

Kinetic Insights into the Elongation Reaction of Actin Filaments as a Function of Temperature, Pressure, and Macromolecular Crowding

Actin polymerization is an essential process in eukaryotic cells that provides a driving force for motility and mechanical resistance for cell shape. By using preformed gelsolin-actin nuclei and applying stopped-flow methodology, we quantitatively studied the elongation kinetics of actin filaments as a function of temperature and pressure in the presence of synthetic and protein crowding agents. We show that the association of actin monomers to the pointed end of double-stranded helical actin filaments (F-actin) proceeds via a transition state that requires an activation energy of 56 kJ mol(-1) for conformational and hydration rearrangements, but exhibits a negligible activation volume, pointing to a compact transition state that is devoid of packing defects. Macromolecular crowding causes acceleration of the F-actin elongation rate and counteracts the deteriorating effect of pressure. The results shed new light on the combined effect of these parameters on the polymerization process of actin, and help us understand the temperature and pressure sensitivity of actin polymerization under extreme conditions.

Mechanosensitivity of the 2nd Kind: TGF-β Mechanism of Cell Sensing the Substrate Stiffness

Cells can sense forces applied to them, but also the stiffness of their environment. These are two different phenomena, and here we investigate the mechanosensitivity of the 2^nd kind: how the cell can measure an elastic modulus at a single point of adhesion—and how the cell can receive and interpret the chemical signal released from the sensor. Our model uses the example of large latent complex of TGF-β as a sensor. Stochastic theory gives the rate of breaking of latent complex, which initiates the signaling feedback loop after the active TGF-β release and leads to a change of cell phenotype driven by the α-smooth muscle actin. We investigate the dynamic and steady-state behaviors of the model, comparing them with experiments. In particular, we analyse the timescale of approach to the steady state, the stability of the non-linear dynamical system, and how the steady-state concentrations of the key markers vary depending on the elasticity of the substrate. We discover a crossover region for values of substrate elasticity closely corresponding to that of the fibroblast to myofibroblast transition. We suggest that the cell could actively vary the parameters of its dynamic feedback loop to ‘choose’ the position of the transition region and the range of substrate elasticity that it can detect. In this way, the theory offers the unifying mechanism for a variety of phenomena, such as the myofibroblast conversion in fibrosis of wounds and lungs and smooth muscle cell dysfunction in cardiac disease.

Combined effects of temperature, pressure, and co-solvents on the polymerization kinetics of actin

In vivo studies have shown that the cytoskeleton of cells is very sensitive to changes in temperature and pressure. In particular, actin filaments get depolymerized when pressure is increased up to several hundred bars, conditions that are easily encountered in the deep sea. We quantitatively evaluate the effects of temperature, pressure, and osmolytes on the kinetics of the polymerization reaction of actin by high-pressure stopped-flow experiments in combination with fluorescence detection and an integrative stochastic simulation of the polymerization process. We show that the compatible osmolyte trimethylamine-N-oxide is not only able to compensate for the strongly retarding effect of chaotropic agents, such as urea, on actin polymerization, it is also able to largely offset the deteriorating effect of pressure on actin polymerization, thereby allowing biological cells to better cope with extreme environmental conditions.

Mechanical regulation of mesenchymal stem cell differentiation

Biophysical cues play a key role in directing the lineage commitment of mesenchymal stem cells or multipotent stromal cells (MSCs), but the mechanotransductive mechanisms at play are still not fully understood. This review article first describes the roles of both substrate mechanics (e.g. stiffness and topography) and extrinsic mechanical cues (e.g. fluid flow, compression, hydrostatic pressure, tension) on the differentiation of MSCs. A specific focus is placed on the role of such factors in regulating the osteogenic, chondrogenic, myogenic and adipogenic differentiation of MSCs. Next, the article focuses on the cellular components, specifically integrins, ion channels, focal adhesions and the cytoskeleton, hypothesized to be involved in MSC mechanotransduction. This review aims to illustrate the strides that have been made in elucidating how MSCs sense and respond to their mechanical environment, and also to identify areas where further research is needed.

Explaining bathymetric diversity patterns in marine benthic invertebrates and demersal fishes: physiological contributions to adaptation of life at depth

Bathymetric biodiversity patterns of marine benthic invertebrates and demersal fishes have been identified in the extant fauna of the deep continental margins. Depth zonation is widespread and evident through a transition between shelf and slope fauna from the shelf break to 1000 m, and a transition between slope and abyssal fauna from 2000 to 3000 m; these transitions are characterised by high species turnover. A unimodal pattern of diversity with depth peaks between 1000 and 3000 m, despite the relatively low area represented by these depths. Zonation is thought to result from the colonisation of the deep sea by shallow-water organisms following multiple mass extinction events throughout the Phanerozoic. The effects of low temperature and high pressure act across hierarchical levels of biological organisation and appear sufficient to limit the distributions of such shallow-water species. Hydrostatic pressures of bathyal depths have consistently been identified experimentally as the maximum tolerated by shallow-water and upper bathyal benthic invertebrates at in situ temperatures, and adaptation appears required for passage to deeper water in both benthic invertebrates and demersal fishes. Together, this suggests that a hyperbaric and thermal physiological bottleneck at bathyal depths contributes to bathymetric zonation. The peak of the unimodal diversity-depth pattern typically occurs at these depths even though the area represented by these depths is relatively low. Although it is recognised that, over long evolutionary time scales, shallow-water diversity patterns are driven by speciation, little consideration has been given to the potential implications for species distribution patterns with depth. Molecular and morphological evidence indicates that cool bathyal waters are the primary site of adaptive radiation in the deep sea, and we hypothesise that bathymetric variation in speciation rates could drive the unimodal diversity-depth pattern over time. Thermal effects on metabolic-rate-dependent mutation and on generation times have been proposed to drive differences in speciation rates, which result in modern latitudinal biodiversity patterns over time. Clearly, this thermal mechanism alone cannot explain bathymetric patterns since temperature generally decreases with depth. We hypothesise that demonstrated physiological effects of high hydrostatic pressure and low temperature at bathyal depths, acting on shallow-water taxa invading the deep sea, may invoke a stress-evolution mechanism by increasing mutagenic activity in germ cells, by inactivating canalisation during embryonic or larval development, by releasing hidden variation or mutagenic activity, or by activating or releasing transposable elements in larvae or adults. In this scenario, increased variation at a physiological bottleneck at bathyal depths results in elevated speciation rate. Adaptation that increases tolerance to high hydrostatic pressure and low temperature allows colonisation of abyssal depths and reduces the stress-evolution response, consequently returning speciation of deeper taxa to the background rate. Over time this mechanism could contribute to the unimodal diversity-depth pattern.

Heuristic consequences of a load of oxygen in microtubules

The current cell oxygen paradigm shows some major gaps that have not yet been resolved. Something seems to be lacking for the comprehensive statement of the oxygen distribution in the cell, especially the low cytoplasmic oxygen level. The entrapment of oxygen in microtubules (MTs) resolves the latter observation, as well as the occurrence of an extensive cytoplasmic foam formation. It leads to a novel oxygen paradigm for cells. During the steady-state treadmilling, the mobile cavity would absorb oxygenated cytoplasm forward, entrap gas nuclei and concentrate them. A fluorescence method is described to confirm the in vitro load of oxygen in MTs during their periodic growths and shrinkages. The latter operating mechanism is called the gas dynamic instability (GDI) of MTs. Several known biosystems could rest on the GDI. (1) The GTP-cap is linked with the gas meniscus encountered in a tube filled with gas. The GTP hydrolysis is linked to the conformational change of the GTPase domain according to the bubble pressure, and to the shaking of protofilaments with gas particles (soliton-like waves). (2) The GDI provides a free energy water pump because water molecules have to escape from MT pores when foam concentrates within the MT. Beside ATP hydrolysis in motor proteins, the GDI provides an additional driving force in intracellular transport of cargo. The water streams flowing from the MT through slits organize themselves as water layers between the cargo and the MT surface, and break ionic bridges. It makes the cargo glide over a water rail. (3) The GDI provides a universal motor for chromosome segregation because the depolymerization of kinetochorial MTs is expected to generate a strong cytoplasmic foam. Chromosomes are sucked up according to the pressure difference (or density difference) applied to opposite sides of the kinetochore, which is in agreement with Archimedes' principle of buoyancy. Non-kinetochorial MTs reabsorb foam during GDI. Last, the mitotic spindle is imagined as a gas recycler. (4) The luminal particles within MTs (called MIPs) are imagined as a foam organizer, the luminal proteins being part of the borders and edges of identical bubbles. (5) Last, volatile anesthetics could destabilize MTs through anesthetic-induced bubble nucleation between protofilaments, and therefore causing shear stress and the opening of MT. The load of oxygen in MTs might provide a major advance in this area of research.

Determination of extremely high pressure tolerance of brine shrimp larvae by using a new pressure chamber system

Hydrostatic pressure is the only one of a range of environmental parameters (water temperature, salinity, light availability, and so on) that increases in proportion with depth. Pressure tolerance is therefore essential to understand the foundation of populations and current diversity of faunal compositions at various depths. In the present study, we used a newly developed pressure chamber system to examine changes in larval activity of the salt-lake crustacean, Artemia franciscana, in response to a range of hydrostatic pressures. We showed that A. franciscana larvae were able to survive for a short period at pressures of ≤ 60 MPa (approximately equal to the pressure of 6000 m deep). At a pressure of > 20 MPa, larval motor ability was suppressed, but not lost. Meanwhile, at a pressure of > 40 MPa, some of the larval motor ability was lost without recovery after decompression. For all experiments, discordance of movement and timing between right and left appendages, was observed at pressures of > 20 MPa. Our results indicate that the limit of pressure for sustaining active behavior of A. franciscana larvae is ∼20 MPa, whereas the limit of pressure for survival is within the range 30-60 MPa. Thus, members of the genus Artemia possess the ability to resist a higher range of pressures than their natural habitat depth. Our findings demonstrated an example of an organism capable of invading deeper environment in terms of physical pressure tolerance, and indicate the need and importance of pressure study as an experimental method.

Genes required for growth at high hydrostatic pressure in Escherichia coli K-12 identified by genome-wide screening

Despite the fact that much of the global microbial biosphere is believed to exist in high pressure environments, the effects of hydrostatic pressure on microbial physiology remain poorly understood. We use a genome-wide screening approach, combined with a novel high-throughput high-pressure cell culture method, to investigate the effects of hydrostatic pressure on microbial physiology in vivo. The Keio collection of single-gene deletion mutants in Escherichia coli K-12 was screened for growth at a range of pressures from 0.1 MPa to 60 MPa. This led to the identification of 6 genes, rodZ, holC, priA, dnaT, dedD and tatC, whose products were required for growth at 30 MPa and a further 3 genes, tolB, rffT and iscS, whose products were required for growth at 40 MPa. Our results support the view that the effects of pressure on cell physiology are pleiotropic, with DNA replication, cell division, the cytoskeleton and cell envelope physiology all being potential failure points for cell physiology during growth at elevated pressure.

EFFECTS OF HIGH PRESSURE IN THE ARMORED DINOFLAGELLATE SCRIPPSIELLA HEXAPRAECINGULA (PERIDINIALES, DINOPHYCEAE): CHANGES IN THECAL PLATE PATTERN AND MICROTUBULE ASSEMBLY(1)

The possible role of cortical microtubules in dinoflagellates was studied using high-pressure treatments applied to nonmotile cells (just after ecdysis) of Scrippsiella hexapraecingula T. Horig. et Chihara. Whereas considerable disorganization of cortical microtubules was observed when cells were exposed to high-pressure treatments of 98 MPa or more for 5-15 min, they were mostly intact in cells exposed to a pressure of <98 MPa for 5 min. After nonmotile cells were exposed to high-pressure treatments sufficient to disorganize the cortical microtubules, they produced new motile cells with thecal plate patterns that differed considerably from the pattern known for this species. Increasing the intensity of high pressure applied to nonmotile cells resulted in an increase in the number of cells that exhibited disorganized cortical microtubules as well as a change in their thecal plate pattern, suggesting that high pressure disorganizes cortical microtubules leading to a change in the thecal plate pattern.

Phosphoproteome analysis during larval development and metamorphosis in the spionid polychaete Pseudopolydora vexillosa

Background

The metamorphosis of the spionid polychaete Pseudopolydora vexillosa includes spontaneous settlement onto soft-bottom habitats and morphogenesis that can be completed in a very short time. A previous study on the total changes to the proteome during the various developmental stages of P. vexillosa suggested that little or no de novo protein synthesis occurs during metamorphosis. In this study, we used multicolor fluorescence detection of proteins in 2-D gels for differential analysis of proteins and phosphoproteins to reveal the dynamics of post-translational modification proteins in this species. A combination of affinity chromatography, 2D-PAGE, and mass spectrometry was used to identify the phosphoproteins in pre-competent larvae, competent larvae, and newly metamorphosed juveniles.

Results

We reproducibly detected 210, 492, and 172 phosphoproteins in pre-competent larvae, competent larvae, and newly metamorphosed juveniles, respectively. The highest percentage of phosphorylation was observed during the competent larval stage. About 64 stage-specific phosphoprotein spots were detected in the competent stage, and 32 phosphoproteins were found to be significantly differentially expressed in the three stages. We identified 38 phosphoproteins, 10 of which were differentially expressed during metamorphosis. These phosphoproteins belonged to six categories of biological processes: (1) development, (2) cell differentiation and integrity, (3) transcription and translation, (4) metabolism, (5) protein-protein interaction and proteolysis, and (6) receptors and enzymes.

Conclusion

This is the first study to report changes in phosphoprotein expression patterns during the metamorphosis of the marine polychaete P. vexillosa. The higher degree of phosphorylation during the process of attaining competence to settle and metamorphose may be due to fast morphological transitions regulated by various mechanisms. Our data are consistent with previous studies showing a high percentage of phosphorylation during competency in the barnacle Balanus amphitrite and the bryozoan Bugula neritina. The identified phosphoproteins may play an important role during metamorphosis, and further studies on the location and functions of important proteins during metamorphosis are warranted.

Hydrostatic pressure sensation in cells: integration into the tensegrity model

Hydrostatic pressure (HP) is a mechanical stimulus that has received relatively little attention in the field of the cell biology of mechanotransduction. Generalized models, such as the tensegrity model, do not provide a detailed explanation of how HP might be detected. This is significant, because HP is an important mechanical stimulus, directing cell behaviour in a variety of tissues, including cartilage, bone, airways, and the vasculature. HP sensitivity may also be an important factor in certain clinical situations, as well as under unique environmental conditions such as microgravity. While downstream cellular effects have been well characterized, the initial HP sensation mechanism remains unclear. In vitro evidence shows that HP affects cytoskeletal polymerization, an effect that may be crucial in triggering the cellular response. The balance between free monomers and cytoskeletal polymers is shifted by alterations in HP, which could initiate a cellular response by releasing and (or) activating cytoskeleton-associated proteins. This new model fits well with the basic tenets of the existing tensegrity model, including mechanisms in which cellular HP sensitivity could be tuned to accommodate variable levels of stress.

Piezotolerance of the cytoskeletal structure in cultured deep-sea fish cells using DNA transfection and protein introduction techniques

We used DNA transfection and protein introduction techniques to investigate the pressure tolerance of cytoskeletal structures in pectoral fin cells derived from the deep-sea fish Simenchelys parasiticus (habitat depth, 366-2,630 m). The deep-sea fish cells have G418 resistance. The cell number increased until day 6 of cultivation and all cells had died by day 35 when cultured in 35-mm Petri dishes in medium containing G418. Enhanced yellow fluorescent protein-tagged human beta-actin (EYFP-actin) was stably expressed by 1 in 100,000 deep-sea fish cells. Because almost none of the EYFP-actin was incorporated into actin filaments of the cells, we replaced the relatively large EYFP tag with a chemical fluorescent compound and succeeded in incorporating fluorescently labeled rabbit actins into the deep-sea fish actin filaments. Most of the filament structure in the cells with rabbit actin inserted underwent depolymerization when subjected to pressure of 100 MPa for 20 min, in contrast to control cells. There were no differences in the tubulin filament structure between control cells and deep-sea fish cells with fluorescein-labeled bovine tubulin inserted after the application of pressure ranging from 40 to 100 MPa for 20 min.

Characterization of dual-wavelength seminaphthofluorescein and seminapthorhodafluor dyes for pH sensing under high hydrostatic pressures

Hydrostatic pressure is an important physical parameter in biology, with pressures in the few-hundred-atm range having significant effects on cellular morphology, metabolism, and viability. To ensure valid results when studying pressure effects using fluorescence spectroscopy and imaging methods, metabolic probes need to be characterized for high-pressure use. Of interest is the sensing of pH at high pressures due to the key role that pH plays in cellular function. Despite the availability of pH-sensitive dyes, only a few have been characterized for high-pressure use. Here we present the effects of pressure on the acid-base equilibria of four dual-wavelength seminaphthorhodafluor and seminaphthofluorescein dyes (pK(a)=6.6-7.8). Using phosphate buffers as high-pressure pH references, we investigate the pressure dependence of pK(a) for these dyes and determine the volume change associated with the acid-dissociation reaction. We find that if pressure-induced pK(a) changes are not accounted for during interpretation of emission spectra, systematic errors of up to 0.02 pH units per 100atm would result, comparable to previously measured pressure-induced pH changes in vivo. Results are validated by correctly sensing pH changes in Tris and acetate solutions. Methods presented here are applicable to other metabolic probes utilizing dual-wavelength ratiometric sensing modes.

Micropatterning of living cells on a heterogeneously wetted surface

We report a simple approach to fabricate heterogeneously wetted surfaces which can be used to pattern living cells or biomolecules. An array of pedestals composed of SU-8 was fabricated on a glass surface which was then derivatized with a hydrophobic silane. Upon addition of aqueous solutions to the array, air was trapped within the hydrophobic cavities between the pedestals. The trapped air formed a "virtual wall" blocking access to these cavities. Cells cultured on the array were forced to grow only on the tops of the pedestals, i.e., the surfaces wetted by aqueous media. The virtual walls were stable during manipulation of the array and over long time periods (months).

Effects of the piezo-tolerance of cultured deep-sea eel cells on survival rates, cell proliferation, and cytoskeletal structures

We investigated the pressure tolerance of deep-sea eel (Simenchelys parasiticus; habitat depth, 366-2,630 m) cells, conger eel (Conger myriaster) cells, and mouse 3T3-L1 cells. Although there were no living mouse 3T3-L1 and conger eel cells after 130 MPa (0.1 MPa = 1 bar) hydrostatic pressurization for 20 min, all deep-sea eel cells remained alive after being subjected to pressures up to 150 MPa for 20 min. Pressurization at 40 MPa for 20 min induced disruption of actin and tubulin filaments with profound cell-shape changes in the mouse and conger eel cells. In the deep-sea eel cells, microtubules and some actin filaments were disrupted after being subjected to hydrostatic pressure of 100 MPa and greater for 20 min. Conger eel cells were sensitive to pressure and did not grow at 10 MPa. Mouse 3T3-L1 cells grew faster under pressure of 5 MPa than at atmospheric pressure and stopped growing at 18 MPa. Deep-sea eel cells were capable of growth in pressures up to 25 MPa and stopped growing at 30 MPa. Deep-sea eel cells required 4 h at 20 MPa to finish the M phase, which was approximately fourfold the time required under atmospheric conditions.

Influence of environmental conditions on early development of the hydrothermal vent polychaete Alvinella pompejana

Dispersal and colonisation processes at deep-sea vents are still not fully understood, essentially because early life stages of vent species remain unknown. The polychaete worm Alvinella pompejana forms colonies on chimney walls at East Pacific Rise vent sites where the temperature can frequently exceed 20°C. In vitro studies in pressure vessels showed that the early embryos tolerate temperatures in a lower range(10–14°C), suggesting that they would have to escape the colony to develop. Pressure vessels offer the advantage that each parameter can be independently controlled, but they do not simulate the more complex and dynamic conditions naturally encountered at vent sites. Accordingly, in addition to incubations in pressure vessels, we incubated embryos directly at a vent site, in different habitats along a gradient of hydrothermal influence. Embryos incubated on an adult A. pompejana colony where temperature and H2S concentrations were relatively high showed a very low survival rate and did not develop, whereas embryos incubated in a Riftia pachyptila clump environment with a lower hydrothermal signature, or at the base of the chimney where the influence of the hydrothermal activity was very weak, survived well and developed. Although the average temperature recorded in the A. pompejana colony was within the range tolerated by embryos (13°C), frequent peaks above 20°C were recorded. Estimated sulphide concentration at this site reached 200 μmol l–1. Punctuated exposure to both high temperature and elevated sulphide levels probably explain the low survival of embryos within the A. pompejanacolony. The in situ experiments further support the idea that embryos require conditions with moderate hydrothermal influence not generally found within an adult colony. However, as much more benign physicochemical conditions can be found within a few tens of cm of adult colonies, embryos do not necessarily have to leave their vent of origin to develop. Further analyses are needed to pinpoint the specific factors that affect the survival and development of embryos at vents.

Effects of high hydrostatic pressure on bacterial cytoskeleton FtsZ polymers in vivo and in vitro

Some rod-shaped bacteria, including Escherichia coli, exhibit cell filamentation without septum formation under high-hydrostatic-pressure conditions, indicating that the cell-division process is affected by hydrostatic pressure. The effects of elevated pressure on FtsZ-ring formation in E. coli cells were examined using indirect immunofluorescence microscopy. Elevated pressure of 40 MPa completely inhibited colony formation of E. coli cells under the cultivation conditions used, and the cells exhibited obviously filamentous shapes. In the elongated cells, normal cell-division processes appeared to be inhibited, because no FtsZ rings were observed by indirect immunofluorescent staining. In addition, it was observed that hydrostatic pressure dissociated the E. coli FtsZ polymers in vitro. These results suggest that high hydrostatic pressure directly affects cell survival and morphology through the dissociation of the cytoskeletal frameworks.

Genomic expression pattern inSaccharomyces cerevisiaecells in response to high hydrostatic pressure

Gene expression patterns in response to hydrostatic pressure were determined by whole genome microarray hybridization. Functional classification of the 274 genes affected by pressure treatment of 200 MPa for 30 min revealed a stress response expression profile. The majority of the >2-fold upregulated genes were involved in stress defense and carbohydrate metabolism while most of the repressed ones were in cell cycle progression and protein synthesis categories. Furthermore, uncharacterized genes were among the 10 highest expressed sequences and represented 45% of the total upregulated genes. The results of this study revealed a hydrostatic pressure-specific stress response pattern and suggested interesting information about the mechanisms involved in adaptation of cells to a high-pressure environment.

Noninvasive cardiac absolute pressure sensing: a fundamentally new approach

Noninvasive cardiac pressure sensing using an imaging modality to ascertain changes in absolute pressure would be of immense benefit as a replacement for the Swan-Ganz catheter in current use. However, very little research has been published in this area. This paper reviews the small number of relevant studies to date, points out the many gaps in the research record, and discusses possible new avenues of approach in solving the problem.

Structural and functional effects of hydrostatic pressure on centrosomes from vertebrate cells

In an attempt to better understand the role of centrioles in vertebrate centrosomes, hydrostatic pressure was applied to isolated centrosomes as a means to disassemble centriole microtubules. Treatments of the centrosomes were monitored by analyzing their protein composition, ultrastructure, their ability to nucleate microtubules from pure tubulin, and their capability to induce parthenogenetic development of Xenopus eggs. Moderate hydrostatic pressure (95 MPa) already affected the organization of centriole microtubules in isolated centrosomes, and also impaired microtubule nucleation. At higher pressure, the protein composition of the peri-centriolar matrix (PCM) was also altered and the capacity to nucleate microtubules severely impaired. Incubation of the treated centrosomes in Xenopus egg extract could restore their capacity to nucleate microtubules after treatment at 95 MPa, but not after higher pressure treatment. However, the centriole structure was in no case restored. It is noteworthy that centrosomes treated with mild pressure did not allow parthenogenetic development after injection into Xenopus eggs, even if they had recovered their capacity to nucleate microtubules. This suggested that, in agreement with previous results, centrosomes in which centriole architecture is impaired, could not direct the biogenesis of new centrioles in Xenopus eggs. Centriole structure could also be affected by applying mild hydrostatic pressure directly to living cells. Comparison of the effect of hydrostatic pressure on cells at the G1/S border or on the corresponding cytoplasts suggests that pro-centrioles are very sensitive to pressure. However, cells can regrow a centriole after pressure-induced disassembly. In that case, centrosomes eventually recover an apparently normal duplication cycle although with some delay.

Effects of high hydrostatic pressures on living cells: a consequence of the properties of macromolecules and macromolecule-associated water

Sixty percent of the Earth's biomass is found in the sea, at depths greater than 1000 m, i.e., at hydrostatic pressures higher than 100 atm. Still more surprising is the fact that living cells can reversibly withstand pressure shifts of 1000 atm. One explanation lies in the properties of cellular water. Water forms a very thin film around macromolecules, with a heterogeneous structure that is an image of the heterogeneity of the macromolecular surface. The density of water in contact with macromolecules reflects the physical properties of their different domains. Therefore, any macromolecular shape variations involving the reorganization of water and concomitant density changes are sensitive to pressure (Le Chatelier's principle). Most of the pressure-induced changes to macromolecules are reversible up to 2000 atm. Both the effects of pressure shifts on living cells and the characteristics of pressure-adapted species are opening new perspectives on fundamental problems such as regulation and adaptation.

Effects of hydrostatic pressure on the Leptospira interrogans: high immunogenicity of the pressure-inactivated serovar hardjo

The Hardjoprajitno strain of Leptospira interrogans serovar hardjo was subjected to different hydrostatic pressures. Complete inactivation occurred when the leptospires were treated with 2 kbar for 60 min. Electron microscopy showed dislocation of the outer membrane, partial loss of the helical shape and extrusion of the axial filament from the cytoplasmic cylinder of the pressurized leptospires. When the pressure-treated leptospires were inoculated into rabbits they were highly immunogenic. The sera of these animals presented a titer of 2048 in the microscopic serum agglutination reaction. Fluorescence measurements indicated that the action of pressure on the leptospires might have resulted from perturbation on membrane protein components, permitting the binding of the fluorescent probe bis (8-anilinonaphthalene-1-sulfonate) (Bis-ANS). This is the first report of the use of hydrostatic pressure to inactivate pathogenic bacteria with the potential to lead to a vaccine.

Effect of hydrostatic pressure on the morphology and ultrastructure of wild-type and trehalose synthase mutant cells of Saccharomyces cerevisiae

AIMS

Saccharomyces cerevisiae was used for studying the physiological effects of hydrostatic pressure.

METHODS AND RESULTS

The effects of hydrostatic pressure on the ultrastructure of wild-type and trehalose-6-phosphate synthase (tps1) mutant cells were investigated by transmission electron microscopy. Pressure induced several morphological changes in wild-type and tps1 cells, the latter showing greater structural alterations. When the cells were submitted to a preheat treatment they both acquired resistance to the pressure treatment.

CONCLUSION

As the tps1 mutant was 1000-fold more barosensitive than its parental strain, it showed greater structural alterations compared with the wild-type. Microscopic images of the yeast cells suggested that hydrostatic pressure induced changes in the cytoskeleton and therefore, on the cell wall and in the dynamics of the organelles.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work presents the effects of hydrostatic pressure on the morphology of yeast cells and confirms the importance of several different factors in the protection of cells against stress.

Primary chondrocytes resist hydrostatic pressure-induced stress while primary synovial cells and fibroblasts show modified Hsp70 response

OBJECTIVE

During joint loading, chondrocytes in the articular cartilage are subjected to gradients of high compressive hydrostatic pressure (HP). In response to diverse chemical or physical stresses, heat shock genes are induced to express heat shock proteins (Hsps). This study sought to examine the role of Hsps in baroresistance in primary bovine chondrocytes and synovial cells, as well as in primary human fibroblasts.

METHODS

Northern blotting was used to analyze the steady-state levels of hsp70 mRNA in the primary cells exposed to HP or heat stress. Hsp70 protein accumulation was analyzed by Western blotting, and the DNA-binding activity was examined by gel mobility shift assay.

RESULTS

Primary bovine chondrocytes which have been adapted to live under pressurized conditions showed negligible Hsp70 response upon HP loading, whereas primary bovine synovial cells and human fibroblasts accumulated hsp70 mRNA and protein when subjected to HP. The response was initiated without activation of the heat shock transcription factor 1. Interestingly, pre-conditioning of the barosensitive fibroblasts with HP or heat shock reduced the Hsp70 response, indicating induction of baroresistance.

CONCLUSION

This study suggests that Hsp70 can play an important role in the early stages of adaptation of cells to HP. Thus, the Hsp70 gene expression upon HP loading may serve as one indicator of the chondrocytic phenotype of the cells. This can be of use in the treatment of cartilage lesions.

Hydrostatic pressure shows that lamellipodial motility in Ascaris sperm requires membrane-associated major sperm protein filament nucleation and elongation

Sperm from nematodes use a major sperm protein (MSP) cytoskeleton in place of an actin cytoskeleton to drive their ameboid locomotion. Motility is coupled to the assembly of MSP fibers near the leading edge of the pseudopod plasma membrane. This unique motility system has been reconstituted in vitro in cell-free extracts of sperm from Ascaris suum: inside-out vesicles derived from the plasma membrane trigger assembly of meshworks of MSP filaments, called fibers, that push the vesicle forward as they grow (Italiano, J.E., Jr., T.M. Roberts, M. Stewart, and C.A. Fontana. 1996. Cell. 84:105-114). We used changes in hydrostatic pressure within a microscope optical chamber to investigate the mechanism of assembly of the motile apparatus. The effects of pressure on the MSP cytoskeleton in vivo and in vitro were similar: pressures >50 atm slowed and >300 atm stopped fiber growth. We focused on the in vitro system to show that filament assembly occurs in the immediate vicinity of the vesicle. At 300 atm, fibers were stable, but vesicles often detached from the ends of fibers. When the pressure was dropped, normal fiber growth occurred from detached vesicles but the ends of fibers without vesicles did not grow. Below 300 atm, pressure modulates both the number of filaments assembled at the vesicle (proportional to fiber optical density and filament nucleation rate), and their rate of assembly (proportional to the rates of fiber growth and filament elongation). Thus, fiber growth is not simply because of the addition of subunits onto the ends of existing filaments, but rather is regulated by pressure-sensitive factors at or near the vesicle surface. Once a filament is incorporated into a fiber, its rates of addition and loss of subunits are very slow and disassembly occurs by pathways distinct from assembly. The effects of pressure on fiber assembly are sensitive to dilution of the extract but largely independent of MSP concentration, indicating that a cytosolic component other than MSP is required for vesicle-association filament nucleation and elongation. Based on these data we present a model for the mechanism of locomotion-associated MSP polymerization the principles of which may apply generally to the way cells assemble filaments locally to drive protrusion of the leading edge.