Graviresponses of osteocytes under altered gravity

Single cell was capable of sensing and responding to alterations of gravity. Osteocytes, as the most abundant cells of the bone tissue playing an important role in the bone mechanotransduction, are very sensitive to mechanical stimuli. However, the effect of altered gravity on osteocytes so far is less known according to the public papers. Further study on this issue will help to verify and develop the theory of how cells perceive and respond to gravity. It also brings new ideas to the study of space bone loss. In our study, Osteocyte-like MLO-Y4 cells were exposed to 30 parabolic flights three times on ZERO-G airbus A300 to investigate the comprehensive effect on osteocytes stimulated by hyper- and hypo-gravity forces. It showed that the cell morphology, as well as cell area and height, was not changed significantly by hyper-gravity and hypo-gravity. However, the cytoskeleton was reorganized. In flight cells, F-actin polymerization was enhanced at the cell periphery and microtubule organizing center disappeared, but no apoptotic feathers were detected. The results of western blot showed that connexin 43 (Cx43) expression was down-regulated, indicating an decrease of gap-junction. In conclusion, hyper- and hypo-gravity stimulation altered the cytoskeleton architecture and suppressed gap-junction of osteocyte-like MLO-Y4 cells.     

Gravisensing in plants and fungi.

The principle of establishing and maintaining a gravitropic set point angle depends on gravisensing and a subsequent cascade of events that result in differential elongation of the responsive structures. Since gravity acts upon masses, the gravisensing mechanisms of all biological systems must follow the same principle, namely the sensing of some force due to differential acceleration of the perceiving entity and a reference structure. This presentation will demonstrate that gravisensing can be accomplished by various means, ranging from cytoskeletal organization, mechano-elastic stress to perturbation of electric signals. However, several arguments indicate that sedimentation of either dense plastids (statoliths), the entire protoplast, or a combination of these represents the primary step in graviperception in plants. In fungi, nuclei and cytoskeletal proteins are believed to form a network capable of gravisensing but sedimenting organelles that may function as statoliths have been identified. Theoretical and practical limitations of gravisensing and detection of acceleration forces necessitate microgravity experiments to identify the primary perceptor, subsequent biochemical mechano-transduction, and biological response processes.     

Fullerenes in space.

The discovery and synthesis of fullerenes led to the hypothesis that they may be present and stable in interstellar space. Fullerenes have been reported in an impact crater on the LDEF spacecraft. Investigations of fullerenes in carbonaceous meteorites have yielded only small upper limits. Fullerene compounds and their ions could be interesting carrier molecules for some of the "diffuse interstellar bands" (DIBs), a long standing mystery in astronomy. We have detected two new diffuse bands that are consistent with laboratory measurements of the C60+, as first evidence for the largest molecule ever detected in space. Criteria for this identification are discussed. The inferred abundance (up to 0.9 % of cosmic carbon locked in C60+) suggests that fullerenes may play an important role in interstellar chemistry. We present new observations on DIB substructures consistent with fullerene compounds, and the search for neutral C60 in the diffuse medium.     

Gravisensing in roots.

The mode of gravisensing in higher plants is not yet elucidated. Although, it is generally accepted that the amyloplasts (statoliths) in the root cap cells (statocytes) are responsible for susception of gravity. However, the hypothesis that the whole protoplast acts as gravisusceptor cannot be dismissed. The nature of the sensor that is able to transduce and amplify the mechanical energy into a biochemical factor is even more controversial. Several cell structures could potentially serve as gravireceptors: the endoplasmic reticulum, the actin network, the plasma membrane, or the cytoskeleton associated with this membrane. The nature of the gravisusceptors and gravisensors is discussed by taking into account the characteristics of the gravitropic reaction with respect to the presentation time, the threshold acceleration, the reciprocity rule, the deviation from the sine rule, the movement of the amyloplasts, the pre-inversion effect, the response of starch free and intermediate mutants and the effects of cytochalasin treatment. From this analysis, it can be concluded that both the amyloplasts and the protoplast could be the gravisusceptors, the former being more efficient than the latter since they can focus pressure on limited areas. The receptor should be located in the plasma membrane and could be a stretch-activated ion channel.     

Gravitaxis in unicellular microorganisms.

Orientation of organisms with respect to the gravitational field of the Earth has been studied for more than 100 years in a number of unicellular microorganisms including flagellates and ciliates. Several hypotheses have been developed how the weak stimulus is perceived. Intracellular statoliths have been found to be involved in gravitaxis of Loxodes, while no specialized organelles have been detected in other ciliates, e.g. Paramecium. Also in the slime mold Physarum no specialized gravireceptors have been identified yet. In the flagellate Euglena gracilis the whole cell body, which is denser than the surrounding medium, seems to act as a statolith pressing onto the lower membrane where it activates mechanosensitive ion channels. Similar results were obtained for the ciliate Paramecium. In contrast to the flagellate Euglena, several ciliates have been found to show gravikinesis, which is defined as a dependence of the swimming velocity on the direction of movement in the gravity field.     

Liposome formation in microgravity.

Liposomes are artificial vesicles with a phospholipid bilayer membrane. The formation of liposomes is a self-assembly process that is driven by the amphipathic nature of phospholipid molecules and can be observed during the removal of detergent from phospholipids dissolved in detergent micelles. As detergent concentration in the mixed micelles decreases, the non-polar tail regions of phospholipids produce a hydrophobic effect that drives the micelles to fuse and form planar bilayers in which phospholipids orient with tail regions to the center of the bilayer and polar head regions to the external surface. Remaining detergent molecules shield exposed edges of the bilayer sheet from the aqueous environment. Further removal of detergent leads to intramembrane folding and membrane folding and membrane vesiculation, forming liposomes. We have observed that the formation of liposomes is altered in microgravity. Liposomes that were formed at 1-g did not exceed 150 nm in diameter, whereas liposomes that were formed during spaceflight exhibited diameters up to 2000 nm. Using detergent-stabilized planar bilayers, we determined that the stage of liposome formation most influenced by gravity is membrane vesiculation. In addition, we found that small, equipment-induced fluid disturbances increased vesiculation and negated the size-enhancing effects of microgravity. However, these small disturbances had no effect on liposome size at 1-g, likely due to the presence of gravity-induced buoyancy-driven fluid flows (e.g., convection currents). Our results indicate that fluid disturbances, induced by gravity, influence the vesiculation of membranes and limit the diameter of forming liposomes.     

Pituitary cells in space.

Cells of the mammalian pituitary gland synthesize and secrete several protein hormones which regulate a number of organ systems throughout the body. These include the musculoskeletal, immune, vascular and endocrine systems. Since changes occur in these tissues as a result of spaceflight, and since pituitary growth hormone (GH) and prolactin (PRL) play a role in the control of these systems on earth, we have focused attention over the last 10 years on GH and PRL cell function during and after spaceflight. The cumulative results of 4 spaceflight missions and several mimicked microgravity experiments establish 1) that production and release of biologically active GH and PRL is repeatedly and significantly attenuated (usually > 50%) and 2) that changes in cell morphology also occur. In this paper we describe our results within the framework of methodologies and approaches frequently used to study pituitary cell function on earth. In so doing we hope to develop future flight experiments aimed at uncovering possible microgravity "sensing systems" within the pituitary cell.     

Progress in plant research in space.

Progress is reviewed of spaceflight research conducted with plants between 1987 and 1992. Numerous plant experiments have been performed on spacecraft and sounding rockets in the past five years by scientists of the US, the former Soviet Union, Europe, and other areas. The experiments are categorized into three areas: gravity sensing, transduction, and response; development and reproduction; and metabolism, photosynthesis, and transport. The results of these experiments continue to demonstrate that gravity and/or other factors of spaceflight affect plants at the organismal, cellular, subcellular, and molecular levels, resulting in changes in orientation, development, metabolism, and growth. The challenge now is to truly dissect the effects of gravity from those of other spaceflight factors and to identify the basic mechanisms underlying gravity's effects.     

Amino acids in meteorites.

Carbonaceous chondrites carry a record of chemical evolution that is unparalleled among presently accessible natural materials. Within the complex suite of organic compounds that characterize these meteorites, amino acids occur at a total concentration that may reach 0.6 micromole g-1 meteorite (approximately 60 ppm). Both free amino acids and acid-labile amino acid derivatives have been found in hot-water extracts of a CI1 and seven CM2 chondrites. Although the amino acid composition of all CM2 chondrites is not the same, differences may be largely explicable on the basis of spontaneous and biologically-caused decomposition occurring during their terrestrial residence. The amino acids of the Murchison meteorite (CM2) have been extensively analyzed and 52 amino acids have been positively identified. Thirty three of these amino acids are unknown in natural materials other than carbonaceous chondrites. Thus the Murchison meteorite has recently been the major source of new naturally-occurring amino acids. The Murchison amino acids comprise a mixture of C2 through C8 cyclic and acyclic monoamino alkanoic and alkandioic acids of nearly complete structural diversity. Within the acyclic monoamino alkanoic acid series, primary alpha-amino alpha-branched amino acids are predominant. The concentrations of individual amino acids decline exponentially with increasing carbon number within homologous series. Amino acid enantiomers are found in approximately equal amounts. Eight of the terrestrial protein amino acids have been found.     

Complex organics in meteorites.

Complex macromolecular organic matter is present in carbonaceous chondrites as the most abundant organic matter and may be present in interstellar dusts and comets. With this view, our studies of the complex organic matter isolated from six CM2 chondrites, namely Yamato-74662, Yamato-791198, Yamato-793321, Yamato-86720, Belgica-7904, and Murchison are introduced and discussed in the text. The complex organic matter is acid-insoluble and organic solvent-insoluble, and therefore, it was examined by heating experiments to obtain information on its chemical constituents and characteristics. Three chondrites, Yamato-74662, Yamato-791198, and Murchison which have solvent-extractable organic compounds, such as amino acids, carboxylic acid, hydrocarbons, etc. possess thermally labile organic fraction in the complex organic matter. Organic compounds detected in the pyrolyzate of the complex organic matter number over 130 of which aromatic hydrocarbons are dominant. They appeared around 300 degrees C, and disappeared at about 600 degrees C with a maximum at 400-500 degrees C during the heating. On the other hand, the other three chondrites do not have the extractable organic compounds nor a thermally labile organic fraction. The presence or absence of the fraction in the complex organic matter likely indicates the presence or absence of the solvent-extractable organic compounds and relates to thermal history of the chondrite.     

从天而降 美国敏捷全球打击计划进行时

新闻链接2010年12月8日,空军太空项目副部长理查德·麦金尼称,第二架X-37B将在2011年3月～4月之间由"宇宙神"5火箭发射。这次X-37B轨道试验飞行器(OTV)任务将"扩展运行包线",以试验横向飞行范围的回收特性,并在更极端的天气条件下尝试回收。     

Ultrastructural changes in osteocytes in microgravity conditions.

We examined the histology and morphometry of biosamples (biopsies) of the iliac crest of monkeys, flown 14 days aboard the "Bion-11", using electron microscopy. We found, that some young osteocytes take part in the activation of collagen protein biosynthesis in the adaptive remodeling process of the bone tissue to microgravity conditions. Osteocyte lacunae filled with collagen fibrils; this correlates with fibrotic osteoblast reorganization in such zones. The osteolytic activity in mature osteocytes is intensified. As a result of osteocyte destruction, the quantity of empty osteocytic lacunae in the bone tissue increases.     

Mammalian cell cultivation in space.

Equipment used in space for the cultivation of mammalian cells does not meet the usual standard of earth bound bioreactors. Thus, the development of a space worthy bioreactor is mandatory for two reasons: First, to investigate the effect on single cells of the space environment in general and microgravity conditions in particular, and second, to provide researchers on long term missions and the Space Station with cell material. However, expertise for this venture is not at hand. A small and simple device for animal cell culture experiments aboard Spacelab (Dynamic Cell Culture System; DCCS) was developed. It provides 2 cell culture chambers, one is operated as a batch system, the other one as a perfusion system. The cell chambers have a volume of 200 microliters. Medium exchange is achieved with an automatic osmotic pump. The system is neither mechanically stirred nor equipped with sensors. Oxygen for cell growth is provided by a gas chamber that is adjacent to the cell chambers. The oxygen gradient produced by the growing cells serves to maintain the oxygen influx by diffusion. Hamster kidney cells growing on microcarriers were used to test the biological performance of the DCCS. On ground tests suggest that this system is feasible.     

Graviperception and gravitaxis in algae.

Photosynthetic flagellates are among the most intensely studied unicellular organisms in the field of graviperception and gravitaxis. While the phenomenon of graviorientation has been known for many decades, only recently was the molecular mechanism unveiled. Earlier hypotheses tried to explain the precise orientation by a passive buoy mechanism assuming the tail end to be heavier than the front. In the photosynthetic flagellate Euglena gracilis, the whole cell body is denser than the surrounding medium, pressing onto the lower cell membrane where it seems to activate mechanosensitive ion channels specific for calcium. The calcium entering the cells during reorientation can be visualized by the fluorescence probe, Calcium Crimson. Cyclic AMP is likewise involved in the molecular pathway. Inhibitors of calcium channels and ionophores impair gravitaxis while caffeine, a blocker of the phosphodiesterase, enhances the precision of orientation.     

Progress in European CELSS activities.

The European CELSS activities started in the late 1970's with system analysis and feasibility studies of Biological Life Support Systems (BLSS). Since then the European efforts have continued in two major directions: as a series of individual development tasks like the Environmental Life Support System and the Solar Plant Growth Facility, and in parallel hereto as overall coordination and planning activities for life support system long term needs definition and payload definition for COLUMBUS utilization. The early initiations for CELSS came from the industry side in Europe, but since then planning and hardware feasibility analyses have been initiated also from customer/agency side. Despite this, it is still to early to state that a "CELSS-programme" as a "concerted" effort has been agreed upon in Europe. However, the general CELSS objectives have been accepted as planning and possible development goals for the European effort for manned space activities, and as experimental planning topics in the life sciences community for the next decades.     

Isotopic ratios in planetary atmospheres.

Recent progress on measurements of isotopic ratios in planetary or satellite atmospheres include measurements of the D/H ratio in the methane of Uranus, Neptune and Titan and in the water of Mars and Venus. Implications of these measurements on our understanding of the formation and evolution of the planets and satellite are discussed. Our current knowledge of the carbon, nitrogen and oxygen isotopic ratios in the atmospheres of these planets, as well as on Jupiter and Saturn, is also reviewed. We finally show what progress can be expected in the very near future due to some new ground-based instrumentation particularly well suited to such studies, and to forthcoming space missions.     

Gravity sensing in moss protonemata.

Moss protonemata are a valuable system for studying gravitropism because both sensing and upward curvature (oriented tip growth) take place in the same cell. We review existing evidence, especially for Ceratodon purpureus, that addresses whether the mass that functions in sensing is that of amyloplasts that sediment. Recent experiments show that gravitropism can take place in media that are denser than the apical cell. This indicates that gravity sensing relies on an intracellular mass rather than that of the entire cell and provides further support for the starch-statolith hypothesis of sensing. Possible mechanisms for how amyloplast mass functions in sensing and transduction are discussed.     

Confocal microscopy in microgravity research.

We have studied the application and the feasibility of confocal scanning laser microscopy (CSLM) in microgravity research. Its superior spatial resolution and 3D imaging capabilities and its use of light as a probe, render this instrument ideally suited for the study of living biological material on a (sub-)cellular level. In this paper a number of pertinent biological microgravity experiments is listed, concentrating on the direct observation of developing cells and cellular structures under microgravity condition. A conceptual instrument design is also presented, aimed at sounding rocket application followed by Biorack/Biolab application at a later stage.     

Space radiobiology program in Russia.

The space radiobiology program in Russia is aimed at obtaining fundamental data for developing radiation safety criteria. These criteria are necessary for long-term space missions. This program includes : -substantiation of radiation hazard estimation principles based on the radiation risk conception, -investigation of the radiation affection regularities under the combined influence of the spaceflight factors, -experimental investigation of the HZE-particle delayed effects and acute somatic effects induced by protons and electrons, -individual radiosensitivity investigation, -mathematic modeling of radiobiological effects , -radiobiological basis of control and forecast of radiation influence in space, -development of methods and means of an organism's radioresistance increase.     

Virus protein assembly in microgravity.

The coat of polyomavirus is composed of three proteins that can self-assemble to form an icosahedral capsid. VP1 represents 75% of the virus capsid protein and the VP1 capsomere subunits are capable of self assembly to form a capsid-like structure. Ground-based and orbiter studies were conducted with VP1 protein cloned in an expression vector and purified to provide ample quantities for capsomere-capsid assembly. Flight studies were conducted on STS-37 on April 5-9, 1991. Assembly initiated when a VP1 protein solution was interfaced with a Ca+2 buffer solution (pH 5.0). After four days a second alignment terminated the assembly process and allowed for glutaraldehyde fixation. Flight and ground-based samples were analyzed by electron microscopy. Ground-based experiments revealed the assembly of VP1 into capsid-like structures and a heterogenous size array of capsomere subunits. Samples reacted in microgravity, however, showed capsomeres of a homogenous size, but lack of capsid-like assembly.