Biology of size and gravity]

Gravity is a force that acts on mass. Biological effects of gravity and their magnitude depend on scale of mass and difference in density. One significant contribution of space biology is confirmation of direct action of gravity even at the cellular level. Since cell is the elementary unit of life, existence of primary effects of gravity on cells leads to establish the firm basis of gravitational biology. However, gravity is not limited to produce its biological effects on molecules and their reaction networks that compose living cells. Biological system has hierarchical structure with layers of organism, group, and ecological system, which emerge from the system one layer down. Influence of gravity is higher at larger mass. In addition to this, actions of gravity in each layer are caused by process and mechanism that is subjected and different in each layer of the hierarchy. Because of this feature, summing up gravitational action on cells does not explain gravity for biological system at upper layers. Gravity at ecological system or organismal level can not reduced to cellular mechanism. Size of cells and organisms is one of fundamental characters of them and a determinant in their design of form and function. Size closely relates to other physical quantities, such as mass, volume, and surface area. Gravity produces weight of mass. Organisms are required to equip components to support weight and to resist against force that arise at movement of body or a part of it. Volume and surface area associate with mass and heat transport process at body. Gravity dominates those processes by inducing natural convection around organisms. This review covers various elements and process, with which gravity make influence on living systems, chosen on the basis of biology of size. Cells and biochemical networks are under the control of organism to integrate a consolidated form. How cells adjust metabolic rate to meet to the size of the composed organism, whether is gravity responsible for this feature, are subject we discuss in this article. Three major topics in gravitational and space biology are; how living systems have been adapted to terrestrial gravity and evolved, how living systems respond to exotic gravitational environment, and whether living systems could respond and adapt to microgravity. Biology of size can contribute to find a way to answer these question, and answer why gravity is important in biology, at explaining why gravity has been a dominant factor through the evolutional history on the earth.     

Effects of microgravity and clinostating on plants

Abstract

Results of many space flight and clinostate experiments performed with growing and developing lower and higher plants, tissue and protoplast cultures are presented. Biological effects of gravity changes on organism, cellular, subcellular and membrane levels are described. Regularities of rearrangements of organelle structural-functional organizations and cell metabolism as well as possible cell mechanisms of the adaptation to microgravity are discussed.     

Gravitation biology using fish as model systems for understanding motion sickness susceptibility

During the entire evolution of life on Earth, the development of all organisms took place under constant gravity conditions, against which they achieved specific countermeasures for compensation and adaptation. On this background, it is still an open question to which extent altered gravity such as hyper- or microgravity (centrifuge/spaceflight) affects the normal individual development, either on the systemic level of the whole organism or on the level of individual organs or even single cells. The present short review provides information on this topic, focusing on the effects of altered gravity on developing fish as model systems even for higher vertebrates including humans, with special emphasis on the effect of altered gravity on behaviour and particularly on the developing brain and vestibular system.     

Manifestations of ageing at the cytogenetic level

The effects of ageing in humans appear to be a combination of influence of genetically programmed phenomena and exogenous environmental factors, and take place at the cellular level (senescence), rather than at the level of the organism. There are many processes, which occur in somatic cells as a consequence of DNA replication (accumulation of DNA errors or mutations that outstrip repair processes, telomere shortening, deregulation of apoptosis, etc.) and which drive replicative senescence in human cells. DNA errors are considered to be critical primary lesions in the formation of chromosomal aberrations. It can be concluded that the chromosome aberrations are biomarkers of ageing in human cells. Studies of human metaphases, interphase nuclei and micronuclei showed the increase in loss of chromosomes and the increase in frequency of stable chromosome aberrations as a function of age.     

Evaluating spread of invaders from gravity scores - A way of using gravity models in ecology

This study is a theoretical excursion into gravity models and their usability in evaluating importance of spatial structure and population development for the spread of colonizing organisms. A so called “gravity score” for sites is deduced, and such a score could be used for predicting risk of colonization once one site in an area has been subject to introduction of a new species. The analysis further suggests that factors deciding spread between sites differs from those that govern expected population sizes. Gravity models of the kind presented here includes both population dynamics and spatial structure and could be a complement to other models describing organism spread.     

Molecular aspects of stress-gene regulation during spaceflight

Spaceflight-associated stress has been the topic of investigation since the first terrestrial organisms were exposed to this unique environment. Organisms that evolved under the selection pressures of earth-normal environments can perceive spaceflight as a stress, either directly because gravity influences an intrinsic biological process, or indirectly because of secondary effects imparted by spaceflight upon environmental conditions. Different organisms and even different organs within an organism adapt to a spaceflight environment with a diversity of tactics. Plants are keenly sensitive to gravity for directed development, and are also sensitive to other stresses associated with closed-system spaceflight environments. Within the past decade, the tools of molecular biology have begun to provide a sophisticated evaluation of spaceflight-associated stress and the genetic responses that accompany metabolic adaptation to spaceflight.     

Endocrine responses to space flights

Simultaneously with human space flights several series of observations were performed by using experimental animals--mainly rats--exposed to space flights on board of special satellites BION-COSMOS or in Shuttle Transportation Systems (STS). The aims of these experiments were to study in more details: the mechanisms of the changes in bones and skeletal muscle, the alterations of the function of immune system, the radiation effects on organism, the mechanism of the changes of endocrine functions, the evaluation of the role of hormones in alteration of metabolic processes in organism. The advantages of these animal experiments were the possibilities to analyze not only the plasma samples, but it was possible to obtain samples of organs or tissues: for morphological and biochemical analysis for studies of the changes in enzyme activities and in gene expressions, for measurement of metabolic processes and for investigation of the hormone production in endocrine glands and estimation of the response of tissues to hormones. It was also possible to compare the endocrine response to spaceflight and to other stress stimuli. These animal studies are interesting for verification of some hypothesis in the mechanism of adaptation of human organism to the changes of gravity. The disadvantage was, however, that the animals in almost all experiments could be examined only after space flight. The actual inflight changes were investigated only in two SLS flights. In this short review it is not possible to evaluate all hormonal data available on the response of endocrine system to the conditions of space flights. Therefore we will concentrate on the response of pituitary adrenocortical system, pituitary thyroid and pituitary gonadal functions.     

Signal transduction in cells of the immune system in microgravity

Life on Earth developed in the presence and under the constant influence of gravity. Gravity has been present during the entire evolution, from the first organic molecule to mammals and humans. Modern research revealed clearly that gravity is important, probably indispensable for the function of living systems, from unicellular organisms to men. Thus, gravity research is no more or less a fundamental question about the conditions of life on Earth. Since the first space missions and supported thereafter by a multitude of space and ground-based experiments, it is well known that immune cell function is severely suppressed in microgravity, which renders the cells of the immune system an ideal model organism to investigate the influence of gravity on the cellular and molecular level. Here we review the current knowledge about the question, if and how cellular signal transduction depends on the existence of gravity, with special focus on cells of the immune system. Since immune cell function is fundamental to keep the organism under imnological surveillance during the defence against pathogens, to investigate the effects and possible molecular mechanisms of altered gravity is indispensable for long-term space flights to Earth Moon or Mars. Thus, understanding the impact of gravity on cellular functions on Earth will provide not only important informations about the development of life on Earth, but also for therapeutic and preventive strategies to cope successfully with medical problems during space exploration.     

Root movements: Towards an understanding through attempts to model the processes involved

Roots have the ability to change the direction of their forward growth. Sometimes these directional changes are rapid, as in mutations, or they are slower, as in tropisms. The gravitational force is always present and roots have an efficient graviperception mechanism which enables them to initiate gravitropic movements. In trying to model and simulate the course of gravitropic root movements with a view to analyse the component processes, the following aspects of the plant's interaction with gravity have been considered: (1) The level of organization (organism, organ, cell) at which the movement process is expressed; (2) whether the gravity stimulation event is dynamic or static (i.e. whether or not physiologically significant displacements take place with respect to the gravity vector); (3) the sub-systems involved in movement and the processes which they regulate; (4) the mathematical characterization of the relevant sub-systems. A further allied topic is the nature of nutational movements and whether they are linked with gravitropic movements in some way. In considering how they can best be modelled, two types of nutational movements are proponed: stochastic nutation and circumnutation. Most, if not all, natural movements developed in response to static gravistimulation can be viewed as gravimorphisms. This applies at the levels of cell, organ and organism. However, when a system at any one of these levels experiences dynamic gravistimulation, because of its inherent homeostatic properties, it is induced to regenerate a state similar to that previously held. Thus, gravitropism is a regenerative gravimorphic process at the level of the organ.     

Induction of PXR-mediated metabolism by beta-carotene

beta-carotene is the major carotenoid occurring in the human diet and in the human organism. Besides its function as pro-vitamin A, beta-carotene has been shown to be an activator of the human pregnan X receptor (PXR). PXR is mainly expressed in the liver/intestine and an inducer of enzymes involved in phase I, II and III metabolism. This review is focused on the evaluation of physiological and nutritional relevance of beta-carotene as an inducer of phase I enzymes in the human organism via PXR-mediated mechanisms. Beneficial and detrimental effects of beta-carotene on xenobiotica metabolism and metabolism of various other derivatives will be discussed.     

The effects of gravity on the circadian timing system

The physiological system responsible for the temporal coordination of an organism is the circadian timing system (CTS). This system provides two forms of temporal coordination. First, the CTS provides for synchronization of the organism with the 24 hour period of the external environment. This synchronization of the organism with the environment is termed entrainment. Second, this system also provides for internal coordination of the various physiological, behavioral, and biochemical events within the organism. When either of these two temporal relationships are disturbed, various dysfunctions can be manifest within the organism. Homeostatic capacity of other physiological systems may be reduced. Performance is decreased and sleep disorders, mental health impairment (e.g., depression), jet lag syndrome, and shift work maladaptation frequently occur. Over the last several years, several studies have evaluated the potential influence of gravity on this physiological control system by examining changes in rhythmic characteristics of organisms exposed to altered gravitational environments. The altered gravitational environments have included the microgravity of spaceflight as well as hyperdynamic fields produced via centrifugation.     

Suspension cultures of human malignant lymphoma in the leukocyte migration test

The effects of supernatants of primary and secondary malignant human lymphoma cell cultures were analyzed as parameters of spontaneous secretion of factors by these cells using the leukocyte migration test (LMT). Spontaneous cultivation for up to five weeks was successful in four cases. The postulated production of mediators, i.e. the inhibitory and stimulating effects on leukocyte migration were characterized by testing the influence of (a) concentration, (b) temperature and (c) absorption with normal blood leukocytes on the effect. Reproducible stimulatory and inhibitory effects on the migration of normal leukocytes were dependent on concentration and temperature and were apparently mediated by one or more factors. The supernatants of a lymphoblastic lymphosarcoma of the T-cell type and of a lymphoblastic lymphosarcoma clearly revealed congruous and reproducible inhibitory effects. A further case of lymphoblastic lymphosarcoma that could not exactly be defined with immunological methods either and a case of centroblastic/centrocytic lymphosarcoma exhibited stimulating effects which could be reduced in a time-dependent manner through preincubation with blood leukocytes. The results of these studies support the assumption that malignant lymphoma cells are capable not only of secreting immunoglobulin, but also of other biologically effective secretion. The effects of such secretion are differentiated into stimulating and inhibitory ones. They might be important for the spreading of a tumor or for resistance of the organism to the disease.     

A mechanism conjugating cellular and individual adaptations could be produced from space biology]

To know a basic mechanism of biological organism on the earth, we can have a standard point to space. An example is hindlimb suspension model that could induce muscle atrophy. This model mimics adaptational changes under zero gravity; in turn the effect of gravity on the biological system developing on the earth. We can understand gravity is a stress from the specific changes of stress protein induced by mechanical stimuli depending on gravity. Recent development of fluorescent microscopy and time-lapse visual system brought us a possibility of analysis to see visualization of dynamic properties of molecular and cellular events in living cells. Especially dynamic fluctuation of cytoskeleton may include new ideas of biological strategy of living organism on the earth and possibly may suggest subtle changes in space.     

Artificial gravity in space and in medical research

The history of manned space flight has repeatedly documented the fact that prolonged sojourn in space causes physiological deconditioning. Physiological deterioration has raised a legitimate concern about man's ability to adequately perform in the course of long missions and even the possibility of leading to circumstances threatening survival. One of the possible countermeasures of physiological deconditioning, theoretically more complete than others presently used since it affects all bodily systems, is artificial gravity. Space stations and spacecrafts can be equipped with artificial gravity, but is artificial gravity necessary? The term "necessary" must be qualified because a meaningful answer to the question depends entirely on further defining the purpose of space travel. If man intends to stay only temporarily in space, then he must keep himself in good physical condition so as to be able to return to earth or to land on any other planetary surface without undue exposure to major physiological problems resulting from transition through variable gravitational fields. Such a situation makes artificial gravity highly desirable, although perhaps not absolutely necessary in the case of relative short exposure to microgravity, but certainly necessary in interplanetary flight and planetary landings. If the intent is to remain indefinitely in space, to colonize space, then artificial gravity may not be necessary, but in this case the consequences of long term effects of adaptation to weightlessness will have to be weighed against the biological evolutionary outcomes that are to be expected. At the moment, plans for establishing permanent colonies in space seem still remote. More likely, the initial phase of exploration of the uncharted solar system will take place through successive, scope limited, research ventures ending with return to earth. This will require man to be ready to operate in gravitational fields of variable intensity. Equipping spacecrafts or space stations with some means of artificial gravity in this initial phase is, therefore, necessary without question. In a strict sense artificial gravity is conceived as a means of replacing natural gravity in space by the centripetal acceleration generated by some sort of rotating device. Rotating devices create an inertial force which has effects on bodies similar to those caused by terrestrial gravity, but artificial gravity by a rotation device is not the same as terrestrial gravity, as we shall see. Present research in artificial gravity for space exploration is projected in two main directions: artificial gravity for whole space stations and artificial gravity produced by short arm centrifuges designed for human use in space.     

Defining life from death: Problems with the somatic integration definition of life

To determine when the life of a human organism begins, Mark T. Brown has developed the somatic integration definition of life. Derived from diagnostic criteria for human death, Brown’s account requires the presence of a life-regulation internal control system for an entity to be considered a living organism. According to Brown, the earliest point at which a developing human could satisfy this requirement is at the beginning of the fetal stage, and so the embryo is not regarded as a living human organism. This, Brown claims, has significant bioethical implications for both abortion and embryo experimentation. Here, we dispute the cogency of Brown’s derivation. Diagnostic criteria for death are used to determine when an organism irreversibly ceases functioning as an integrated whole, and may vary significantly depending on how developed the organism is. Brown’s definition is derived from a specific definition of death applicable to postnatal human beings, which is insufficient for generating a general definition for human organismal life. We have also examined the bioethical implications of Brown’s view, and have concluded that they are not as significant as he believes. Whether the embryo is classified as a human organism is of peripheral interest—a far more morally relevant question is whether the embryo is a biological individual with an identity that is capable of persisting during development.     

Gravity: It's the law

Based on experience in microgravity and on centrifuge induced hypergravity, exposure to either altered force field causes marked effects in animals and humans. It would seem logical that changes from unit gravity would have different effects depending on whether gravity is increased or decreased. Examples will be presented of responses to altered gravitational fields and changes in human and animal musculoskeletal, cardiopulmonary neurovestibular and metabolic responses.     

Effect of inorganic fluoride on living organisms of different phylogenetic level

This review summarizes literature data on pathways of inorganic fluoride intake to the plant, animal and human organisms, its metabolism, distribution and accumulation in the organism, the fluoride forms in biological tissues, toxic effects of fluoride on physiological and reproductive functions of living organisms of different phylogenetic groups, as well as clinical symptoms of insufficient and excessive intake of fluoride in human organism.     

Molecular and cellular interactions between mother and fetus. Pregnancy as a rejuvenating factor

Aging is associated with a decline of various body functions, including ability to regenerate. Over recent decades, it has been demonstrated that some of these changes could be reversed in response to factors originating from a young organism, for example, fetal stem cells or “young blood” in models of heterochronic parabiosis. Pregnancy might be considered as parabiotic model of the interaction between two organisms of different age. In this work, we analyzed and summarized data on the effects of pregnancy on the maternal organism that confirm the hypothesis that pregnancy rejuvenates the mother’s organism or slows its aging.     

Development of real-time PCR assays for rapid detection of Pfiesteria piscicida and related dinoflagellates

Pfiesteria complex species are heterotrophic and mixotrophic dinoflagellates that have been recognized as harmful algal bloom species associated with adverse fish and human health effects along the East Coast of North America, particularly in its largest (Chesapeake Bay in Maryland) and second largest (Albermarle-Pamlico Sound in North Carolina) estuaries. In response to impacts on human health and the economy, monitoring programs to detect the organism have been implemented in affected areas. However, until recently, specific identification of the two toxic species known thus far, Pfiesteria piscicida and P. shumwayae (sp. nov.), required scanning electron microscopy (SEM). SEM is a labor-intensive process in which a small number of cells can be analyzed, posing limitations when the method is applied to environmental estuarine water samples. To overcome these problems, we developed a real-time PCR-based assay that permits rapid and specific identification of these organisms in culture and heterogeneous environmental water samples. Various factors likely to be encountered when assessing environmental samples were addressed, and assay specificity was validated through screening of a comprehensive panel of cultures, including the two recognized Pfiesteria species, morphologically similar species, and a wide range of other estuarine dinoflagellates. Assay sensitivity and sample stability were established for both unpreserved and fixative (acidic Lugol's solution)-preserved samples. The effects of background DNA on organism detection and enumeration were also explored, and based on these results, we conclude that the assay may be utilized to derive quantitative data. This real-time PCR-based method will be useful for many other applications, including adaptation for field-based technology.     

Membrane-associated hemolysin activities in mycoplasmas

Abstract Mycoplasmas are cell wall-less organisms that require membrane precursors for growth. Activities involved in the acquisition of these materials have been hypothesized as mycoplasmal virulence factors because of the effects these activities might have on host cells. Twenty-nine species or strains of mycoplasmas were examined for membrane-associated hemolysis activity similar to that previously identified in Mycoplasma pulmonis . Membrane-associated hemolytic activity was found in most mycoplasma species, but the amount of activity varied between and within the species. All of the arginine-utilizing mycoplasmal species, one M. pulmonis strain, one Acholeplasma species, and the intracellular human pathogens M. penetrans and M. fermentans ssp. incognitus were devoid of activity. The wide distribution of the membrane-associated hemolysis activity suggests that it may be important to the survival of the organism.