Space Microgravity Research Articles

Microgravity-induced stress mechanisms in human stem cell-derived cardiomyocytes

SummaryExposure to outer space microgravity poses a risk for the development of various pathologies including cardiovascular disease. To study this, we derived cardiomyocytes (CMs) from human-induced pluripotent stem cells and exposed them to simulated microgravity (SMG). We combined different “omics” and chromosome conformation capture technologies with live-cell imaging of various transgenic lines to discover that SMG impacts on the contractile velocity and function of CMs via the induction of senescence processes. This is linked to SMG-induced changes of reactive oxygen species (ROS) generation and energy metabolism by mitochondria. Taken together, we uncover a microgravity-controlled axis causing contractile dysfunctions to CMs. Our findings can contribute to the design of preventive and therapeutic strategies against senescence-associated disease.

Delayed Maturation of Oligodendrocyte Progenitors by Microgravity: Implications for Multiple Sclerosis and Space Flight.

In previous studies, we examined the effects of space microgravity on human neural stem cells. To date, there are no studies on a different type of cell that is critical for myelination and electrical signals transmission, oligodendrocyte progenitors (OLPs). The purpose of the present study was to examine the behavior of space-flown OLPs (SPC-OLPs) as they were adapting to Earth’s gravity. We found that SPC-OLPs survived, and most of them proliferated normally. Nonetheless, some of them displayed incomplete cytokinesis. Both morphological and ontogenetic analyses showed that they remained healthy and expressed the immature OLP markers Sox2, PDGFR-α, and transferrin (Tf) after space flight, which confirmed that SPC-OLPs displayed a more immature phenotype than their ground control (GC) counterparts. In contrast, GC OLPs expressed markers that usually appear later (GPDH, O4, and ferritin), indicating a delay in SPC-OLPs’ development. These cells remained immature even after treatment with culture media designed to support oligodendrocyte (OL) maturation. The most remarkable and surprising finding was that the iron carrier glycoprotein Tf, previously described as an early marker for OLPs, was expressed ectopically in the nucleus of all SPC-OLPs. In contrast, their GC counterparts expressed it exclusively in the cytoplasm, as previously described. In addition, analysis of the secretome demonstrated that SPC-OLPs contained 3.5 times more Tf than that of GC cells, indicating that Tf is gravitationally regulated, opening two main fields of study to understand the upregulation of the Tf gene and secretion of the protein that keep OLPs at a progenitor stage rather than moving forward to more mature phenotypes. Alternatively, because Tf is an autocrine and paracrine factor in the central nervous system (CNS), in the absence of neurons, it accumulated in the secretome collected after space flight. We conclude that microgravity is becoming a novel platform to study why in some myelin disorders OLPs are present but do not mature.

Aerospace Technology Improves Fermentation Potential of Microorganisms.

It is highly possible to obtain high-quality microbial products in appreciable amounts, as aerospace technology is advancing continuously. Genome-wide genetic variations in microorganisms can be triggered by space microgravity and radiation. Mutation rate is high, mutant range is wide, and final mutant character is stable. Therefore, space microorganism breeding is growing to be a new and promising area in microbial science and has greatly propelled the development of fermentation technology. Numerous studies have discovered the following improvements of fermentation potential in microorganisms after exposure to space: (1) reduction in fermentation cycle and increase in growth rate; (2) improvement of mixed fermentation species; (3) increase in bacterial conjugation efficiency and motility; (4) improvement of the bioactivity of various key enzymes and product quality; (5) enhancement of multiple adverse stress resistance; (6) improvement of fermentation metabolites, flavor, appearance, and stability. Aerospace fermentation technology predominantly contributes to bioprocessing in a microgravity environment. Unlike terrestrial fermentation, aerospace fermentation keeps cells suspended in the fluid medium without significant shear forces. Space radiation and microgravity have physical, chemical, and biological effects on mutant microorganisms by causing alternation in fluid dynamics and genome, transcriptome, proteome, and metabolome levels.

Cryogenic spray quenching of simulated propellant tank wall using coating and flow pulsing in microgravity

In-space cryogenic propulsion will play a vital role in NASA’s return to the Moon mission and future mission to Mars. The enabling of in-space cryogenic engines and cryogenic fuel depots for these future manned and robotic space exploration missions begins with the technology development of advanced cryogenic thermal-fluid management systems for the propellant transfer lines and storage system. Before single-phase liquid can flow to the engine or spacecraft receiver tank, the connecting transfer line and storage tank must first be chilled down to cryogenic temperatures. The most direct and simplest method to quench the line and the tank is to use the cold propellant itself that results in the requirement of minimizing propellant consumption during chilldown. In view of the needs stated above, a highly efficient thermal-fluid management technology must be developed to consume the minimum amount of cryogen during chilldown of a transfer line and a storage tank. In this paper, we suggest the use of the cryogenic spray for storage tank chilldown. We have successfully demonstrated its feasibility and high efficiency in a simulated space microgravity condition. In order to maximize the storage tank chilldown efficiency for the least amount of cryogen consumption, the technology adopted included cryogenic spray cooling, Teflon thin-film coating of the simulated tank surface, and spray flow pulsing. The completed flight experiments successfully demonstrated that spray cooling is the most efficient cooling method for the tank chilldown in microgravity. In microgravity, Teflon coating alone can improve the efficiency up to 72% and the efficiency can be improved up to 59% by flow pulsing alone. However, Teflon coating together with flow pulsing was found to substantially enhance the chilldown efficiency in microgravity for up to 113%.

Muscle synergies of multidirectional postural control in astronauts on Earth after a long-term stay in space.

Movements of the human biological system have adapted to the physical environment under the 1-g gravitational force on Earth. However, the effects of microgravity in space on the underlying functional neuromuscular control behaviors remain poorly understood. Here, we aimed to elucidate the effects of prolonged exposure to a microgravity environment on the functional coordination of multiple muscle activities. The activities of 16 lower limb muscles of 5 astronauts who stayed in space for at least 3 mo were recorded while they maintained multidirectional postural control during bipedal standing. The coordinated activation patterns of groups of muscles, i.e., muscle synergies, were estimated from the muscle activation datasets using a factorization algorithm. The experiments were repeated a total of five times for each astronaut, once before and four times after spaceflight. The compositions of muscle synergies were altered, with a constant number of synergies, after long-term exposure to microgravity, and the extent of the changes was correlated with the increased velocity of postural sway. Furthermore, the muscle synergies extracted 3 mo after the return were similar in their activation profile but not in their muscle composition compared with those extracted in the preflight condition. These results suggest that the modularity in the neuromuscular system became reorganized to adapt to the microgravity environment and then possibly reoptimized to the new sensorimotor environment after the astronauts were reexposed to a gravitational force. It is expected that muscle synergies can be used as physiological markers of the status of astronauts with gravity-dependent change.NEW & NOTEWORTHY The human neuromuscular system has adapted to the gravitational environment on Earth. Here, we demonstrated that prolonged exposure to a microgravity environment in space changes the functional coordination of multiple muscle activities regarding multidirectional standing postural control. Furthermore, the amount of change led to a greater regulatory balancing activity needed for postural control immediately after returning to Earth and differences in muscular coordination before space flight and 3 mo after the return to Earth.

Suppression of Cortical Microtubule Reorientation and Stimulation of Cell Elongation in Arabidopsis Hypocotyls under Microgravity Conditions in Space.

How microgravity in space influences plant cell growth is an important issue for plant cell biology as well as space biology. We investigated the role of cortical microtubules in the stimulation of elongation growth in Arabidopsis (Arabidopsis thaliana) hypocotyls under microgravity conditions with the Resist Tubule space experiment. The epidermal cells in the lower half of the hypocotyls of wild-type Columbia were longer in microgravity than at on-orbit 1 g, which precipitated an increase in the entire hypocotyl length. In the apical region, cortical microtubules adjacent to the outer tangential wall were predominantly transverse to the long axis of the cell, whereas longitudinal microtubules were predominant in the basal region. In the 9th to 12th epidermal cells (1 to 3 mm) from the tip, where the modification of microtubule orientation from transverse to longitudinal directions (reorientation) occurred, cells with transverse microtubules increased, whereas those with longitudinal microtubules decreased in microgravity, and the average angle with respect to the transverse cell axis decreased, indicating that the reorientation was suppressed in microgravity. The expression of tubulin genes was suppressed in microgravity. These results suggest that under microgravity conditions, the expression of genes related to microtubule formation was downregulated, which may cause the suppression of microtubule reorientation from transverse to longitudinal directions, thereby stimulating cell elongation in Arabidopsis hypocotyls.

Cells respond to space microgravity through cytoskeleton reorganization.

Decades of spaceflight studies have provided abundant evidence that individual cells in vitro are capable of sensing space microgravity and responding with cellular changes both structurally and functionally. However, how microgravity is perceived, transmitted, and converted to biochemical signals by single cells remains unrevealed. Here in this review, over 40 cellular biology studies of real space fights were summarized. Studies on cells of the musculoskeletal system, cardiovascular system, and immune system were covered. Among all the reported cellular changes in response to space microgravity, cytoskeleton (CSK) reorganization emerges as a key indicator. Based on the evidence of CSK reorganization from space flight research, a possible mechanism from the standpoint of "cellular mechanical equilibrium" is proposed for the explanation of cellular response to space microgravity. Cytoskeletal equilibrium is broken by the gravitational change from ground to space and is followed by cellular morphological changes, cell mechanical properties changes, extracellular matrix reorganization, as well as signaling pathway activation/inactivation, all of which ultimately lead to the cell functional changes in space microgravity.

NOVEL APPROACH FOR FRACTAL NONLINEAR OSCILLATORS WITH DISCONTINUITIES BY FOURIER SERIES

This paper argues that in the microgravity space, the fractal nonlinear oscillators’ models with discontinuities are established by the fractal calculus, and their fractal variational principles are obtained via using the fractal semi-inverse method. Finally, a novel technology is proposed to find the frequency of the fractal nonlinear oscillators’ model by using the Fourier series. The results illustrate that the proposed method is efficient and accurate.

Characteristics of blood plasma proteome changes associated with the hemorrhagic purpura of cosmonauts on the first day after long-term space missions

The interest in the role of the gravitational factor during landing after long-term space flights (SF) leads to the search for various innovative approaches to assessing the compliance of external changes observed by clinicians. The results of special research methods such as Omics technologies that may reflect physiological responses to the conditions created during landing are of great interest. Our purpose is to compare the blood plasma proteome changes associated with the trauma and endothelial dysfunction processes prior to launch and on the day of landing, as well as the groups of cosmonauts with and without the secondary hemorrhagic purpura. In our study, the concentrations of 125 plasma proteins in 18 Russian cosmonauts, measured using targeted proteomic analysis based on liquid chromatography and tandem mass spectrometry were analyzed. The results reveal the trends of 12 proteins participating in the processes that trigger hemorrhagic purpura under the effect of re-entry g-forces. Exposure to intense g-forces and return to the gravity are the key factors for external manifestations of changes in the body systems induced by a long-term stay in space microgravity. Our results may be useful for further research to experts in gravitational physiology, aviation and space medicine.

Simulated Microgravity Increases the Permeability of HUVEC Monolayer through Up-Regulation of Rap1GAP and Decreased Rap2 Activation.

Space microgravity condition has great physiological influence on astronauts’ health. The interaction of endothelial cells, which control vascular permeability and immune responses, is sensitive to mechanical stress. However, whether microgravity has significant effects on the physiological function of the endothelium has not been investigated. In order to address such a question, a clinostat-based culture model with a HUVEC monolayer being inside the culture vessel under the simulated microgravity (SMG) was established. The transmittance of FITC-tagged dextran was used to estimate the change of integrity of the adherens junction of the HUVEC monolayer. Firstly, we found that the permeability of the HUVEC monolayer was largely increased after SMG treatment. To elucidate the mechanism of the increased permeability of the HUVEC monolayer under SMG, the levels of total expression and activated protein levels of Rap1 and Rap2 in HUVEC cells, which regulate the adherens junction of endothelial cells, were detected by WB and GST pull-down after SMG. As the activation of both Rap1 and Rap2 was significantly decreased under SMG, the expression of Rap1GEF1 (C3G) and Rap1GAP in HUVECs, which regulate the activation of them, was further determined. The results indicate that both C3G and Rap1GAP showed a time-dependent increase with the expression of Rap1GAP being dominant at 48 h after SMG. The down-regulation of the expression of junctional proteins, VE-cadherin and β-catenin, in HUVEC cells was also confirmed by WB and immunofluorescence after SMG. To clarify whether up-regulation of Rap1GAP is necessary for the increased permeability of the HUVEC monolayer after SMG, the expression of Rap1GAP was knocked down by Rap1GAP-shRNA, and the change of permeability of the HUVEC monolayer was detected. The results indicate that knock-down of Rap1GAP reduced SMG-induced leaking of the HUVEC monolayer in a time-dependent manner. In total, our results indicate that the Rap1GAP-Rap signal axis was necessary for the increased permeability of the HUVEC monolayer along with the down-regulation of junctional molecules including VE-cadherin and β-catenin.

ГЛАДКАЯ МЫШЕЧНАЯ ТКАНЬ – ПЕРСПЕКТИВНАЯ МИШЕНЬ ТРАНСЛЯЦИОННЫХ ИССЛЕДОВАНИЙ В КОСМИЧЕСКОЙ БИОМЕДИЦИНЕ

This is an overview of the current knowledge of the structural and functional organization of the smooth muscle tissue (SMT) presenting equally fundamental and applied interest for space biomedicine. SMT is a structural component of the visceral organs involved in adaptive reactions or pathological developments. According to the evidence, cell populations of visceral SMT contain smooth myocites differing in histophysiological properties. Many investigators reason that the SMT morphological and embriological origin is organ-specific and can be an area of translational researches, including space biomedicine. In spite of the multisided analysis of animal and humans tissues exposed to the spaceflight factors, no effort has been made to study SMT in space microgravity or ground-based modeling experiments. However, space gastroenterology knows facts about morphological transformations in the digestive organs in the spaceflight environment. Clearly, SMT as a structural component of the gastrointestinal tract may contribute directly in a number of organ-specific changes during orbital missions. SMT studies will unveil mechanisms of adaptive cell, and molecular changes with stromal mediation due to microgravity, and reveal targets for enhancing health control in space missions.

ИЗУЧЕНИЕ АКТИВНОСТИ ЦЕНТРАЛЬНОГО ДЫХАТЕЛЬНОГО МЕХАНИЗМА В УСЛОВИЯХ ДЛИТЕЛЬНОГО КОСМИЧЕСКОГО ПОЛЕТА

Interrelation between blood redistribution toward the upper part of the body in microgravity and changes in sensitivity of the central respiratory mechanism was studied with participation of 16 Russian members of the International space station crews (40-57 year-old males). Time of maximal voluntary breath-holding during inspiration (MVHins) and expiration (MVHexp) was measured prior to and following the 15-min low-body negative pressure test (LBNP, -25 mm Hg). Before launch, the baseline MVHins and MVHexp durations in the vertical position made up 61.9 ± 3.9 s and 24.5 ± 1.5 s, respectively. In the supine position, the parameters increased to 81.1 ± 5.6 s and 31.2 ± 1.9 s (p < 0.01), respectively. More significant increases of breath-holding were observed in space microgravity. On flight months 1-5, MVHins and MVHexp rose by 25–45.5 % and by 17.5–54.2 %, respectively. After return from space the initial values of the parameters were recovered. Comparison of the measurements made prior to and within 5-10 minutes after LBNP revealed a further gain in both MVHins and MVHexp. Breath-holding extension in the supine position (at 1 G) and in microgravity suggests attenuation of the respiratory center sensitivity to the physiological chemoreceptor stimuli, namely, increased РаСО2 and lowered РаО2. This attenuation is driven by the blood shift toward the upper part of the body that causes increase of the vascular pressure in the sinus carotid region and activation of baroreceptors. The conclusion results from the significantly greater time of breath-holding during LBNP in microgravity and supine position, as well as time reduction to the initial values on return from space mission.

Electromagnetic field induced alterations in fluid flow through lacuno-canalicular system of bone

Osteoporosis, bone-muscle disuse, and long-term exposure to space microgravity cause bone loss and promote bone fractures. Therapeutic devices and interventions for the prevention of bone loss and regulation of fracture healing are serious challenges for orthopaedic clinicians and researchers. Electromagnetic field exposure in combination with mechanical loading has the potential to prevent disuse bone loss as it promotes osteogenesis i.e., new bone formation. Loading-induced fluid motion in lacunar space acts as a stimulus for osteo-activities. Nevertheless, how the electromagnetic field regulates biomechanical stimulus such as fluid motion required for osteogenesis within bone tissue is not well understood. Accordingly, this paper attempts to establish a mathematical model to investigate the role of electromagnetic fields to alter the cantilever bending-induced lacunar fluid flow behaviour. A more realistic curvy canalicular channel subjected to electrohydrodynamics (EHD) mechanism is modelled to study poromechanical and canalicular fluid flow parameters such as pore-pressure gradient, fluid velocity, wall shear, and streamline patterns. Computational results indicate that electromagnetic fields modulate the fluid motion required for osteogenic activities even in bone tissues with higher porosity and permeability. The present study explains how electromagnetic fields possibly modulate mechanobiological stimulus in bone tissue. Based on the outcomes, an optimal loading regimen along with the electromagnetic field can be selected to enhance osteogenic response to prevent and mitigate irreversible bone loss that occurred due to microgravity and disuse.

Mimic microgravity effect on muscle transcriptome under ionizing radiation

Spaceflight imposes the risk of skeletal muscle atrophy for astronauts. Two main factors of a spaceflight that results in deleterious effects are microgravity and cosmic rays in outer space. To study spaceflight-induced muscle atrophy with ground-based models, we performed two models of microgravity, tail suspension and denervation, in a low dose radiation environment and studied transcriptional changes in rat soleus muscle using microarrays. Soleus muscle from rats in the denervation group had greater expression changes compared to that found in rats from the tail suspension group. However, there was a very similar pattern of expression of differentially expressed genes (DEGs) in both models. In total, we identified 144 differentially expressed genes common in both models. Our study yielded two main findings. First, a large number of genes involved in energy metabolism were transcriptionally suppressed including those involved in fatty acid transport and beta-oxidation, and oxidative phosphorylation. Second, slow-twitch contractile protein encoding genes were down-regulated while there was an up-regulation in the fast-twitch type transcription. These results were consistent with other spaceflight studies on the effects on muscle cells, hence showed the potential of our ground-based models in studying spaceflight effects. The genes that might be involved in spaceflight effects will serve as candidate genes for future studies in understanding the mechanism of spaceflight-induced muscle atrophy and result in the development of effective countermeasures.

Changes in Exosomal miRNA Composition in Thyroid Cancer Cells after Prolonged Exposure to Real Microgravity in Space.

As much as space travel and exploration have been a goal since humankind looked up to the stars, the challenges coming with it are manifold and difficult to overcome. Therefore, researching the changes the human organism undergoes following exposure to weightlessness, on a cellular or a physiological level, is imperative to reach the goal of exploring space and new planets. Building on the results of our CellBox-1 experiment, where thyroid cancer cells were flown to the International Space Station, we are now taking advantage of the newest technological opportunities to gain more insight into the changes in cell–cell communication of these cells. Analyzing the exosomal microRNA composition after several days of microgravity might elucidate some of the proteomic changes we have reported earlier. An array scan of a total of 754 miRNA targets revealed more than 100 differentially expressed miRNAs in our samples, many of which have been implicated in thyroid disease in other studies.

Understanding the Mechanisms of Gravity Resistance in Plants.

To understand gravity resistance in plants, it is necessary to analyze the changes induced when the magnitude of gravity in a growth environment is modified. Microgravity in space provides appropriate conditions for analyzing gravity resistance mechanisms. Experiments carried out in space involve a large number of constraints and are quite different from ground-based experiments. Here, we describe basic procedures for space-based experiments to study gravity resistance in plants. An appropriate cultivation chamber must be selected according to the growing period of the plants and the purpose of the experiment. After cultivation, the plant material is fixed with suitable fixatives in appropriate sample storage containers such as the Chemical Fixation Bag. The material is then analyzed with a variety of methods, depending on the purpose of the experiment. Plant material fixed with the RNAlater® solution can be used sequentially to determine the mechanical properties of the cell wall, RNA extraction (which is necessary for gene-expression analysis), estimate the enzyme activity of cell wall proteins, and measure the levels and compositions of cell wall polysaccharides. The plant material can also be used directly for microscopic observation of cellular components such as cortical microtubules.

Nanoscale Reciprocating Sliding Contact Behaviors of an Isosceles Trapezoid Textured Surface in Space Environment

Background: In the space environment, microgravity and vacuum influence the mechanical behaviors of the devices. In the microgravity environment, the mechanical components vibrate with a small amplitude once there is a disturbance. The vibration can be seen as a reciprocating sliding contact with a small amplitude. In addition to the vibration, adhesion effects are predominant in a vacuum, which will induce a high friction force. Objective: To reduce the friction force, textured surfaces are widely used in mechanical engineering on the earth, and nanoscale textures are also verified to be used to improve the frictional behaviors of components in the size of nanometers. Methods: In this paper, the adhesion effects are considered by using molecular dynamics (MD) simulation, and the microgravity induced vibration is simplified as a reciprocating sliding contact. Coupling MD simulation and the finite element method which is a multiscale method are used to investigate the frictional properties of nanoscale reciprocating sliding contact between rigid multiasperity tips and an isosceles trapezoid textured surface. Results: Average friction forces for the different tips are presented, and the friction processes are analyzed. A stable friction process is discovered for a specific case, and the average friction force is kept at two stable values corresponding to two sliding directions. Conclusion: Compared with the total average friction forces of a smooth surface, the textured surface can reduce the friction forces greatly. This work could contribute to the textured surface design to improve frictional properties in the space environment.

A review of treatment plans for the biological clock of astronauts: A systematic review

Since the start of civilization and even further back, humankind has been dreaming of flying. Recently, this dream has come true and reached beyond that and sends astronauts to outer space. However, by achieving this milestone, we encountered new problems that were new to humanity. One of the biggest problems is having a sleeping disorder and disruption of the biological clock. It is essential because having a sleep disorder makes astronauts unable to function at 100% capacity, and in outer space, it is dangerous. Some treatments for sleep disorders include drug therapy, such as Dexedrine, temazepam, modafinil, bupropion, melatonin, zolpidem, dextroamphetamine, light treatment, or a trickling sleep/wake schedule, according to NASA's guidelines. This study aimed to review the treatments for sleep disorders and disruption of the biological clock aimed at astronauts during space flights. We presented the different treatments and discussed and oriented the next prospect of research on sleep in space. Therefore, there will be guidelines for astronauts during their flights. Since the beginning of space travel, there have been many papers regarding space and weightlessness on the adverse effects on health. Studies have described the effect of space travel and the environment of microgravity on health. A few studies include both the short- and long-term effects of microgravity on the biological clock. With this new dawn and sending new astronauts to International Space Station (ISS) with NASA and SpaceX commercial Falcon 9 rocket, which opened a new horizon for spaceflights, it is even more important to consider the adverse effects microgravity on health. Purpose: This review aims to specifically analyze the biological clock, sleep deficiency, and circadian disorders. As we acknowledge, there is a sleep deficiency associated with complex microgravity environs and space missions before and after launch. Material and methods: Two researchers searched a thorough and detailed search of the PubMed database with the keywords mentioned below. The search was performed in November 2020 without any time limitations. We only included human studies and articles in the English language. Results: A total of 148 articles were found, and after going through titles, 77 articles were chosen for checking abstracts. Finally, only 12 manuscripts were accepted for data extraction. Conclusion: It is essential for health care involved in space travel providers to help pre-emptively identify problems that may prevent severe consequences during a microgravity environment. Sleep and circadian factors are the fundamental issues of human fatigue, and aviation schedules significantly impact both. We should admire a computerized fatigue model for having a better approach to studying the impact of scheduling.

A NEW ANALYTICAL MODELING FOR FRACTAL BLASIUS EQUATION IN MICROGRAVITY SPACE

In this paper, the fractal derivative is employed to define the fractal Blasius equation in a microgravity space arising in fluid dynamics, and its fractal variational principle is successfully established by the fractal semi-inverse transform method. The approximate analytical solution of the fractal Blasius equation is obtained by the variational iteration method. Our results have theoretical significance and practical application value. The example shows the approximate approach is reliable and accurate.

Uncovering Transcriptional Responses to Fractional Gravity in Arabidopsis Roots.

Although many reports characterize the transcriptional response of Arabidopsis seedlings to microgravity, few investigate the effect of partial or fractional gravity on gene expression. Understanding plant responses to fractional gravity is relevant for plant growth on lunar and Martian surfaces. The plant signaling flight experiment utilized the European Modular Cultivation System (EMCS) onboard the International Space Station (ISS). The EMCS consisted of two rotors within a controlled chamber allowing for two experimental conditions, microgravity (stationary rotor) and simulated gravity in space. Seedlings were grown for 5 days under continuous light in seed cassettes. The arrangement of the seed cassettes within each experimental container results in a gradient of fractional g (in the spinning rotor). To investigate whether gene expression patterns are sensitive to fractional g, we carried out transcriptional profiling of root samples exposed to microgravity or partial g (ranging from 0.53 to 0.88 g). Data were analyzed using DESeq2 with fractional g as a continuous variable in the design model in order to query gene expression across the gravity continuum. We identified a subset of genes whose expression correlates with changes in fractional g. Interestingly, the most responsive genes include those encoding transcription factors, defense, and cell wall-related proteins and heat shock proteins.