Testes and duct deferens of mice during space flight: cytoskeleton structure, sperm-specific proteins and epigenetic events

Mission SpaceX CRS-19 RRRM-1 space flight induced skin genomic plasticity via an epigenetic trigger

Genomic plasticity helps adapt to extreme environmental conditions. We tested the hypothesis that exposure to space environment (ESE) impacts the epigenome inducing genomic plasticity. Murine skin samples from the Rodent Research Reference Mission-1 were procured from the International Space Station (ISS) National Laboratory. Targeted RNA sequencing to test differential gene expression between the skin of ESE versus ground controls revealed upregulation of VEGF-mediated angiogenesis pathways secondary to promoter hypomethylation in responders. Methylome sequencing identified ESE-sensitive hypomethylated genes including developmental angiogenic genes Araf, Vegfb, and Vegfr1. Based on differentially expressed genes, the angiogenesis biofunction was enriched in responders. The induction of genomic plasticity in response to ESE, as reported herein, may be viewed as a mark of biological resilience that is evident in a minority of organisms, responders but not in non-responders, exposed to the same stressor. Inducible genomic plasticity may be implicated in natural resilience to ESE.

The Motility of Mouse Spermatozoa Changes Differentially After 30-Minute Exposure Under Simulating Weightlessness and Hypergravity

Research into the mechanisms by which gravity influences spermatozoa has implications for maintaining the species in deep space exploration and may provide new approaches to reproductive technologies on Earth. Changes in the speed of mouse spermatozoa after 30 min exposure to simulated weightlessness (by 3D-clinostat) and 2 g hypergravity (by centrifugation) were studied using inhibitory analysis. Simulated microgravity after 30 min led to an increase in the speed of spermatozoa and against the background of an increase in the relative calcium content in the cytoplasm. This effect was prevented by the introduction of 6-(dimethylamino) purine, wortmannin, and calyculin A. Hypergravity led to a decrease in the speed of spermatozoa movement, which was prevented by sodium orthovanadate and calyculin A. At the same time, under microgravity conditions, there was a redistribution of proteins forming microfilament bundles between the membrane and cytoplasmic compartments and under hypergravity conditions-proteins forming networks. The obtained results indicate that even a short exposure of spermatozoa to altered gravity leads to the launch of mechanotransduction pathways in them and a change in motility.

Single Cell in a Gravity Field

The exploration of deep space or other bodies of the solar system, associated with a long stay in microgravity or altered gravity, requires the development of fundamentally new methods of protecting the human body. Most of the negative changes in micro- or hypergravity occur at the cellular level; however, the mechanism of reception of the altered gravity and transduction of this signal, leading to the formation of an adaptive pattern of the cell, is still poorly understood. At the same time, most of the negative changes that occur in early embryos when the force of gravity changes almost disappear by the time the new organism is born. This review is devoted to the responses of early embryos and stem cells, as well as terminally differentiated germ cells, to changes in gravity. An attempt was made to generalize the data presented in the literature and propose a possible unified mechanism for the reception by a single cell of an increase and decrease in gravity based on various deformations of the cortical cytoskeleton.

Sperm of Fruit Fly Drosophila melanogaster under Space Flight

Studies of reproductive function under long-term space flight conditions are of interest in planning the exploration of deep space. Motility, including the use of various inhibitors, cellular respiration, and the content of cytoskeletal proteins were studied, assessing the level of expression of the corresponding genes in spermatozoa of Drosophila melanogaster, which were in space flight conditions for 12 days. The experiment was carried out twice on board the Russian Segment of the International Space Station. Sperm motility speed after space flight, and subsequently 16 h after landing, is reduced relative to the control by 20% (p < 0.05). In comparison with the simulation experiment, we showed that this occurs as a result of the action of overloads and readaptation to the Earth’s gravity. At the same time, cellular respiration, the content of proteins of the respiratory chain, and the expression of their genes do not change. We used kinase inhibitor 6-(dimethylamino)purine (6-DMAP) and phosphatase inhibitors; 6-DMAP restored the reduced the speed of spermatozoa in the flight group to that of the control. These results can be useful in developing a strategy for protecting reproductive health during the development of other bodies in the solar system.

Mitochondrial Respiration in Drosophila Ovaries after a Full Cycle of Oogenesis under Simulated Microgravity

Studies of the function of the female reproductive system in zero gravity are urgent for the future exploration of deep space. Female reproductive cells, oocytes, are rich in mitochondria, which allow oocytes to produce embryos. The rate of cellular respiration was determined to assess the functional state of the mitochondrial apparatus in Drosophila melanogaster ovaries in which the full cycle of oogenesis took place under simulated microgravity. Since cellular respiration depends on the state of the cytoskeleton, the contents of the main cytoskeletal proteins were determined by Western blotting. To modulate the structure of the cytoskeleton, essential phospholipids were administered per os at a dosage of 500 mg/kg in medium. The results of this study show that after a full cycle of oogenesis under simulated microgravity, the rate of cellular respiration in the fruit fly ovaries increases, apparently due to complex II of the respiratory chain. At the same time, we did not find any changes in the area of oocytes or in the content of proteins in the respiratory chain. However, changes were found in the relative contents of proteins of the actin cytoskeleton. There were no changes of essential phospholipids and no increase in the rate of cellular respiration of the ovaries after exposure to simulated microgravity. However, in the control, the administration of essential phospholipids led to a decrease in the efficiency of oxygen consumption in the flies’ ovaries due to complexes IV–V.

Drosophila melanogaster Sperm under Simulated Microgravity and a Hypomagnetic Field: Motility and Cell Respiration

The role of the Earth's gravitational and magnetic fields in the evolution and maintenance of normal processes of various animal species remains unclear. The aim of this work was to determine the effect of simulated microgravity and hypomagnetic conditions for 1, 3, and 6 h on the sperm motility of the fruit fly Drosophila melanogaster. In addition to the usual diet, the groups were administered oral essential phospholipids at a dosage of 500 mg/kg in medium. The speed of the sperm tails was determined by video recording and analysis of the obtained video files, protein content by western blotting, and cell respiration by polarography. The results indicated an increase in the speed of movement of the sperm tails after 6 h in simulated microgravity. The levels of proteins that form the axoneme of the sperm tail did not change, but cellular respiration was altered. A similar effect occurred with the administration of essential phospholipids. These results may be due to a change in the level of phosphorylation of motor proteins. Exposure to hypomagnetic conditions led to a decrease in motility after 6 h against a background of a decrease in the rate of cellular respiration due to complex I of the respiratory chain. This effect was not observed in the flies that received essential phospholipids. However, after 1 h under hypomagnetic conditions, the rate of cellular respiration also increased due to complex I, including that in the sperm of flies receiving essential phospholipids.

Wheat Space Odyssey: "From Seed to Seed". Kernel Morphology

The long-term autonomous existence of man in extraterrestrial conditions is associated with the need to cultivate plants-the only affordable and effective means for both providing oxygen and CO2 utilization, and providing one of the most habitual and energetically valuable products: plant food. In this study, we analyzed the results of the space odyssey of wheat and compared the morphological features of parental grains harvested from soil grown wheat plants, the grains obtained from plants grown in a specialized device for plant cultivation-the "Lada" space greenhouses during space flight in the ISS, and the grains obtained from plants in the same device on Earth. The seeds obtained under various conditions were studied using scanning electron microscopy. We studied the mutual location of the surface layers of the kernel cover tissues, the structural features of the tube and cross cells of the fruit coat (pericarp), and the birsh hairs of the kernels. It was found that the grains obtained under wheat plants cultivation on board of the ISS in near space had some specific differences from the parental, original grains, and the grains obtained from plants grown in the "Lada" greenhouse in ground conditions. These changes were manifested in a shortening of the birsh hairs, and a change in the size and relative arrangement of the cells of the kernel coat. We suggest that such changes are a manifestation of the sensitivity of the cytoskeleton reorganization systems and water exchange to the influence of particular physical conditions of space flight (microgravity, increased doses of radiation, etc.). Thus, the revealed changes did not hinder the wheat grains production "from seed to seed", which allows the cultivation of this crop in stable life support systems in near earth orbit.

Guest Edited Collection: Gravitational biology and space medicine

A return to the Moon, Mars expeditions, and a rise in space tourism will lead to an increasing number of human spaceflights. The ‘Gravitational biology and space medicine’ Collection focuses on the challenges to the health of humans in space during long-term space missions and the physiological changes during short-term altered gravity conditions, the possible influence of space radiation, available countermeasures and possible applications on Earth. In addition, studies reporting on in vivo changes in space-flown mice were published. Finally, this Collection also brings together articles reporting experiments using cells cultured under conditions of real microgravity on the International Space Station, or exposed in ground-based facilities, in order to study morphological and molecular alterations in different cell types.

Male mice, caged in the International Space Station for 35 days, sire healthy offspring

The effect on the reproductive system and fertility of living in a space environment remains unclear. Here, we caged 12 male mice under artificial gravity (≈1 gravity) (AG) or microgravity (MG) in the International Space Station (ISS) for 35 days, and characterized the male reproductive organs (testes, epididymides, and accessory glands) after their return to earth. Mice caged on earth during the 35 days served as a “ground” control (GC). Only a decrease in accessory gland weight was detected in AG and MG males; however, none of the reproductive organs showed any overt microscopic defects or changes in gene expression as determined by RNA-seq. The cauda epididymal spermatozoa from AG and MG mice could fertilize oocytes in vitro at comparable levels as GC males. When the fertilized eggs were transferred into pseudo-pregnant females, there was no significant difference in pups delivered (pups/transferred eggs) among GC, AG, and MG spermatozoa. In addition, the growth rates and fecundity of the obtained pups were comparable among all groups. We conclude that short-term stays in outer space do not cause overt defects in the physiological function of male reproductive organs, sperm function, and offspring viability.