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.

Sperm Motility of Mice under Simulated Microgravity and Hypergravity.

For deep space exploration, reproductive health must be maintained to preserve the species. However, the mechanisms underlying the effect of changes in gravity on male germ cells remain poorly understood. The aim of this study was to determine the effect of simulated micro- and hypergravity on mouse sperm motility and the mechanisms of this change. For 1, 3 and 6 h, mouse sperm samples isolated from the caudal epididymis were subjected to simulated microgravity using a random position machine and 2g hypergravity using a centrifuge. The experimental samples were compared with static and dynamic controls. The sperm motility and the percentage of motile sperm were determined using microscopy and video analysis, cell respiration was determined by polarography, the protein content was assessed by Western blotting and the mRNA levels were determined using qRT-PCR. The results indicated that hypergravity conditions led to more significant changes than simulated microgravity conditions: after 1 h, the speed of sperm movement decreased, and after 3 h, the number of motile cells began to decrease. Under the microgravity model, the speed of movement did not change, but the motile spermatozoa decreased after 6 h of exposure. These changes are likely associated with a change in the structure of the microtubule cytoskeleton, and changes in the energy supply are an adaptive reaction to changes in sperm motility.

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

To analyze the effect of gravity on the structure of germinal tissues, we examined tissues of the testes and duct deferens of mice that were exposed to space flight conditions for 21-24 days (experiment Rodent Research-4, SpaceX-10 mission, February 2017, USA). We evaluated the levels of cytoskeletal proteins, sperm-specific proteins, and epigenetic events; in particular, we evaluated levels of 5-hydroxymethylcytosine and of enzymes that regulate DNA methylation/demethylation. We did not detect changes in the levels of cytoskeletal proteins, sperm-specific proteins, DNA-methylases, DNA demethylases, DNA acetylases, or histone deacetylases. However, there were changes at the gene expression level. In particular, there was an increase in the demethylase Tet2 and a decrease in the histone deacetylase Hdac1. These gene expression changes may be of key importance during the early period of readaptation since they could lead to an increase in the expression of target genes.