Teleost fish live under a constant force derived from gravity, with hard tissues playing important roles to help maintain body balance. However, the mechanism of hard tissue formation induced by gravity remains unclear. To examine the effects of gravity in aquatic animals, we performed experiments with medaka fish reared in a hypergravity environment, in which the force of gravity exceeded that present on the surface of the Earth, and analyzed hard tissue formation. Medaka fish were reared for 6 months under a normal gravitational force (1G) or that 5.29 times greater than normal (5.29G) using a centrifuge designated for small fish rearing. Micro-CT analysis results showed that hypergravity induced a vertebral curvature towards the dorsal side and asymmetric formation of otoliths in which the cross-sectional area was increased. Our findings indicate that the process of adaptation to a hypergravity environment results in spinal and otolith deformation in medaka fish.
This paper presents a processing machine for aerogel returned to the earth after one year exposure to space at international space station. To support the astrobiology mission by processing returned sample into suitable-sized chips for biological/chemical analysis, CLOXS (Captured particles Locating, Observation and eXtracting System) was fabricated for the extraction of triangular prism-shaped chips (=Yokans) that contained collision tracks of particles that were captured in space. A novel needle was fabricated, and was mounted on the machine to cut the sides of Yokan by repeated poking motions. Typical Yokans were chosen for the processed sides roughness evaluation, and the standard deviations of the displacement were no larger than 159 μm, which was satisfactory by the use of 200-300 μm diameter needle.
We examined the effects of hypergravity on nuclear positioning in epidermal cells of azuki bean (Vigna angularis) epicotyls. The nucleus was positioned almost in the center of the cell under 1 G conditions. When the epicotyls were exposed to basipetal hypergravity by centrifugation, the nucleus was displaced toward the centrifugal side of the cell in a linear dose-response manner. The nuclear displacement started within 20 min by exposure to basipetal hypergravity at 300 G, and reached ca. 35% from the centrifugal edge of the cell after 2 h. The displaced nucleus recentered by removal of hypergravity stimuli. The nucleus was also displaced by acropetal hypergravity at the similar degree as basipetal hypergravity. The displacement by hypergravity of the nucleus was stimulated, when actin filaments were disrupted by cytochalasin D treatment. These results suggest that the positioning of the nucleus in epidermal cells is maintained by actin filaments, which is affected by gravity in azuki bean epicotyls.