Skeletal muscle is a major organ involved in the homeostasis of glucose and lipid metabolism. Here, we report that a muscle-derived secretory protein, attractin, highly expressed under unloading conditions, could regulate the expression of uncoupling protein-2 (UCP-2), which is a proton carrier that uncouples electron transport from ATP synthesis, in adipocytes. Attractin has two alternative splicing variants: membrane-bound and secreted forms. Since loss-of-function mutations in membrane-bound attractin decreases body weight by suppressing appetite in mice, we hypothesize that secreted-type attractin also could regulate energy homeostasis. We first showed that unloading conditions, such as spaceflight and tail-suspension, increased the amount of secreted-type attractin mRNA in rat gastrocnemius muscle. Next, co-culturing of attractin-overexpressing COS7 cells with 3T3-L1 adipocytes or L6 myotubes revealed that secreted-type attractin increased the amounts of UCP-2 mRNA and protein in 3T3-L1 adipocytes, but not in L6 myotubes. Secreted-type attractin failed to upregulate expression of UCP-1 and UCP-3 in 3T3-L1 adipocytes. Two-dimensional polyacrylamide gel electrophoresis also showed that expression of several proteins were up- or down-regulated in 3T3-L1 adipocytes co-cultured with attractin-overexpressing COS7 cells, whereas the profile of protein expression hardly changed in the co-cultured L6 myotubes, indicating that secreted-type attractin preferentially affects adipocytes more than myotubes. Our present study suggests that secreted-type attractin may function as an energy regulating factor in skeletal muscle by upregulating UCP-2 expression level in adipocytes.

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To investigate the effects of hypergravity on the pituitary gland and the target organs of amphibians, we raised frogs, Xenopus laevis under hypergravity environment (2 and 5G) environments from fertilization to the beginning of metamorphosis (St 57) and completion of metamorphosis (St 66). The frogs developed at 2G and 5G, but they were smaller than those raised at 1G. Moreover, the development of the frogs was delayed under both hypergravity conditions. The total volume, cell size and cell number of the pituitary of hypergravity-treated frogs were reduced. In the treated thyroid, the total volume and height of the epithelium were also reduced. Cell size was reduced in the adrenal grand of treated frogs. These morphological changes of the pituitary-target organs indicate that hypergravity alters their endocrinological functions. These results suggest that gravity different from the terrestrial environment causes dysfunction and hypofunction in the endocrine systems, and that the organisms may not be able to maintain their inherent life cycles under such conditions.

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Gravitaxis of swimming microorganisms has so far been explained largely in terms of the physical properties of the microorganisms that are assumed not to have any speculative mechanisms of gravity sensation. However gravity-induced sensory input and the subsequent modulation of locomotor activity in Paramecium has been suggested by precise analyses of swimming velocity as a function of swimming direction with respect to gravity. Paramecium appears to modulate its propulsive effort depending on the swimming direction by increasing the propulsive speed in upward and decreasing it in downward directions. This response termed as gravikinesis was obtained from the averaged measurement on a large number of the cell. In the present study we aimed to confirm the results on the basis of the measurement on the swimming of a single cell. Velocities of upward and downward swimming was measured from each single cell, and the velocity of sinking was measured on the same cell which was immobilized by Ni²⁺. We confirmed the gravikinesis from the analysis on the swimming of single cells. In addition, we found that in the hyper-density medium containing Percoll cells showed opposite gravikinesis to that in the hypo-density medium. These results may suggest the mechanosensitivity of the cell membrane as a physiological sensor underlying the gravity-dependent response in Paramecium.

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Concept of space agriculture is developed for habitation on Mars. Space diet is designed and evaluated with nutritional point of view. Combination of rice, soybean, sweet potato, green-yellow vegetable (represented by Komatsuna), silkworm pupa, and loach was found to fill the nutritional requirements.

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