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GRAVITY VECTOR VARIATION AFFECTS CYTOSKELETAL ORGANIZATION OF ENDOTHELIAL CELLS.  A. Higashibata¹,  M. Imamizo-Sato² and N. Ishioka¹.  ¹Space Utilization Research Center, Space Utilization System, National Space Development Agency of Japan, ²Space Development Division, Advanced Engineering Services Co., Ltd, Tsukuba, Ibaraki, JAPAN. 

   The effect of microgravity environment on cellular events has been observed in past space experiments, but the gravity-sense mechanism of cells is unclear.  The goals of our study are to define the signaling pathway of gravity-sense and to reveal the gravity sensor in cells.  We have investigated morphologically the cytoskeletal changes of endothelial cells cultured under clinorotated condition. Under that condition, microtubule organizing centers were poorly defined, and the clusters of MAP2 (microtubule associate protein 2) were not observed.  Furthermore, RhoA, small G protein, was widely located in clinorotated cells, but the organizing of actin stress fiber was not promoted compared with those of static cultured.  These results indicated that gravity vector variation affects the cytoskeleton organizing in cells, especially signaling pathway that is related to Rho protein.  The results of mRNA level analysis support those morphological data.  The images of differential display showed that gene expression level of cytoskeletal proteins and of cell-adhesion proteins responded to gravity vector variation.