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The Differentiation of Myoblast is Regulated by Gravity.  Y. Kawahara^1,2, R. Yoshimoto¹, A. Sasaki¹, S.L. Wu¹, T. Manabe¹, T. Kajiume³, M. Takeda³, T. Magaki³, and L. Yuge^1,2; ¹Graduate School of Health Sciences, ²Space Bio-Laboratories Y. K., and ³Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan. 

   A 3D-clinostat is a multi-directional gravity device, by controlled rotation of two axes, and makes 10^-3 G average over time. We previously reported that microgravity inhibited stem cell and bone marrow-derived cell differentiation. In the present study, the effects of microgravity on myoblast differentiation were examined. L6 rat myoblast cells were seeded in OptiCell and propagated in normal 1G environment. When L6 cells reached confluence on culture day 4, they were induced differentiation and then exposed to 10^-3G environment (group CL). Control cells were cultured in normal 1G environment (group C). After 5days induced differentiation, cells were divided into two more groups and cultured for another 5 days. One was continued to culture in same environment (group CL/CL or group C/C), the other was exchanged culture environment of the cells (group CL/C or group C/CL), thus cells in group CL were transferred to 1G, and cells in group C were transferred to 10^-3G. It was shown that microgravity inhibited myoblast differentiation by morphological observation and molecular biological analysis. Moreover, the cells in group CL/C began differentiation when cells put in 1G environment, while the cells in group C/CL stopped differentiation when cells put in 10^-3G environment. Here we show that gravity has possible effects on myoblast differentiation.