The random positioning machine (RPM) is a method used to generate a simulated-microgravity environment at approximately 0 g. Using an RPM, we analyzed the global gene expression of A8 cells derived from the liver of adult Xenopus laevis. A range of genes on a Xenopus 44K-scale microarray were up- or downregulated two-fold or more: 43 genes (up, 36 genes; down, 7 genes) on culture day 5 in RPM, 74 genes (up, 48 genes; down, 26 genes) on day 8, 105 genes (up, 71 genes; down, 34 genes) on day 10, and 132 genes (up, 98 genes; down, 34 genes) on day 15. Five genes were upregulated two-fold or more throughout culturing in RPM, while only one gene was downregulated over the entire time. We then compared the expression patterns of the RPM-dependent genes in the A8 cells with those in A6 cells established from the kidney of adult Xenopus laevis. Six upregulated genes and three downregulated genes showed the same expression patterns throughout the culturing of A6 and A8 cells in RPM. Such globally responsive genes may play a common role in the cell response to simulated microgravity. We were particularly interested in the downregulation of SPARC in both cell types in RPM, which supported previous observations from simulated-microgravity experiments on earth or microgravity in space. We conclude that SPARC is plays a key role in the response of a cell to microgravity.
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