Mechanical culture conditions effect gene expression: gravity-induced changes on the space shuttle.

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Three-dimensional suspension culture is a gravity-limited phenomenon. The balancing forces necessary to keep the aggregates in suspension increase directly with aggregate size. This leads to a self-propagating cycle of cell damage by balancing forces. Cell culture in microgravity avoids this trade-off. We determined which genes mediate three-dimensional culture of cell and tissue aggregates in the low-shear stress, low-turbulent environment of actual microgravity. Primary cultures of human renal cortical cells were flown on the space shuttle. Cells grown in microgravity and ground-based controls were grown for 6 days and fixed. RNA was extracted, and automated gene array analysis of the expression of 10, 000 genes was performed. A select group of genes were regulated in microgravity. These 1,632 genes were independent of known shear stress response element-dependent genes and heat shock proteins. Specific transcription factors underwent large changes in microgravity including the Wilms' tumor zinc finger protein, and the vitamin D receptor. A specific group of genes, under the control of defined transcription factors, mediate three-dimensional suspension culture under microgravity conditions.