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influence  of 2g hypergravity on embryonic gene expression.  L. Ma and P. McCaffery.   Dept Cell Biology, UMMS/E.K. Shriver Center, Waltham, MA.  

   This study investigated the influence of gravity on the developing embryo, employing the 24-foot centrifuge at NASA-Ames to simulate 2G hypergravity. The focus was on a mid-gestational window between embryonic days 10-14, starting centrifugation at embryonic day 4.  As we have presented previously, this initially results in a reduction in growth evident at embryonic day 10 relative to control.  However, between embryonic day 10 and 14 growth is accelerated so that by the end of this period the size of the embryo is nearly normal.  This phase of increased growth is not accompanied by a generalized increase in gene expression.  However certain key developmental genes involved in development change in the brain are induced.  Sonic hedgehog (shh), a gene that promotes cell differentiation, patterning, survival and proliferation, increased substantially along the midline of the hindbrain at embryonic days 10 and 12.  A second key developmental gene required for growth and differentiation, RAR beta, exhibited a slightly later latency than shh, and increased at embryonic days 12 and 14. Whether the activation of these genes is “cause or effect” in relationship to the increase in growth cannot be determined from these results but the position of these genes as key regulators of multiple downstream effectors of growth suggest that they are early determinants of increased growth of the embryo.

(Supported by NASA: NAG2-1438 and NIH: H05515)