Akira Higashibata

It is important for human life in space to study the effects of environmental factors during spaceflight on a number of physiological phenomena. In the ICE-first experiment (International Caenorhabditis elegans Experiment-1, Mission DELTA, April 2004), we found that (1) both pachytene-checkpoint apoptosis and physiological apoptosis in germ cells occurred normally under spaceflight conditions and (2) certain genes related to signaling pathway of G-protein coupled receptor protein and to locomotory behavior tended to decrease in the spaceflown C. elegans. (3) In the hypergravity condition, we determined that the most susceptible aspect in the life cycle of this organism is the oocyte meiotic division for exclusion of polar bodies and the anterior-posterior polarization shortly after fertilization. (4) We also found several genes specifically responding to environmental stresses such as radiation by transcriptome analyses of entire genome using DNA microarray in several mutants and RNA interference (RNAi) animals. Since these phenomena and the identified genes are highly conserved in mammalian systems, the model experiments using this organism are useful to study the effects of space environment on human life. We are now attempting to study the RNAi effect, signal transduction, adaptation and evolution responding to space environment in future space experiments using the nematode C. elegans.

In the present study,we hypothesize that Cbl-b mediated ubiquitination plays an important role of atrophy during spaceflight. To examine our hypothesis, we proposed and designed a flight experiment. In this section, we report that the result of studies 1) confirmation of the method of RNA extraction from flight samples,2) analysis of Cbl-b gene expression under oxidative stress or simulated microgravity, 3) Cbl-b has a important function in bone atrophy mechanism not only mucle atrophy.

In previous space flight experiments, the effects of microgravity on living organism were observed. The molecular mechanisms of microgravity effect, however, have not been cleared. In order to elucidate the detail of the gravity sense and response mechanisms on life, we focused the three topics as follows: 1) the transferring mechanisms of mechano-stress into innercellular signal in osteoblast cells, 2) cytoskeleton and small G proteins involved in gravity sense and response in endothelial cells, 3) proteomic approaches of gravitropic-related molecules in higher plants.In each topic, we could find that the common signal pathways functioned as gravity response in various species. We could advance greatly the studies how gravity signals were transferred into biochemical reactions and what molecules are important on the transferring process.