With the increased availability of research opportunities on the ISS and the new hardware developed, further investigation of these processes will clarify how cells behave in microgravity. A better understanding of how the cells in the physiological systems, such as muscle, bone, balance, and cardiovascular, sense and respond to microgravity would have immediate relevance for the manned space program.

Potential research topics would not be limited to areas that have already been explored, but could come in other areas, including the adaptive responses of cells in microgravity to factors such as: (a) radiation; (b) induced phenotypic and genotypic changes; (c) effect of the space environment on replicating cells; (d) and the effect of microgravity on plant cells and tissues, on microorganisms that cause disease or that will be used for waste treatment on long-duration flights, and on cells (e.g., osteoblasts) that may not proliferate in bioreactors as they are currently designed (Unworth and Lelkes 1998).

As mentioned above, the key areas in which perturbations of cell structure and function in microgravity are observed are components of nuclear architecture, cytoarchitecture, and the extracellular matrix. It is becoming increasingly evident that the organization of genes and regulatory proteins within the nucleus, the organization of nucleic acids and signaling proteins in the cytoplasm and cytoskeleton, and the organization of regulatory macromolecules within the extracellular matrix contribute to the physiologically responsive fidelity of gene expression. Consequently, the functional interrelationships between cell structure and gene expression within the three-dimensional context of cell and tissue organization can be rigorously and systematically studied under microgravity and regular Earth-gravity conditions. The corollary is that microgravity can provide valuable insight into structure-function interrelationships that connect control of gene expression to cell and tissue architecture (National Research Council 1998).

The microgravity environment has shown a unique utility to facilitate cultures of virus and pathogens. Examples of flown viruses include the Norwallc virus, a gastroeneric pathogen, the influenza flu virus, and the respiratory syncytial virus that causes pneumonia and severe upper respiratory infection. Specimens derived from the space-grown virus can be injected in selected cell lines obtained from tissue culture differentiation studies, and the infected cell cultures are characterized for evidence of virus replication. The ultimate phase is to generate these adapted strains of the virus with enhanced replication properties in conventional tissue culture lines and systems.

Another technique is to better determine the atomic structure of the antibody by growing crystals of the virus's antibody (see section on crystal growth below). Knowing the structure of the antibody will accelerate the development of an effective vaccine against the virus. Thus, microgravity, as an experimental tool, may provide insight into fundamental aspects of biological regulation that will be important in the space as well as terrestrial environment (Volkman et al. 1995, Kaysen et al. 1999).

Figure 8-04. On board the ISS, ESA astronaut Pedro Duque of Spain watches a water bubble floating between him and the camera, showing his reflection (reversed). Photo courtesv of 'NASA.
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