Finally, the report concluded that investigations involving single cells and cell culture models should be analyzed in ground-based studies.

The Strategy report (NRC, 1998) also reviewed the current state of the field of developmental biology and the potential for meaningful investigations of development processes in microgravity. It stressed two main questions relevant to future investigations conducted in space: Can organisms undergo normal development in microgravity? Are there developmental phenomena that can be studied better in microgravity than on Earth? It was concluded that the space environment may indeed be useful for understanding certain biological phenomena in developing systems. Specific systems in which gravity was considered likely to play a critical role in development and/or maintenance include the vestibular system and the multiple sensory systems that interact with the vestibular system. The answers to these questions could have profound effects on the performance of astronauts in space and their postflight recovery on Earth. Gravity was also expected to influence topographical neural space maps that exist throughout the brain, with attendant effects on neuroplasticity, i.e., long-term changes in neuron structure and function in response to changes in their activity. Finally, the report concluded that analyses of complete life cycles in space could determine if some developmental events are affected by reduced gravity, and that high priority should be given to testing vertebrate models, including avian systems. If developmental effects are detected, control experiments must be performed on the ground and in space with the latter, including the use of a space-based 1-g centrifuge. Important issues related to these goals should be investigated in ground-based studies as preludes for investigation in space. Controls for the effect of non-gravitational stresses likely to be encountered in space, such as loud noise and vibration, must also be performed on the ground so that space experiments can be designed to isolate the effects of microgravity from the effects of other stresses.

A number of experiments under way within current NASA fundamental biology and biotechnology programs in cell and developmental biology are asking questions pertinent to the recommendations made in the Strategy report (NRC, 1998). An examination of the NASA task book relevant to fundamental biology (NASA, 2001c) found 102 entries, nearly all of them ground-based studies. Emphasis is being placed on the development and function of the vestibular system, otoliths and hair cells, bone, smooth and skeletal muscle, adrenal cells, endothelial cells, and lymphocytes. Studies are under way in the areas of proprioreception, hormone response, signal transduction, immune response, neuronal development and plasticity, early embryonic development and stem cell migration, aging, neurosecretion, cytoskeleton and motility, cell survival, circadian rhythms, and homeostasis and energy metabolism. Some use is being made of “simpler” eukaryotic, multicellular organisms such as fruit flies and zebra fish, as well as unicellular prokaryotes. Overall, these studies stress the potential importance of cell and developmental biology for both basic research and countermeasure research in bioastronautics.

Note that the assessment in the next subsection largely ignores the cell and developmental biology of plant systems, which are discussed in a separate section.

Impact of ISS Changes

In terms of cell and developmental biology research, the critical resources of the Rev. F configuration included a crew of six or seven members, habitat holding racks for mice and rats (including special inserts for animal biotelemetry systems), a 2.5-m, 1-g centrifuge, a life sciences glove box, a cryofreezer, an insect habitat, an aquatic habitat, an avian research facility, an avian development facility, and a budget commensurate with the needs of world-class cell and developmental biology research.

A number of these critical resources have been considerably delayed or eliminated (Liskowski, 2002a). For example, the advanced animal habitat has been eliminated along with the avian research facility, essentially precluding the ability to characterize the genetic and developmental response of nonhuman vertebrates such as rats and mice to long-term exposure to space. Deployment of the centrifuge accommodation module and the 2.5-m, 1-g centrifuge and associated software (by NASDA), a critical element of control experiment design, has been delayed until at least 2008. Other facilities are



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