Avian

Birds share extensive homology with mammals at the cell, tissue and molecular level. Developmental patterns of many genes are known, a genome project is proceeding, and some mutants are available. They have short developmental cycles (21 days for chick, 16 days for quail), though with relatively long life cycles. Avian species can be studied in large numbers and early embryos can be stored at cool temperatures and subsequently re-warmed to in order to restart development at desired times.

Gravity also affects the early stages of development in birds. In the oviduct, the fertilized egg is subjected to repeated rotations. Numerous experiments have shown that the direction of this rotation and the position of the egg relative to the vertical will determine the orientation of the embryo's bilateral plane of symmetry (Planel and Oser 1984).

Preliminary results indicate no adverse effects of vibration and g force (at least those experienced during a Space Shuttle launch) on avian development. Flight data on early embryogenesis exist as well, indicating that there are some sensitive periods during which these embryos do not do well in the flight environment. To date, only few quail embryos have survived in weightlessness and only two of these embryos survived to the latter stages of development, i.e., to the 16th days of incubation. These flight experiments could indicate that gravity may be needed during the earliest stages of avian embryogenesis, but is not important for the latter stages of development (Bellairs 1993).

However, interpretations of the results were made more difficult by the fact the synchronous control showed a similar lack of viability. Retrospective analysis of onboard flight recording data suggests that the incubator temperature control malfunctioned and the eggs were being incubated at 42°C instead of the programmed 37.5°C. Also, an egg incubator within a centrifuge can allow determining if lack of gravity is the reason for the death of young avian embryos in space.

On future spaceflights experiments will attempt to determine the effect of weightlessness on embryonic development initiated after the launch, the fecundity of adult quail during orbit, and the assessment of their hormones and reproductive tissues after orbit. Other objectives include the regeneration potential of quail in weightlessness based on primordial germ cell migration and differentiation, gametogenesis, ovulation, fertilization, embryonic development, and hatching.

Figure 2-13. Japanese quail chick on board the Russian space station Mir. Quail eggs that underwent two thirds of embryonic development on Earth were incubated. They hatched during the spaceflight and were returned back to Earth for postflight analysis.

Figure 2-13. Japanese quail chick on board the Russian space station Mir. Quail eggs that underwent two thirds of embryonic development on Earth were incubated. They hatched during the spaceflight and were returned back to Earth for postflight analysis.

These experiments will provide substantial basic information about the effects of weightlessness on embryonic differentiation and development, as well as important information about adult avian endocrinology and physiology. Other experiments will investigate the acute response of birds to the absence of microgravity. One predictable and commonly observed response of animals that find themselves in microgravity is to react as if they were upside-down, and they begins to roll over and over to "right" them up. It is still unknown if birds will be disoriented or will quickly lean to fly in microgravity (Figure 2-13).

Figure 2-14. Astronaut Shannon Lucid checks on wheat plants on board the Russian Mir space station. Photo courtesy of NASA.

5 CONCLUSION

Model organisms are being used to investigate some of the most up-to-date areas in biological research. Each model organism is distinctively suited as a simplified model to the study of complex aspects of biology. Researchers are repeatedly surprised that discoveries in simple organisms are relevant to human biology, which encourages transposition of results from one model system to another, and highlighting the extent of conservation and commonality of life forms. The differences hold value as well, as they provide important insights to understanding cell physiology and pathology (Blair Hedges 2002).

Animal and plant model organisms have proven particularly useful for space biology, because of their advantages for experimental research, such as rapid development with short life cycles, small adult size, ready availability, and because of the large number of ground-based studies carried out on them.

A large amount of genetic information can then be derived from these organisms, providing valuable data for the analysis of normal human development and gene regulation, genetic diseases, and evolutionary processes. It is now known that microgravity induces certain physiological changes that may produce useful experimental models for studies of Earth-based diseases such as osteoporosis, immune dysfunction, vestibular disorders, wound healing impairment, anemia, and aging (see Clément 2005 for review). The judicious use and application of experimental animal models to the study of complex biomedical and pathophysiological problems will continue to provide new insights into biological mechanisms that influence our lives on Earth and in space (Borlcowski et al. 1996).

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