Commentary. Death of early chick embryos during space flights

See slide presentation about this research (large images!). I you are connecting with a slow modem (less than 56pbs) this will take a long time. 

Dr. Cesar D. Fermin
Department of Pathology & Lab Medicine
1430 Tulane Ave/ SL 79
Tulane Medical School
New Orleans, La 70112-2699
(504) 584. 2618
(504) 587-7389 (FAX)
email: cfermin@tulane.edu
1. Problem: Three previous flights (STS-29, JEM, and SLM-1) flew fertile eggs (chicks and/or quails), and in every flight embryos of less than 24 hours of incubation died. On the other hand, fertile eggs that were pre-incubated at 1.0G for more than 36 hours prior to the launch survived at least 7 days of space flight.

2. Assumption: Embryos younger than 24 hours of incubation are irreversibly affected by microgravity, or unidentified variables other than microgravity.

3. Background: For over a century avian embryos served as and exceptional choice to evaluate the embryological development of the vertebrate inner ear. A good example of the chick usefulness as an embryological model is the popularity of books such as Development of the Chick by Frank R. Lillie. This book was copyrighted in 1908 and now in its third edition was revised in 1952 (Hamilton, 1952). Other great scientists used the chick for their developmental studies and their findings remain unchallenged today (Cajal, 1995a, Cajal, 1995b, Retzius, 1881). Rubel mentioned that embryological studies of the auditory placode were cited as early as 1831 (Rubel, 1978). A complete description of vertebrate development is found in many text books such as (Bodemer, 1968), and laboratory manuals such as (Lehman, 1977, Rugh, 1977). The following characteristics of the chick embryo offer advantages over the rodent models:

The majority of works published recently, utilizing quails as animal models, indicates that researchers follow the recommendations of Hamburger and Hamilton (Hamburger and Hamilton, 1951), which take advantage of the number of somites, appearance of eyes and beak and progression of limb development (Chevallier, 1979) for staging quails. Staging is necessary because similar aged embryos (days) may be of different stages. Chicks (Gallus domesticus) hatch between 18-21 days (stages 44-46), whereas quails hatch between 14-17 days. Thus, the staging schedule for quails is usually advanced by about 12 hours for days 3-6 of incubation (Halfter et al., 1985). Most work with quails deals with embryonic fate of cells in which a chimera of quail and chicken fertilized eggs are produced and cells from each donor is followed during development (Le, 1978, McCallion and Shinde, 1973, Yamada et al., 1991).

Japanese quails (Coturnix coturnix japonica) are, like chicken, ideal developmental models because of their short reproductive cycles of 16-21 days. The average life span of the quail is three years (Porter and Terril, 1986). Quails achieve adult coloration at about three weeks of age, they are easily startled with subsequent inducement of pecking behavior that can lead to cannibalism between animals. This behavior is however characteristic of most birds. Intermittent lighting following dark treatment is effective in stimulating egg production (O'Rourke, 1961). Thus, chicks from either species are suitable for flight experiments, and regardless of species being used, the why of embryos younger than 48 hours of incubation usually die in space should be further investigated by a including in future flights pre- and non incubated fertile eggs.

4. Variables to consider: It is well known that avian embryos are very hardy and can withstand prolonged periods of cold and heat. Avian embryos are also able to restart incubation (although at retarded stages) after changes in temperature, shock, etc. However, the degree of plasticity of avian embryos seems to be directly proportional to the embryological age (developmental stage) at 1.0G, where earth incubated embryos show significant variability in viability according to seasonal changes and incubating conditions (Florea, 1977).

The chick embryo is however not exonerated from the deleterious effects of radiation, electromagnetic fields, drugs, etc. The anesthetic Ketamine interferes with the development of endogenous rhythm of intrinsic activity, and with the development of reactivity of the generator of spontaneous motility in the chick embryo (Sedlácek, 1992). Other drugs of less selective use than ketamine, can also cause behavioral effects to early embryonic chicks in such way that chicks that survive to hatch, exhibit significant deficits in their pecking ability (Dose et al., 1995). Glucocorticoids for instance cause developmental retardation in Japanese quail embryos (Kaltner et al., 1993), and autonomic drugs can have a considerable effect upon blood pressure and heart rate (Tazawa et al., 1992). The effects of these drugs may be potentiated by the effect of physical variables present inside or around the incubator in the space enrironment.

There are in addition to the above findings, new data suggesting that, as yet fully unexplained, certain phenomena may act at the molecular level to alter developmental progression. For instance, protein transport in membrane (not across membranes) could be altered by hormones aided by water transport across the membranes (Haines, 1994). Conductive implants that shunt endogenous electric field away from the embryo caused defects (Hotary and Robinson, 1992). Changes such as those induced by electric and also ionic changes can affect gene expression leading to change in phenotype (Vandenbroeck et al., 1992). Ultraviolet light on the other hand can, similar to g-radiation, affect avian limb positional signaling, which in turn causes misdirection of the normal limb polarization (Honig, 1982).

Finally, weak extremely-low-frequency magnetic fields (PMF) have irreversible effect on the early development of less than 48 hours chick embryos (Ubeda et al., 1994). This work and other from the same laboratory indicate that viable fertile eggs exposed during the first 48 hours of postlaying to PMF (100Hz repetition rate, 1.0µT peak-to-peak amplitude, and 500 µs pulse duration) developed numerous abnormalities when surviving to older stages. Cultured cells expose to electromagnetic fields also responded by altering gene transcription (Phillips, 1993), suggesting that the effect of these environmental variables must be taken into account with experiments using avian embryos, even though growth variability in avian embryos probably contributes to a source for experimental error in improperly designed studies (Terol and Panchonruiz, 1994).

5. Conclusion: Chicks from either species are suitable for flight experiments, and regardless of species being used, the why of embryos younger than 48 hours of incubation usually die in space should be further investigated by a including in future flights pre- and non incubated fertile eggs. The above discusion of published information suggest that variables other than those previously examined and controlled for in previous flight experiments with avian embryos must be taken into consideration in the future. While there are probably other variables at play that were not studied before or that are unknown to me, examination of those above should prove a good start.

6. References cited: