Effects of space flight on Xenopus laevis larval development

Abstract

Fifty-three fertilized Xenopus laevis embryos at early tail bud stage were launched into orbit aboard a Biocosmos satellite and remained in microgravity for 11.5 days. During this period, the embryos hatched and continued to develop as free-living larvae. Forty-eight individuals survived the mission. Upon recovery these tadpoles had smaller heads/bodies and proportionately longer tails than ground controls. Almost all the flight animals had caudal lordosis and consequently swam in backward somersaults. Compared to ground-based controls, their notochords were significantly larger in cross-sectional area and were deformed. Caudal muscle fibers were less dense and involuted in a fashion indicative of degeneration. In contrast, cranial muscles associated with buccal pumping did not differ between the flight and control animals. Upon landing, the flight larvae were found to be negatively buoyant and lay on the bottom when they were not swimming. They had significantly smaller lungs than controls, suggesting that they had failed to inflate their lungs in microgravity. Additionally, the branchial baskets, gill filters and thymuses all showed signs of retarded development or degeneration. The caudal deformity that we observed in the flight X. laevis has been independently observed in three other space flight experiments where embryos were launched then hatched in space. In contrast, Xenopus larvae from another orbital experiment that were raised from fertilization through hatching in space did not exhibit any caudal abnormalities. These divergent results suggest that either features of the launch itself (i.e., high acceleration and vibration) or an abrupt decrease in gravity during the tail bud stage detrimentally affects musculoskeletal development in anurans.

Xenopus development from late gastrulation to feeding tadpole in simulated microgravity

“…Although NCC derived elements make up more of the head skeleton and are thus more readily observed than mesodermal elements, we found that the only mesodermal element measured, the notochord, did not vary significantly among groups. We did not observe many of the spaceflight microgravity effects noted by Snetkova et al (1995), such as significant differences in body or tail length, caudal lordosis, or changes in notochord size and shape. But we did observe similar effects on the branchial basket, notably a more spherical shape and possibly less development of the gill filters.…”

“…The tadpoles, launched at the early tailbud stage (approximately one day old), exhibited caudal lordosis (also noted in a study by Horn, 2006), disproportionately long tails and short bodies, a failure to inflate their lungs, and a reduced, misshapen branchial apparatus (Snetkova et al, 1995). The acceleration and vibration of the launch and the sudden onset of μG may have caused or contributed to these irregularities.…”

“…The notochord was chosen as a non-NCC derived skeletal element that had been described in previous microgravity studies in Xenopus (e.g. Snetkova et al, 1995). Specimens were also assessed individually for skeletal abnormalities.…”

Microgravity-induced modifications of the vestibuloocular reflex inXenopus laevistadpoles are related to development and the occurrence of tail lordosis

“…Behavioral modifications included swimming abnormalities Snetkova et al, 1995;Fejtek et al, 1998) and a depression of both gain and amplitude of the roll-induced static vestibuloocular reflex (rVOR) but not of the dynamic VOR induced by horizontal lateral displacements (Eßeling et al, 1994a;Eßeling et al, 1994b). Morphological modifications include a hyperextension of the tail (tail lordosis) (Fig.·1), and were observed in Xenopus laevis tadpoles launched before hatching (Snetkova et al, 1995;Sebastian and Horn, 1998) but not in tadpoles that developed from eggs fertilized in orbit under microgravity (Souza et al, 1995) (cf. Table·1).…”

“…Tail lordosis might be caused by weight deloading during g-exposure because affected tadpoles showed muscle degeneration (Snetkova et al, 1995). However, other factors such as: (1) trophic effects of vestibular activity on muscle development, and (2) the rostrocaudal maturation gradient, might cause tail lordosis if they revealed a sensitivity to altered gravity.…”