The Effects Hypergravity on the Morphology of Xenopus Embryos

Early amphibian development is sensitive to both reduced and elevated gravitational force. But later, following gastrulation and neurulation, a critical population of cells must migrate from the dorsal neural tube outward to destinations throughout the body where they differentiate into a wide variety of critical tissues including head cartilage. These cells, the neural crest cells, respond to extracellular cues and signals that guide migration and differentiation in an intricate process that may also be sensitive to altered gravity. We examined the effects of hypergravity on the migration of neural crest cells to form head skeleton cartilage, and on body size in Xenopus embryos. To investigate this we centrifuged embryos at 7G or 10G, from yolk plug stage (gastrulation) through five days of development to stage 45 when feeding begins. A control group was placed on the centrifuge. After centrifugation, the embryos were fixed, cleared and stained with Alcian Blue to reveal cartilage. We then captured images for analysis to obtain body and head cartilage measurements. We found that hypergravity retarded the growth of Xenopus embryos, possibly via increased load on the cardiovascular system. Surprisingly, it also resulted in significantly larger and more asymmetrical head cartilages, when corrected for body size, but it did not result in a significantly higher frequency of malformations. Our results support the likelihood that hypergravity inhibits body growth and perturbs the formation of neural crest derived head cartilage.