Microgravity and hypergravity effects on fertilization of the salamander Pleurodeles waltl (urodele amphibian)

Effects of microgravity (mu G) on fertilization were studied in the urodele amphibian Pleurodeles waltl on board the MIR space station. Genetic and cytomorphologic analyses ruled out parthenogenesis or gynogenesis and proved that fertilization did occur in mu G. Actual fertilization was demonstrated by the analysis of the distribution of peptidase-1 genes, a polymorphic sex-linked enzyme, in progenies obtained in mu G. Further evidence of fertilization was provided by the presence of spermatozoa in the perivitelline space and in the fertilization layer of the mu G eggs and by the presence of a female pronucleus and male pronuclei in the egg cytoplasm. Experiments in mu G and in 1.4G, 2G, and 3G hypergravity showed for the first time that, compared to eggs in 1G, several characteristics of the fertilization process including the cortical reaction and the microvillus transformations were altered depending on the gravitational force applied to the eggs. Microvillus elevation, the most evident feature, was reduced on mu G-eggs and amplified on eggs submitted to 2G and 3G. No lethal consequences of these alterations on the early development of mu G-eggs were observed.