Effects of space environment on embryonic growth up to hatching of salamander eggs fertilized and developed during orbital flights.

In vertebrates, only few experiments have been performed in microgravity to study the embryonic development from fertilization. To date, these concern only amphibian and fish. We report here a study on the embryonic development of Pleurodeles waltl (urodele amphibian) eggs oviposited in microgravity. The experiment was performed twice on board the Mir space station and the data obtained included video recording and morphological, histological and immunocytological analyses. The data confirm that the microgravity conditions have effects during the embryonic period, particularly during cleavage and neurulation, inducing irregular segmentation and abnormal closure of the neural tube. Moreover, we observed several abnormalities hither to undescribed corresponding to cortical cytoplasm movements, a decrease of cell adhesion and a loss of cells. These abnormalities were temporary and subsequently reversible. The young larvae that hatched during the flight displayed normal morphology and swimming behavior after landing. The results obtained in the urodele Pleurodeles waltl are in accordance with those observed earlier in the anuran Xenopus laevis and in the fish Oryzias latipes.

Pleurodeles waltl, amphibian, Urodele, is a suitable biological model for embryological and physiological space experiments on a vertebrate.

Pleurodeles waltl (amphibian, Urodele) is an appropriate biological model for space experiments on a vertebrate. One reason for interest in this animal concerns the study of the effects of absence of gravity on embryonic development. First, after mating (on Earth) the females retain live, functional sperm in their cloacum for up to 5 months, allowing normal in vivo fertilisation after hormonal stimulation. Second, their development is slow, which allows analyses of all the key stages of ontogenesis from the oocyte to swimming tailbud embryos or larvae. We have performed detailed studies and analyses of the effects of weightlessness on amphibian Pleurodeles embryos, fertilised and allowed to develop until the swimming larvae stage. These experiments were performed in space during three missions on the MIR-station: FERTILE I, FERTILE II and NEUROGENESIS respectively in 1996, 1998 and 1999. We show that in microgravity abnormalities appeared at specific stages of development compared to 1g-centrifuge control embryos and 1g-ground control embryos. In this report we describe abnormalities occurring in the central nervous system. These modifications occur during the neurulation process (delay in the closure of the neural tube and failure of closure of this tube in the cephalic area) and at the early tailbud stage (microcephaly observed in 40% of the microgravity-embryos). However, if acephalic and microcephalic embryos are not taken into account, these abnormalities did not disturb further morphological, biochemical and functional development and the embryos were able to regulate and a majority of normal hatching and swimming larvae were obtained in weightlessness with a developmental time-course equivalent to that of 1g-centrifuge control embryos (on the MIR station) and 1g-ground control embryos.