RESUMO
Our ability to explore the cosmos by direct contact has been limited to a small number of lunar and interplanetary missions. However, the NASA Starlight program points a path forward to send small, relativistic spacecraft far outside our solar system via standoff directed-energy propulsion. These miniaturized spacecraft are capable of robotic exploration but can also transport seeds and organisms, marking a profound change in our ability to both characterize and expand the reach of known life. Here we explore the biological and technological challenges of interstellar space biology, focusing on radiation-tolerant microorganisms capable of cryptobiosis. Additionally, we discuss planetary protection concerns and other ethical considerations of sending life to the stars.
RESUMO
Tardigrades are highly tolerant to desiccation and ionizing radiation but the mechanisms of this tolerance are not well understood. In this paper, we report studies on dose responses of adults and eggs of the tardigrade Hypsibius dujardini exposed to gamma radiation. In adults the LD50/48h for survival was estimated at ~ 4200 Gy, and doses higher than 100 Gy reduced both fertility and hatchability of laid eggs drastically. We also evaluated the effect of radiation (doses 50 Gy, 200 Gy, 500 Gy) on eggs in the early and late embryonic stage of development, and observed a reduced hatchability in the early stage, while no effect was found in the late stage of development. Survival of juveniles from irradiated eggs was highly affected by a 500 Gy dose, both in the early and the late stage. Juveniles hatched from eggs irradiated at 50 Gy and 200 Gy developed into adults and produced offspring, but their fertility was reduced compared to the controls. Finally we measured the effect of low temperature during irradiation at 4000 Gy and 4500 Gy on survival in adult tardigrades, and observed a slight delay in the expressed mortality when tardigrades were irradiated on ice. Since H. dujardini is a freshwater tardigrade with lower tolerance to desiccation compared to limno-terrestrial tardigrades, the high radiation tolerance in adults, similar to limno-terrestrial tardigrades, is unexpected and seems to challenge the idea that desiccation and radiation tolerance rely on the same molecular mechanisms. We suggest that the higher radiation tolerance in adults and late stage embryos of H. dujardini (and in other studied tardigrades) compared to early stage embryos may partly be due to limited mitotic activity, since tardigrades have a low degree of somatic cell division (eutely), and dividing cells are known to be more sensitive to radiation.
Assuntos
Raios gama , Tolerância a Radiação , Tardígrados/efeitos da radiação , Animais , Proliferação de Células , Relação Dose-Resposta à Radiação , Fertilidade/efeitos da radiação , Reprodução/efeitos da radiação , TemperaturaRESUMO
Tardigrades represent one of the most desiccation and radiation tolerant animals on Earth, and several studies have documented their tolerance in the adult stage. Studies on tolerance during embryological stages are rare, but differential effects of desiccation and freezing on different developmental stages have been reported, as well as dose-dependent effect of gamma irradiation on tardigrade embryos. Here, we report a study evaluating the tolerance of eggs from the eutardigrade Milnesium cf. tardigradum to three doses of gamma radiation (50, 200 and 500 Gy) at the early, middle, and late stage of development. We found that embryos of the middle and late developmental stages were tolerant to all doses, while eggs in the early developmental stage were tolerant only to a dose of 50 Gy, and showed a declining survival with higher dose. We also observed a delay in development of irradiated eggs, suggesting that periods of DNA repair might have taken place after irradiation induced damage. The delay was independent of dose for eggs irradiated in the middle and late stage, possibly indicating a fixed developmental schedule for repair after induced damage. These results show that the tolerance to radiation in tardigrade eggs changes in the course of their development. The mechanisms behind this pattern are unknown, but may relate to changes in mitotic activities over the embryogenesis and/or to activation of response mechanisms to damaged DNA in the course of development.
Assuntos
Embrião não Mamífero/efeitos da radiação , Raios gama , Tardígrados/efeitos da radiação , Animais , Óvulo/efeitos da radiação , Tolerância a Radiação , Tardígrados/citologia , Tardígrados/embriologiaRESUMO
La siguiente revisión permite obtener una visión global de los diferentes estudios que se han llevado a cabo en la actualidad respecto a los tardígrados, principalmente a nivel molecular y genético. Los documentos consultados permiten un acercamiento a la anatomía del Tardígrado y al proceso de criptobiosis, así como a la taxonomía tradicional. Posteriormente, se abordan la genética y la biología molecular del Tardígrado, y se recopilan algunos de los resultados obtenidos respecto a su genoma, teniendo en cuenta genes o fragmentos secuenciados reportados en GenBank y estudios cromosómicos, con referencia a los métodos de extracción de ADN, taxonomía molecular, construcción de bibliotecas de ADNc y evolución-filogenia...
The following review allows a general vision of different studies that have been performed on Tardigrades, mainly those related to molecular biology and genetics. In general, this document shows some aspects on Tardigrade´s anatomy, cryptobiosis processes and the methodology of traditional taxonomy. Then we follow with some of the findings reported on the genetics and molecular biology of Tardigrades, taking into account sequenced genes or fragments reported in GenBank and chromosomal studies, likewise, with reference to DNA extraction methods, molecular taxonomy, cDNA library construction and phylogenyevolution...