Toads, fish, and nematodes: the space station’s odd menagerie
They are known as “model organisms”: flies, mice, zebrafish, frogs, and nematodes—all animals used by researchers in experiments, particularly because their biological structures are simpler than those of humans.
Simon Galas, University of Montpellier
This is crucial for basic biology and human health research, and it can be done both on Earth and in space. A prime example is NASA’s recent “Worm in Space” mission, launched in December 2018, which sent 360,000 Caenorhabditis elegans roundworms into space!
Animal experimentation in space is nothing new. A review of missions conducted by NASA from 1965 to 2011 reveals no fewer than 382 experiments carried out on various platforms: the Gemini capsule, biological research satellites, NASA shuttles, the NASA/MIR platform, and more recently, aboard the International Space Station (ISS), which has been in low Earth orbit since the 2000s.
The goal is to better understand the effects of the space environment on living systems, and on humans in particular. Astronauts, in fact, undergo gradual physiological changes that become more pronounced as their stay progresses. These changes can lead to an increased risk of various conditions, including fractures, vision loss, increased intracranial pressure, anemia, muscle atrophy, acute radiation syndrome, and immune system dysfunction. Using model organisms subjected to the same stresses as astronauts helps prevent these problems from arising.
NASA
Model organisms were also used very early on in space missions to identify the fundamental behaviors of living organisms. For example: How does Earth’s gravitational force influence living organisms and their development starting from fertilization? Answering this question required numerous model organisms (plants, insects, fish, amphibians, small mammals) and no fewer than fifty experiments conducted in space.
A fertile toad
As early as 1965, frog eggs and fruit fly larvae (Drosophila melanogaster) carried aboard the Gemini mission showed normal development in the absence of gravity. Embryonic development was also tested in space during a famous 1992 experiment (the frog embryology experiment, Space Shuttle Spacelab Japan mission STS-47) conducted with a toad known as Xenopus (Xenopus laevis), which demonstrated that Earth’s gravity was not required for ovulation, fertilization, embryonic development, or the formation of tadpoles capable of swimming.
NASA
Experiments on other models have shown that the most critical processes of reproduction and development are independent of the level of gravitational force. One such experiment, conducted in 1979 during the Russian Cosmos 1129 mission, demonstrated the ability of pregnant rats to carry out normal pregnancies. However, subsequent experiments on very young rats revealed sensorimotor deficits and demonstrated reduced growth of motor neurons, thus indicating the existence of a period of sensitivity to gravitational force in the sensorimotor system during post-embryonic development.
Significant research has also been conducted in the fields of microbiology and infectious diseases. Given the growing recognition of the importance of our microbiome—which weighs about 2 kg—it’s easy to become concerned about potential changes that might occur to our microbial communities in space!
Virulence in Space
In 2006 and 2007, bacteria such as Salmonella enterica serovar Typhimurium (the causative agent of salmonellosis), Pseudomonas aeruginosa (nosocomial infections), Candida albicans (the fungus responsible for candidiasis), and Streptococcus pneumoniae (responsible for pneumonia) were sent into space, revealing the emergence of virulence traits that control cultures on Earth had not developed. Analysis of these bacteria revealed that they owed the emergence of their virulence in space to a single gene (Hfq), thereby demonstrating the immediate relevance of this discovery not only for preparing astronauts for their journeys but also for gaining a better understanding of these infectious bacterial agents, which are becoming increasingly resistant to treatment and responsible for numerous deaths each year on Earth.
Wikipedia
Another important topic: astronauts’ muscles change rapidly in space due to microgravity. Experiments to assess muscle changes in rats in space were conducted as early as 1965 by NASA. These experiments demonstrated a rapid decrease in muscle contraction strength, an increase in muscle contraction speed (velocity), a decrease in endurance with increased muscle fatigue, and a shortening of muscle fiber length. This last phenomenon has been linked in both rats and humans to the fetal posture adopted in space, which leads to gradual muscle atrophy.
The changes in muscle physiology observed in rats during spaceflight have been confirmed in humans and have led to the development of a set of exercises (walking and jogging on a treadmill) that astronauts are required to perform daily for 2.5 hours in order to slow down these changes, which can affect the muscles very rapidly at the beginning of a space mission.
The list below provides examples of observations made on model organisms during space missions in relation to human health:
- Chickens, geckos, quails, mice, and rats for studies on bone physiology in space;
- Fruit flies (Drosophila), human cell cultures, mice, and rats for observations on the immune system’s response to microgravity;
- Bacteria, fungi, cultured human cells, and yeast for studies on microbial growth and virulence;
- Chickens, mice, nematodes, and rats for studies on muscle physiology in space.
- Crickets, fish, quails, mice, newts, rats, toads, and snails for neurophysiological studies.
“Worm in Space”
NASA
The "Worm in Space" mission this December 2018 focuses on the nematode Caenorhabditis elegans. This non-parasitic roundworm, measuring one millimeter in length, can be found on most continents and feeds on bacteria in fungi, plants, or decaying fruit.
No fewer than three major discoveries in modern biology have already been made thanks to its meticulous observation, notably the mechanisms of apoptosis (programmed cell death) and the development of cancers resulting from abnormalities in this process. Nematodes are an ideal model for studying how the apoptosis process functions in space in order to prevent the risk of cancerous conditions among astronomers. They are associated, on the one hand, with exposure to dangerous radiation in space and, on the other hand, with possible alterations in the normal functioning of apoptosis, which is responsible for eliminating cells damaged by radiation.
This little worm is no stranger to space travel. During the STS-42 mission, conducted in 1992 aboard the Discovery shuttle, the nematodes managed to mate and reproduce over two generations without any apparent problems. But a few years later, the STS-76 mission, conducted in 1996 aboard the Atlantis shuttle, revealed something entirely different! An abnormal mutation rate was observed in the nematodes, indicating for the first time a direct effect of cosmic rays on living organisms.
Worms Survive the Columbia Disaster
Following these experiments, it was proposed that nematodes be used in space as dosimeters to inform astronauts about the risks of mutations caused by cosmic rays. The nematodes were also on board the space shuttle Columbia on February1, 2003, for the STS-107 mission. A tragic accident during the mission caused an explosion that shattered the spacecraft and killed all seven crew members. However, scientists managed to recover, from debris from Columbia that fell in Texas, a 4-kg container holding the nematodes from the scientific expedition. They had survived. Protected inside their container, they had already reproduced over several generations.
Let’s return to the “Worm in Space” mission. On Monday, December 3, the Soyuz MS-11 capsule docked with the International Space Station, carrying three astronauts and nearly 360,000 Caenorhabditis elegans nematodes. This experiment is designed to study the 40% loss of muscle mass that astronauts experience during long-duration missions. This loss is comparable to the muscle loss observed in men aged 40 to 80 as part of a natural process known as sarcopenia.
The muscles of the nematode
Placed in special bags with their artificial food, the nematodes will remain there for six and a half days, after which they will be frozen and returned to Earth for analysis in 2019. Several experiments will be conducted. One of them involves studying a control group of normal nematodes against another group of nematodes in which genes important for the normal functioning of insulin have been modified. This hormone is known to be linked to the mechanisms of senescence and aging through its effect on glucose utilization by tissues, particularly muscles. The use of genetically modified Caenorhabditis elegans with variations in glucose utilization will help better define insulin’s role in the process of sarcopenia. This study aims to better understand why human muscles weaken as people age in relation to the role of insulin.
Another experiment will aim to determine whether the expression of certain genes in C. elegans is altered by exposure to microgravity. During previous missions, it was observed that the expression of 150 genes in the nematode was reduced during a stay in space. This set of 150 identified genes will be studied again during this mission to determine whether certain drugs can prevent or slow muscle loss during spaceflight. A complementary experiment will examine the function of the nematode’s motor neurons, which trigger muscle contraction.
Other possibilities are emerging. For example, researchers are exploring the development of automated systems capable of sending nematodes to other planets to study their evolution over multiple generations. The general idea behind these space experiments is to gain a better understanding of how humans live in space in order to prepare for missions to Mars. And, here on Earth, to gain a better understanding of how the human body functions by observing the biological processes at work in the hostile environment of space.
Simon Galas, Professor of Genetics and Molecular Biology of Aging, CNRS – School of Pharmacy, University of Montpellier
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