Medaka Osteoclast (Medaka Osteoclast) - 07.05.17

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
Enhancement of the osteoclast (bone resorption cell) is assumed to cause the decrease of bone mineral density in space. Medaka fish is a model animal for the life science research, and JAXA plans to study the effects of microgravity on the osteoclast activity and the gravity sensing system of the vertebulate using Medaka fish on board the Kibo Module.
Science Results for Everyone
Chew on these results. Jaw bones of Japanese medaka fish in microgravity show decreased mineral density and increased volume of osteoclasts, cells that break down bone tissue. Some genetic changes in tissue from the brain, eye, liver, and intestine were seen in the space fish. However, the intestine appeared to be most sensitive to microgravity. No significant gene changes were detected in ovaries or testes. Microgravity slightly disrupted egg creation in these fish but there was no delay in body growth and maturation. These results improve understanding of the mechanisms behind bone density and organ tissue changes in space.

The following content was provided by Akira Kudo, and is maintained in a database by the ISS Program Science Office.
Information provided courtesy of the Japan Aerospace and Exploration Agency (JAXA).
Experiment Details

OpNom: Medaka Osteoclast

Principal Investigator(s)
Akira Kudo, Tokyo Institute of Technology, Japan

Yoshiro Takano, Tokyo Medical and Dental University, Tokyo, Japan
Keiji Inohaya, Tokyo Institute of Technology
Masahiro Chatani, Tokyo Institute of Technology, Yokohama, Japan
Akiko Mantoku, Tokyo Institute of Technology, Japan
Kazuhiro Takeyama, Tokyo Institute of Technology, Japan

Information Pending

Sponsoring Space Agency
Japan Aerospace Exploration Agency (JAXA)

Sponsoring Organization
Japan Aerospace Exploration Agency

Research Benefits
Information Pending

ISS Expedition Duration
September 2012 - September 2013

Expeditions Assigned

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • During the space flight, bone mineral density is decreased by the influence of osteoclast activation, which molecular mechanism is expectantly investigated. To find the effect of microgravity on osteoclast in space, we perform a long-term experiment with small fresh water fish, medaka, and examine the alteration of osteoclast activity under microgravity with the histological analysis or the gene expression analysis by RNA in-situ hybridization.

  • Medaka will be launched by SpaceX-2 and 2months experiment will be started using the Aquatic Habitat. After approx. 2weeks, 1month, and 2months from the experiment start, medaka will be sampled from the Aquatic Habitat Aquariums and chemically fixed for the retrieval. Also, the Aquatic Habitat maintenance operations, such as water sampling, water quality check, water exchange, and ORU exchanges are planned.

  • Fixed samples will be retrieved by SpaceX-2 and SpaceX-3.

Information Pending

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Space Applications
Information Pending

Earth Applications
Information Pending

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Operational Requirements and Protocols
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Decadal Survey Recommendations

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Results/More Information

Japanese medaka is a vertebrate fish species commonly used for scientific research because they are smaller than zebrafish in the genome size, can live in a much smaller area, and consume less food, water, and oxygen. This and the fact that the species have mated successfully in space make them ideal for raising from juvenile to adult in the Aquatic Habitat (AQH) system under the microgravity environment of the International Space Station (ISS). Scientists study the medaka’s cellular activities of bone formation and resorption in the gravity sensitive pharyngeal region, which contains hundreds of teeth in the adult fish and where many osteoclasts (cells that break down bone tissue) are found. Observation shows the fish becoming accustomed to life under microgravity by displaying unique behaviors such as upside-down, vertical, and tight-circle swimming. In addition, it is found that the mating behavior at day 33 under microgravity is not different from that on earth. Interestingly, they tend to become motionless at day 47, suggesting reduced muscle movement. Tooth development in terms of tooth germ formation is normal in the flight group. Live-imaging is useful to examine real-time alterations of cells under microgravity, and whole-body fish analysis revealed that exposure to microgravity immediately induced dynamic alteration of gene expression levels in osteoblasts and osteoclasts. During 56 days in microgravity, the mineral density of the upper pharyngeal bone and the tooth region decreases about 24%, along with an increase in osteoclast volume compared to ground control fish. Taken together, results indicate impaired physiological function and reduced mechanical use of the body under microgravity, as well as osteoclast activation as an effect of stress caused by weightlessness. One study also examines the ovary, intestine, testis, liver, brain, and eyes, and focuses on the biological impact microgravity has on these fish organs. The analysis of 5345 genes from the six tissues reveals similar but highly tissue-specific changes. Eleven genes are upregulated (the process by which a cell increases the quantity of a cellular component, such as RNA or protein, in response to an external stimulus-the opposite to downregulation) in more than four of the tissues examined, indicating common immune system and stress responses to spaceflight. A few genes in the brain and eyes show response to the space environment. By contrast, more than 2,500 genes change their expression levels in the caudal (near the tail) part of the intestine, suggesting that this organ is highly sensitive to microgravity stress. Many genes are downregulated in the liver but without accompanying tissue abnormalities. No significant alterations in gene expression levels (i.e., more than a twofold difference) are detected in the ovary. However, expression levels of genes for egg envelope proteins are suppressed in the ovary, and oogenesis (creation of eggs) is slightly disrupted in space fish, even though body growth and maturation are not delayed. For the testis, structures such as spermatocytes, spermatids, and spermatozoa are similar between the flight and ground groups, suggesting that normal spermatogenesis is maintained during spaceflight. These results shed light on the mechanism underlying the regulation of bone physiology and organ tissue changes under microgravity.

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Results Publications

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Ground Based Results Publications

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ISS Patents

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Related Publications

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Related Websites

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image Aquarium holding the Medaka Osteoclast ground testing (JAXA)
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