Model organisms on Earth and in space
Guest post by John Hatch
John will be available to discuss this post and answer your questions about Genes in Space at the next #GenesInSpaceChat on Tuesday, March 13th at 8pm EST. Submit your questions for John HERE.
One question we are commonly asked is 'can my Genes in Space experiment be conducted on astronauts?' For the proposal stage of the contest we want you to think big and propose the best DNA experiment you can think of to answer your question so you are allowed to use astronauts in your proposal. However, it may be worth considering whether or not humans are really the best system for your experiment. At most there are seven astronauts aboard the International Space Station at one time, perhaps not enough subjects to get conclusive results. Additionally there are many ethical considerations that may limit your experimental options. Model organisms can be a great alternative to human research and may be worth considering for your DNA experiment in space.
Wheeler & Brändli 2009 Dev Dyn 238:1287-1308.
What is a model organism?
Model organisms are non-human species researchers use to learn about biology. They come in many shapes and sizes, from single-celled bacteria to primates like monkeys. Since all life on earth has a shared evolutionary history, all of these species have important biological similarities to humans, and what we learn from them can be applied to better understand human health and disease. As you’ll see in this post, different organisms are chosen for different research purposes, but all model organisms have some traits in common. Most importantly, these species are generally easy to keep and breed in a laboratory setting, often in large numbers. We also already have a lot of knowledge about most model organisms, including their genetic makeup, which helps place new discoveries in context. When selecting a model organism to study a question that interests you, it’s important to understand both the advantages as well as the limitations of the (many!) species used in research.
Single-celled model organisms
Simple, single-celled organisms are the best
models for studying the most basic molecular functions of cells. They can
reproduce rapidly by the billions, enabling researchers to test hundreds or
thousands of options in one set of experiments.
Bacteria, especially Esherichia coli, help us learn how cells copy their DNA, correct errors, and make new proteins.
Saccharomyces cerevisiae (beer yeast), is eukaryotic, like humans, meaning the structure of yeast cells and their genomes are much more similar to ours than bacteria. This similarity has taught us how cells divide and how certain genes can be expressed at specific times. Cancer drugs that interfere with cell division are based on discoveries from single-celled model organisms.
Invertebrate animal modelsAs useful as single-celled organisms are, understanding how cells work together in a complex multicellular organism requires plant and animal model organisms. Roundworms (Caenorhabditis elegans) and fruit flies (Drosophila melanogaster) are two of the most extensively studied non-vertebrate animals. Each of these organisms is easy to breed in large numbers in laboratories, and both are used extensively to understand animal genetics as well as intercellular communication systems, especially with regard to development and behavior. Many of the key genes involved in the growth of an organism from a fertilized egg to a mature individual were first revealed in these animals.
C. elegans is simple enough that scientists can track the development and
fate of every single cell in the entire animal, allowing researchers to test
the function of individual genes or mutations with incredible detail. They are also transparent allowing individual cells to be tracked during development.
Drosophila has only four pairs of chromosomes, which enabled sophisticated genetic approaches before the advent of modern genetic techniques.
Vertebrate animal models
When a new discovery is made in yeast or flies or worms, it might not be immediately apparent whether that insight is relevant to human biology. For this reason, many animal models are vertebrates (animals with a spinal cord), a category that includes humans.
Xenopus laevis, a species of frog, is a popular organism for studying development, because their eggs and early embryos are quite large, making observations of their development much easier than in other species.
Zebrafish (Danio rerio), breed happily in captivity, and their young are transparent during development, meaning that scientists can watch organs grow and change in living animals. Recent advances in zebrafish genetics have also allowed scientists to manipulate zebrafish in exciting new ways, and investigate processes like cancer or heart disease.
Mammalian model organisms
Although our vertebrate cousins have provided huge amounts of useful data, to really understand human biology it is often necessary to look even closer to us on the tree of life. For this reason, many labs employ mammalian model organisms, especially rodents like mice (Mus musculus) and rats (Rattus norvegicus). Because these animals are our close cousins, they share most important aspects of physiology with humans: they have similar circulatory, respiratory, and reproductive systems, and mammals are the only animals with a cortex in the brain (the advanced structure that humans use for most of their thinking). For these reasons, most drug development involves an early stage of testing in rodents, and many studies of mammalian health, cognition, or reproduction use these species, since these processes are not accurately modeled by flies or fish.
By now, it should be clear that our modern understanding of biology depends on insights from many different forms of life — and there are many more model organisms than are listed here! Very little of our knowledge has come from a single organism or species. By studying species across the whole tree of life, scientists are able to learn exciting new things, from the basic molecular processes of individual cells, to the collective functions of the brain that allow us to move, think, and discover even more biology.
Due to their importance here on Earth, most common model organisms have been brought to space and helped contribute to our understanding of how life is affected by cosmic conditions. You can learn more about this research on NASA's Space Biosciences page or browse research by species on NASA GeneLab. As you develop your DNA experiment for space, consider using a model organism in your Genes in Space proposal.