Silkworm: The Underappreciated Life Science Model Organism
By Keping Chen, Ph.D.
The realm of insects is colorful and has been coexisting with human beings for countless generations. Insects appeared on earth more than 400 million years ago, and their descendants witnessed our evolution from upright, walking apes into complete human beings and observed the beautiful, magical, and endless waves of life on earth. There are millions of insect species on Earth, accounting for roughly half of all species on the planet. In the insect kingdom, Lepidoptera is a dominant order, with about 180,000 described species. And, as a representative of Lepidoptera insects, the silkworm (Bombyx mori), which originated in China, is a unique economic insect.
In recent years, with the rapid development of life science research, a number of model organisms have been established, such as fruit flies, mice, Escherichia coli, Arabidopsis, and other species, in order to explore the mysteries of life. Aside from producing silk, Bombyx mori also has been developed into a model organism in life science. In 2016, I authored a book, The model organism Bombyx mori, to bring attention to this particular field, and most recently my colleagues and I have shared this perspective in a detailed paper in the Journal of Insect Science.
Of course, many insects can be used as model organisms, but the silkworm as a model organism does have many unique advantages. The contribution of B. mori to genetics and immunology is almost identical with that of Drosophila. In recent years, with the completion of the silkworm genome and the discovery of many gene functions, B. mori has gradually become regarded as a model organism of life science, more than one of just Lepidoptera. In particular, this model organism has shown its advantages in investigation of microbial toxicity, environmental hazardous substances, and some genetic diseases.
Someone once commented to me, “Bombyx mori is too sensitive to toxic substances and is not suitable as a model organism.” Here is my answer: In a river of deep water, if you throw a stone into it, no ripples might be seen. But in a bowl of water, the water would splash with the throwing of the stone. So, I asked him, is it better to be sensitive or insensitive to know whether a stone was thrown into the water?
Another consider is scale. If there are 10,000 microorganisms to be tested for their toxicity using mouse models, you can imagine the time and cost, let alone safety and ethical issues. These matters become simple using the silkworm as the test organism. The silkworm is easy and efficient to raise, and its short lifecycle, large size, diverse mutant species, and other unique traits make it a very suitable model for genetics, cell development, disease, and drug-metabolism research. Although, we cannot deny that life science phenomena illustrated by B. mori still require further validation using advanced animals.
I have been engaged in silkworm research for more than 30 years, and it has always amazed me that this little creature eats mulberry leaves for 25 days and spits out 1,000 meters of silk. When can scientists completely crack the secret? How to achieve factory-like production of silk? Silk is an ancient biological material, but many of its new applications in the medical field are being discovered. Silk has great rigidity and flexibility, which can be made into potential tissue materials and developed into various human muscles induced by stem cells.
Another interesting note: The amount of eggs laid and silk produced by a silkworm is a balanced energy allocation after eating mulberry leaves. At the molecular level, who is in charge of the energy allocation? How do we identify this dual functional “key” that starts to turn on one function when it requires more eggs laid and turn on another when it requires more silk produced? This is like balancing the relationship between eggs and meat in animal husbandry.
B. mori has nearly a thousand mutant strains, and analyzing the functions of genes sets up a reference for understanding human genetic diseases. Additionally, the contest between B. mori and its viruses sets up an excellent model for developing baculovirus insecticides.
The Chinese character for the word “silkworm” is very intuitive, meaning the gift of life. Sericulture originated in China and benefited all mankind. The “Silk Road” was once known to the world, and now the “Belt and Road” will be again. Silkworm as a model organism has emerged for life science research, and I believe that through the efforts of scientists, the mysteries of this little creature will be gradually deciphered in the future.
Our paper in the Journal of Insect Science aims to provide new ideas and insights for life science research and agricultural pest control and utilization, as well as for the sake of human health. We hope that our views and perspectives can further broaden the field of silkworm study in life science research and lead and promote the scientific development of sericulture.
Journal of Insect Science
Keping Chen, Ph.D., is an entomologist at the Institute of Life Sciences at Jiangsu University in Zhenjiang, China. He is currently working on a book titled Dream Worm, a popular science reading on the silkworm, soon to be published. Email: firstname.lastname@example.org