Hippo and the Hydra – University of Innsbruck
A new study of the origin of the body axis in the immortal freshwater polyp Hydra. The so-called Hippo signaling pathway is responsible for this, which among other things ensures that our organs do not continue to grow indefinitely. The Institute of Zoology at the University of Innsbruck was significantly involved in the research and provides important data.
The body structure of most animals is based on an axis that runs from the head to the trunk. A major question in developmental biology is how the cells of the first multicellular animals organized themselves and how this body axis came about. A new study published in the journal Proceedings of the National Academy of Sciences (PNAS) shows that the evolutionary origins of the body axis lie in what is known as the hippo signaling pathway.
A signaling pathway forms the organs
Signaling pathways are molecular biological processes that serve to communicate between cells. Through the formation and exchange of certain molecules, cells can receive, process and respond to information from the environment or the body.
The Hippo signaling pathway has an important function in higher animals such as mammals and birds. It controls cell division in the developing organs and ensures that these assume their correct size and three-dimensional shape. If the hippo signaling pathway is defective, tissue thickening can occur, similar to the skin of a hippopotamus – hence the name.
Examined with electron microscopy
Researchers from the Lunenfeld-Tanenbaum Research Institute in Toronto and the Washington University School of Medicine, with support from the Institute of Zoology at the University of Innsbruck, have described the function of this signaling pathway in evolutionarily ancient animals for the first time. This is probably how the Hippo signaling pathway originally came about. To do this, the researchers examined the freshwater polyp Hydra.
The working group led by Bert Hobmayer at the Institute of Zoology has been working intensively on this model organism for years. Using electron microscopy, they examined the complex mechanism and provided important data on the internal organization of the cells, which are controlled by the Hippo signaling pathway.
“Hippo is a complex mechanism that is not yet fully understood in developmental biology,” says Hobmayer. “We have now found similar principles of action in the simply built hydra, which, however, apply to the complete animals.”
The immortal polyp
The hydra is a simply built beast gilded as being virtually immortal. It is constantly reworking its tissue, can completely replace entire body parts, or form an entire organism from individual cells. It also reproduces asexually by budding out of its body, then dying into a new clone. With each new bud, a new body axis is created.
The research results show that the Hippo signaling pathway influences the rate of cell division throughout the Hydra. He also controls the emergence of new animals. In addition to controlling tissue growth and asexual reproduction, the Hippo signaling pathway also produces signaling molecules that are necessary for the growth of a normally shaped body axis.
The researchers have not only come a big step closer to the development of a specific signaling pathway. With the new knowledge about the simply built Hydra, further studies with this model organism open up.
Financing: The study received support from the Barnes-Jewish/Christian investigator program, the European Commission’s Horizon 2020 funding program, and the National Institute of General Medical Sciences.
The research focus CMBI