The embryonic brain of a frog is busy long before it is completely formed. What it usually does is supervising the process of forming the layout of complex patterns of muscles and nerve fibers by sending signals to the part far from it just a day after fertilization. So, if the brain of a frog embryo is missing, the growth of its body goes wrong, reported in Nature Communications on September 25.
The result of this research from brainless embryos and tadpoles helps the biologists to understand the signals of the brain which are involved in the correct development of muscles and nerve fibers. Scientists have usually researched short-range signals that occur between two neighboring cells, not a long one. So, this research is the first example of investigating long-range signals.
Celia Herrera-Rincon of Tufts University in Medford, Mass., and colleagues devised a simple way to observe the body growth of the brainless tadpole. They got rid of growing brains of the African clawed frog embryos just a day after fertilization. Surprisingly, they succeeded in becoming tadpoles from embryos without the brain and became innovative experiment result showing that some organisms can grow without a brain.
This experiment revealed that brains are not essential to the body growth of embryos. However, there are also side effects of having no brain. The brain directs and guides the behavior of the parts of the body before they fully grow. Normally, muscle fibers form a stacked chevron pattern. But in brainless tadpoles, they form incorrectly bungled pattern. “The borders between segments are all wonky,” says the study coauthor Michael Levin, also of Tufts University. “They can’t keep a straight line.”
Nerve fibers spreading on the body of the tadpole were also abnormally grown in the brainless frog embryos. Nerve fibers surrounding the bodies of the tadpoles formed a confusing pattern in the wrong places during their growth. Muscle and nerve abnormalities have been found to be the biggest problems, and major organs such as the heart are also thought to be defective in those embryos, and further research is required to clarify those defects.
In addition, the growth process of brainless embryos was interrupted by certain substances that would not interfere normal embryo’s development. Therefore, it might be reasonable to conclude that the brain of a frog embryo blocks harmful substances at the beginning of its growth.
Scientists were also interested in how the brain transmits long-distance signals to distant cells during the growth process. They do not know the exact process but have some idea about it. Injection of chemical messengers and proteins like acetylcholine and HCN2 improved the development of muscle system in brainless frog embryos. However, further research is needed to find out if those injections are actually mimicking the process of the embryo’s brain.
Although frogs and mammals cannot be identified as same, it seems plausible that this principle can be applied to humans because the substances forming the bodies are fundamentally same in both organisms.