Flatworms are remarkable creatures, some of which have almost unbelievable abilities of tissue regeneration and growth. One particular species, Girardia dorotocephala, has been shown to be able to take this ability one bizarre step further: Researchers at Tufts University have successfully induced it to grow heads and certain brain structures of several other flatworm species on a temporary basis, all without altering its genetic sequence. Their findings are reported in the International Journal of Molecular Sciences.
The shape of an animal's body is largely determined by its genome. However, bioelectric networks of nerves and their connections (synapses) have their own way of forming constructs, and the careful manipulation of these can cause unique features to form in certain organisms, overriding the genetic material’s instructions.
With this in mind, the team of researchers decided to modify the synaptic connections in the head of their chosen flatworm to see if they could force it to produce new shapes. After decapitating them, the electrical connectivity between cells in its upper body were altered using a form of alcohol (octanol).
Incredibly, this caused the flatworms to grow not just new tissue, but entirely new heads – heads belonging to completely different species of flatworm: S. mediterranea, D. japonica, and P. felina. Not only were the head shapes replicated, but segments and characteristics of their brains were also seemingly copied, including the distribution of adult stem cells. The closer the two species were related, the easier it was for the researchers to induce the changes.
These changes, oddly, weren’t permanent: Within a few weeks, the genetic coding overcame the bioelectrically-induced head change, and their heads gradually returned to their original form. At present, the researchers aren’t entirely sure how this remodeling occurs.
Regardless, the fact that this all occurred without changing the DNA of the original flatworm is the study’s most significant discovery. This means that changes in a flatworm’s ability to “build” itself can sometimes originate from outside the instructions coded in its genetic material. This type of externally-induced alteration is known as epigenetics – literally meaning “extra growth.”
Transferring a selection of genes from two parents to their offspring isn’t the only way the building instructions for an organism are inherited. Along with an additional process called horizontal gene transfer employed by certain microscopic organisms, changes in the way genes are expressed can also be inherited. Several environmental or otherwise external factors can change the way cells read genes, meaning that the physical attributes of the offspring may be different – all without changing the DNA sequence.
Although it has yet to be shown whether or not these unusual flatworm changes can be transferred to their offspring, they do fit within the definition of epigenetics – although as some point out, without the inheritance being demonstrated, applying this definition can be somewhat controversial.
Nevertheless, the study has implications outside of just flatworm biology. Maya Emmons-Bell, a Tufts University biology undergraduate and first author on the paper, said in a statement: “This kind of information will be crucial for advances in regenerative medicine, as well as a better understanding of evolutionary biology.”
Image in text: G. dorotocephala (top left) was able to grow the heads of other species (top row) with no changes to its genome. Center for Regenerative and Developmental Biology, School of Arts and Sciences, Tufts University