flatworm grows different head
Tufts biologists induced one species of flatworm -- G. dorotocephala, top left -- to grow heads and brains characteristic of other species of flatworm, top row, without altering genomic sequence. Examples of the outcomes can be seen in the bottom row of the image.Center for Regenerative and Developmental Biology, School of Arts and Sciences, Tufts University.

Scientists in the US have made a flatworm grow a head and brain of a different species without altering its genomic sequence. The research has implications for the understanding of birth defects and regeneration, according to the team from Tufts University in Massachusetts.

The scientists published their findings in the International Journal of Molecular Sciences. In the study, they used a species of flatworm – Girardia dorotocephala – which has a remarkable capacity to regenerate. The induced the flatworms to develop head and brain characteristics of different species by interrupting protein channels that let cells communicate with one another by passing signals back and forth.

As well as changing the overall shape of the head, they also altered the shape of the brain and the distribution of adult stem cells. They did this with a number of different species and found the closer G. dorotocephala was related to the other, the easier it was to make the change.

Researchers say the findings show head shape is not necessarily determined by the genome, but can be changed by manipulating electrical synapsis, and this suggests different species could be determined in some part by bioelectrical networks.

Senior corresponding author Michael Levin said: "It is commonly thought that the sequence and structure of chromatin – material that makes up chromosomes – determine the shape of an organism, but these results show that the function of physiological networks can override the species-specific default anatomy. By modulating the connectivity of cells via electrical synapses, we were able to derive head morphology and brain patterning belonging to a completely different species from an animal with a normal genome."

The changed head and brain was only temporary. A few weeks after the flatworms grew different head shapes, they began remodelling again and re-acquired their original heads. How this happens will need further research, according to the team.

In terms of application, the researchers say the findings could improve the understanding of birth defects by revealing a new pathway for pattern formation – neural networks exploit bioelectric synapses to store and re-write information. Understanding how shape is determined could be used to fix birth defects or induce new biological structures to grow after injury. Maya Emmons-Bell, first author on the study, said: "This kind of information will be crucial for advances in regenerative medicine, as well as a better understanding of evolutionary biology."