A multinational team of scientists led by Tufts University biologists has succeeded in inducing a species of planarian, Girardia dorotocephala, to grow heads and brains characteristic of other species of planaria (Schmidtea mediterranea, Dugesia japonica, and Polycelis felina) without altering genomic sequence.

“It is commonly thought that the sequence and structure of chromatin – material that makes up chromosomes – determine the shape of an organism,” said Dr Michael Levin of Tufts University, who is the senior author of a paper published today in the International Journal of Molecular Sciences. “But these results show that the function of physiological networks can override the species-specific default anatomy.”

The finding that head shape is not hard-wired by the genome but can be overridden by manipulating electrical synapses in the body suggests that differences in species could be determined in part by the activity of bioelectrical networks.

The discovery could help improve understanding of birth defects and regeneration by revealing a novel pathway for controlling complex pattern formation.

“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,” Dr Levin said.

Working with the planarian Girardia dorotocephala, which has remarkable regenerative capacity, Dr Levin and his colleagues were able to induce the development of different species-specific head shapes by interrupting gap junctions, which are protein channels that enable cells to communicate with each other by passing electrical signals back and forth.

The changes were more than skin deep; they included not only the overall shape of the head but also the shape of the brain and the distribution of the worm’s adult stem cells.

The ease with which a particular shape could be coaxed from Girardia dorotocephala was proportional to the proximity of the target worm on the evolutionary timeline. The closer the two species were related, the easier it was to effect the change.

“Interestingly, the shape change is not permanent; after regeneration is complete, intact animals remodel back to Girardia dorotocephala-appropriate head shape within several weeks in a secondary phase of remodeling following initial complete regeneration,” the researchers said.

“We’ve demonstrated that the electrical connections between cells provide important information for species-specific patterning of the head during regeneration in planarian flatworms,” said lead author Maya Emmons-Bell, also of Tufts University.

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Maya Emmons-Bell et al. 2015. Gap Junctional Blockade Stochastically Induces Different Species-Specific Head Anatomies in Genetically Wild-Type Girardia dorotocephala Flatworms. Int. J. Mol. Sci. 16 (11), 27865-27896; doi: 10.3390/ijms161126065