Chop off the monster’s head and within the blink of an eye, it has regrown another. Of all the miracles of life that biology endeavors to explore, regeneration is at least among the top three.
With its voracious appetite for live prey, you could think of the three-banded panther worm, Hofstenia miamia, as a rice-sized monster. It is one of the greatest whole-body regenerators. Learning how this tiny worm can pull off such a feat could be key to discovering new ways of treating diseases and injuries.
New research models like H. miamia can reveal biological insights that are not possible through studies on more widely used model systems, but such investigations are limited by the tools and techniques that can be applied to probe the new organism’s biology.
To increase the depth of mechanistic approaches that can be used to study the three-banded panther worm, a new study led by Manasi Srivastava, PhD, associate professor of organismic and evolutionary biology and curator of invertebrate zoology in the Museum of Comparative Zoology at Harvard University, has resulted in the development of the ability to introduce foreign genes into the genome of this model organism that express consistently over generations, through a process called transgenesis.
“We developed a method for transgenesis in the acoel worm H. miamia, which has emerged as a new research organism for studying regeneration and stem cell biology,” the authors noted.
The findings are published in the journal Developmental Cell, in the article titled, “Transgenesis in the acoel worm Hofstenia miamia.” The study’s authors developed a toolkit that enables in-depth study of cellular and molecular mechanisms of development, whole-body regeneration, and stem cell biology in this new model organism that is capable of radical regeneration.
“[Transgenesis] is a tool that biologists use to study how cells or tissues work within the body of an animal,” Srivastava said. That this new model system is amenable to efficient random transgenesis opens doors for multiple downstream applications.
The authors devised a method for microinjecting fluorescent genes into embryonic cells to generate transgenic worms whose skin (epidermis), gut, and muscles glow red or green under ultraviolet light. Making a transgenic worm line takes about eight weeks in the Srivastava lab.
The authors showed that specific cell types can be isolated from this worm using these fluorescent markers, making studies on regeneration mechanisms possible through the tracking of photoconvertible molecules and live-cell imaging. The ability to make individual cells glow allowed the researchers to visualize the location, development, movement, division, and interaction of cells with each other, in the search for clues as to how they work together to orchestrate regeneration.
Precise genetic manipulation in the three-banded panther worm enabled researchers to switch off selected genes, disrupting the model organism’s built-in regenerative program. This can help researchers identify genes important for whole-body regeneration and their specific functions in the complex process. Using the transgenic worms, the researchers said they are most excited to study a population of pluripotent stem cells—cells that can produce all other cell types—that are critical in regeneration.
“We don’t know how any one of these cells actually behave in the animal during regeneration,” Srivastava said. “Having the transgenic worms will allow us to watch the cells in the context of the animal as it regenerates.”
The authors have developed a high-resolution three-dimensional view of cell morphology and demonstrated that the muscles of this work form a cellular scaffold for other tissues. Using the transgenic worms, the authors showed how muscle fibers in the worm connect to each other and to cells in the skin and the gut. Extensions from muscle cells interlock in tight columns and form a grid that offers the worm structure and support, much like a skeleton, the researchers observed.
In their future work, the team intends to probe further into the function of muscular networks in worms, delving into whether they store and relay information on regeneration in addition to forming a structural framework.
In 2010, as a postdoctoral fellow at the Whitehead Institute, Srivastava first became interested in these “absolutely charming” organisms when she collected these worms from a chilly Bermudan pond. Her earlier work has revealed DNA switches that control genes responsible for whole-body regeneration.
