Samantha Payne is a PhD candidate in the Shoichet lab at the University of Toronto and recent star of OIRM’s latest Stem Cells Inked video. We’re so excited that she agreed to write a post for us! Enjoy!
Imagine being able to repair your body back to a perfect state following an injury or even completely regrow an entire limb. Although this sounds like science fiction, there are a surprising number of groups in the animal kingdom, including fish, newts, and lizards, that can do exactly this. Some lizard species have the ability to voluntarily drop their tail in a process called autotomy (auto = self, tomy = cutting) and regenerate a functional replacement including all of the basic tissue types. Professor Matthew Vickaryous at the University of Guelph has dedicated his research to studying this extremely valuable phenomenon, and how it can one day be applied to humans.
Predation strategy turned regenerative phenomenon
The Vickaryous lab uses the leopard gecko as a model of tail regeneration. These small lizards are commonly found in pet stores and are bred commercially. In the wild, when a leopard gecko is threatened by a predator, it can initiate autotomy of the tail, which will quickly fall off of the animal and twitch wildly, distracting the predator and allowing the gecko to make a quick getaway. Amazingly, after only three days, the wound site has completely sealed over with a new layer of skin and a new tail has begun to grow underneath. The Vickaryous lab has shown that the new tail starts out as a mass of cells that is rapidly invaded with vasculature and nerves, and proliferates to elongate the tail. They have reported that the gecko is able to regenerate a fully grown replacement tail in about 1 month, making them a useful and easily-accessible tool to study regeneration.
The lab has extensively characterized the morphology of the new tail, and found that while some structures are close replicates of the original, others, such as the spinal cord, are not. Like humans, the original spinal cord of the gecko is organized into neuron bodies and projecting axons surrounded by the bony vertebrae. However when the tail regenerates, the vertebrae are not restored and are instead replaced by a cone-like structure composed of cartilage. Similarly to the vertebrae, this cone surrounds the regenerated spinal cord, although there are differences here too. The only part of the spinal cord that regenerates is the inner lining, called the central canal, which is made up of ependymal cells. These cells line the fluid-filled ventricles of the brain as well as the central canal of the spinal cord and are responsible for cerebrospinal fluid production. The ependymal cells also have another important role; in both mammals and non-mammals they are the source of a rare population of adult stem cells that are activated to initial regeneration following events such as traumatic injury.
Defining the mysterious ependymal cell
Current research in the Vickaryous lab led by PhD candidate Emily Gilbert is focused on characterizing the ependymal cells, and what their role in tail regeneration might be. She has observed using immunofluorescence imaging that these cells are actually not all one population of the same type but rather, they are divided into subsets that express molecular markers for different cells of the nervous system including neurons, astrocytes, and undifferentiated stem cells. This work suggests that the ependymal cells may have distinct functions and possibly even separate fates during regeneration, something that has not previously been documented. Unraveling the identity and function of these cells further will give us insight into the mechanism of spinal cord regeneration, perhaps one day even allowing us to determine what molecular signals are needed to replicate this regenerative process in humans to treat spinal cord injury.