Anterior Regeneration Of Dismembered Planaria Flatworm Tail

Model systems are important for both understanding and discovering new information about biological systems. Few organisms can regenerate limbs let alone entire bodies when injured, humans on one hand can regenerate few types of tissue when injured. However, a type of flatworm called planaria can regenerate its entire body even when cut in half or multiple pieces (Pagán, 2017).

This is due to planaria possessing neoblasts, a single type of pluripotent stem cell that can give rise to every cell type in the planaria’s body (Rink, 2013). It is for this reason that it is a critical model system for understanding the mechanisms behind regeneration through stem cells but also indispensable as a potential way to unlock the secret to allowing humans the ability to regenerate lost limbs.

We used three separate planaria worms dismembered laterally each at a separate point to determine the effect of location on regeneration ability. Planaria were placed into separate spring water-filled dishes and dismembered just below the head, across the pharynx (Figure 1), and just above the posterior end of the planaria. Each dismembered piece was placed into its own separate water filled dish. Each planaria worm piece was observed photographically over two weeks to determine regeneration ability in relation to cut site both anteriorly and posteriorly. Ice cubes were used to slow the movement of the worms for photography.

On Day 14 all planaria pieces were observed to determine regeneration ability. All planaria pieces successfully regenerated into fully developed and functioning worms regardless of the cut sight or observing anterior versus posterior regeneration ability. However, when observing the pharynx cut sight tail piece dish on Day 7 two separate planaria present while the other dishes contained only one respectively per planaria piece. Both planaria present in the dish were the same size and identical physically at Day 14.

In conclusion, based on prior literature it was hypothesized that the planaria would regenerate fully regardless of the cut sight, the results from Day 14 support this hypothesis. The discovery on Day 7 in the pharynx cut sight tail dish was unexpected and a definitive reason for the occurrence is unavailable. However, we hypothesize that the second planaria developed from tissue that became separated from the original tail piece at some point between Day 3 and Day 7. We have yet to determine if the spring water the planaria were stored in had a significant effect on the planaria’s ability to regenerate quickly.