Bioelectricity and tissue regeneration in planariaPlanaria are small freshwater flatworms. (Fig 1) When a planarian loses its tail or head, it grows a completely new one. It can even grow a new head and a new tail simultaneously if both are amputated. Even a fragment as small as 1/279th of the original worm can re-grow an entire, anatomically perfect, fully functioning animal within a week or so. This is accomplished by a population of stem cells (Fig 1B) that receive signals to tell them where they are in the body and which structures need replacing.

Fig 1).D japonica. Note the dark eye spots in the head and the pharynx (feeding tube) in the centre. Stem cells are labelled green. (Images from a 2009 project).

But what cues stimulate stem cells to regenerate into the appropriate tissues? Early experiments suggested that an external electric field controlled the polarity of planaria head/tail regeneration (Steele & Lange, 1977), but this observation remains poorly understood.

Aim: This project tests the hypothesis that an endogenous electrical field controls head/tail regeneration polarity in planaria.

Experimental plan: Planaria fragments will be exposed to electric fields of various intensities and durations to assess the effect on regeneration polarity. The electrical properties of the amputation stumps will be measured with a voltage-sensing electrode to determine whether the applied electric field affects the normal electrical pattern in a way predicted to affect regeneration. In some cases a charged, fluorescent dye will be injected to visualise its molecular gradient in the worms (with and without external electric fields).

Techniques: Microdissection, time lapse video microscopy, fluorescence microscopy, immunofluorescence, electrophysiology, quantitative image analysis, planaria colony maintenance, data handling with Excel spreadsheets and statistics software.

Relevance: Mammals are very poor at regeneration so research is increasingly exploring the potential for stem cell therapies. With the advent of RNA interference (RNAi) techniques planaria are emerging as a powerful research model for adult stem cell biology. This project will benefit from the expertise of a previous Honours project student, StephAnnand, who loved the worms so much she stayed to study them as her PhD project. Steph’s “proof of concept” experiments have shown that worm polarity can indeed be influenced by application of an electric field with a polarity opposite to the endogenous one (Fig 2).

Fig 2) Regenerated head where a tail should be. A worm fragment (missing its head and its tail) was placed in an electric field opposite to its natural electrical polarity for 24 h after amputation. (Image courtesy of S Annand).

Some References: Sanchez Alvarado, A. (2006). Planarian

regeneration: its end is its beginning. Cell 124: 241-245.

Steele, V and Lange, C.S. (1977). Characterisation of an organ-specific differentiator substance in the planarian Dugesiaetrusca. J. Embryol. Exp. Morph. 37:159-172.

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