19-P023 Anterior regeneration in the planarian Schmidtea mediterranea: Revisiting the works of T.H. Morgan and C.M. Child

Planaria possess a population of pluripotent adult stem cells called neoblasts, capable of differentiating into all cell types required to regenerate entire animals from almost any fragment. The regeneration of different fragments is catalogued in a body of classical experiments by many eminent scientists. Here, we endeavour to explore these classical observations and insights and combine them with molecular approaches in the planarian Schmidtea mediterranea. Morgan demonstrated that the early anterior blastema displays the potential to produce more than one head if divided laterally, while later in regeneration this plasticity is lost. Using the same non-molecular criteria as Morgan, we find that in S. mediterranea the anterior blastema is committed to form only one head immediately after anterior regeneration is initiated. However, the time taken to regulate regeneration and begin producing missing lateral structures increases with the length of time anterior regeneration has proceeded before the division. We have developed the spatiotemporal characterisation of this process as an assay to discover subtle RNAi regeneration phenotypes that are affected by this process, but ultimately result in otherwise normal regeneration. Child observed a delay in regeneration in anterior blastemas induced in more posterior positions. We have used a series of molecular markers to deduce that this difference may be observed as early as 24 h of regeneration. We investigate the possibility that there is a delay in specifying the fate of anterior blastemas produced from more posterior regions and explore the role of the hypothesised pre-existing Wnt signalling gradient in this phenomenon.