The aim of our work is to understand how stem cells replace lost neurons after injury utilizing freshwater planarians (non-parasitic flatworms) as model organisms. Adult planarians maintain a population of pluripotent stem cells, which serve to replace cells lost after wounding or during normal physiological turnover. One of the truly remarkable properties of planarians is their ability for repair and regeneration of the central nervous system (CNS), a capacity that is limited in most animal models currently studied. Thus, planarians are excellent models in which to investigate fundamental mechanisms regulating stem cells. We are capitalizing on the molecular tools available to study planarian regeneration to identify and functionally characterize genes with critical roles in the CNS repair.
To advance our knowledge of how regeneration and patterning is achieved in the CNS, we are characterizing when and where neurons are born during regeneration. During the reporting period, we have successfully generated reagents that recognize planarian proteins. We are currently characterizing these markers and will use them, in combination with staining of proliferating cells, to analyze the transition of stem cells to specific neuronal cell types. To identify genes that are differentially expressed during regeneration of the CNS, we have carried out high-throughput gene expression studies (microarray analyses) using samples obtained from newly replaced tissues during early regeneration of the planarian head. Our experiments have revealed >1000 genes changing their level of expression in the regenerating tissues compared to control tissues obtained from uninjured animals. We have begun to examine the pattern of expression of these genes in the animal; the on-going expression screen has revealed more than one hundred genes expressed in the CNS, regenerating tissue or the stem cell population. Finally, based on their pattern of expression, we have targeted genes for studies aimed at characterizing their function during regeneration.
Successful identification of genes with no known or emerging roles in stem cell regulation would help to fill gaps in our knowledge of conserved biological mechanisms orchestrating proliferation and differentiation of stem cells in the CNS. This information has the potential to contribute to our ability to induce human embryonic or adult stem cells to divide and acquire neuronal fates, which would be valuable for therapeutic applications.