The aim of our work is to understand how stem cells replace lost neurons after injury in a model organism of regeneration. Freshwater planarians (flatworms) are excellent models in which to investigate fundamental mechanisms regulating stem cells. These animals maintain a population of pluripotent stem cells in the adult, 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, we are capitalizing on the molecular tools available to study planarian regeneration to identify and functionally characterize genes with critical roles in the repair of the CNS.
To advance our knowledge of how regeneration and patterning is achieved in the CNS, we are analyzing when and where neurons are replaced during regeneration. During the reporting period we have begun to generate reagents that recognize planarian neural proteins. These protein markers will be used, in combination with staining of dividing cells, to analyze the transition of the stem cells to specific neuronal cell types. To develop protein markers we are isolating a cell fraction from the planarian head that is highly enriched with neurons, which will be used to immunize host animals to generate planarian-specific antibodies. Isolation of cell fractions is underway and we anticipate the generation of these reagents to be completed this year. To identify genes that are differentially expressed during regeneration of the CNS, we are performing high-throughput gene expression studies (microarray analyses) using samples obtained from tissue replaced in the early phases of regeneration of the planarian head after amputation. Initial experiments have revealed hundreds of genes that change their level of expression in the regenerating tissues compared to control tissues obtained from uninjured animals. We will examine the pattern of expression of genes with high levels of expression in the animal to determine which of these candidate genes are localized in the nervous system. Genes expressed in the CNS that share high similarity to human genes will be given high priority for studies aimed at characterizing their function during neural regeneration.