File:A Planarian neoblasts (green) are present throughout the mesenchyme of the animal and express category 1 genes..jpg

English: Neoblasts give rise to cells that express category 2 genes and to cells that express category 3 genes. It is not yet clear whether neoblasts can directly give rise to category 3-expressing cells, or whether those cells must first enter a temporary category 2-expressing state. Regardless, cells that express either category 2 or category 3 genes are more peripherally located than the neoblasts, indicating that as neoblasts differentiate, they turn on different gene expression programs and move toward the periphery of the animal. Many of the identified genes have been assigned particular functions based on RNAi experiments, while others await careful characterization. Not all genes are listed and descriptions of gene functions are discussed in the text. B RNAi of Smed-βcatenin-1 causes stem cell progeny to acquire a head fate regardless of the location of amputation. In contrast, RNAi of Smed-APC-1 causes stem cell progeny to adopt a tail fate. C Molecular markers of anterior and posterior fate on day 4 of regeneration following amputation down the center of the animal. After RNAi of Smed-βcatenin-1 (low β-catenin activity) or Smed-APC-1 (high β-catenin activity), stem cell progeny along the entire amputation plane adopt an anterior or posterior fate, respectively. Images provided by George T. Eisenhoffer. the authors, and adapted from (Gurley et al., 2008).