Figure 1. The model of hierarchical organization of pancreatic cancer cell population. The pancreatic cancer stem cells and their progenies in differentiation can develop to single colonies with different morphologies. Based on the in vivo and in vitro characteristics, holoclones correspond to the cancer stem/ progenitor cells, while paraclones correspond to the fully differentiated cells and meroclones correspond to the cells in the intermediate stage. The genes and microRNAs that associate with cancer stem cells and support chemoresistance, including BMI1, GLI1/2, CXCR4, mir-21/214/221/222/155, are enriched in holoclones. However, the Let-7 and mir-30a/b/c are enriched in paraclones. (Adapted from Tan et al., 2011 [26]. Open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited).