During development, cells must differentiate into specific types. This process was understood for many years to be an irreversible event, yet recent papers have challenged this idea. In one paper, researchers have been able to convert fibroblasts into neurons by expressing a specific set of genes. Image above shows these induced neuronal cells, only a few days after they started out as fibroblasts.
Reference: Thomas Vierbuchen, Austin Ostermeier, Zhiping P. Pang, Yuko Kokubu, Thomas C. Südhof, and Marius Wernig. Adapted by permission from Macmillan Publishers Ltd: Nature 463, 1035-1041, copyright 2010. Paper can be found here.