Embryonic stem cells with identical genomes grow into distinctive tissues, such as heart, bone, and brain. At one time, scientists believed the differences among cell types arose from various sets of genes switched on inside developing cells. Then, studies showed that adult neurons uniquely lack a protein that permanently turns off neuronal genes in the rest of the body’s cells. Now, it turns out that precursor nerve cells contain that same repressive protein after all. In fact, the protein directs the complex network of genes that transforms an embryonic stem cell into a mature nerve cell, say Howard Hughes Medical Institute (HHMI) researchers. This new study, published in the May 20, 2005, issue of the journal Cell, may be among the first to track a set of genes from stem cell to differentiated neuron. It also reveals fundamental details of how stem cells retain developmental plasticity.
