A full menu for stem-cell research

The stem-cell meeting held at the Institut Pasteur in December 2004 proved that the nascent field of stem-cell biology has rapidly become one of the most exciting and active fields in current research. Leading scientists from a range of disciplines relevant to stem-cell biology covered a gamut of current topics, including the properties of human and mouse embryonic and adult stem cells, attempts to manipulate stem cells, and the first clinical attempts at cell-based therapies. Here we describe some of the high points.Stem cells are endowed with the ability to perpetuate themselves through self-renewal and to differentiate into many specialized cell types. This remarkable dual capacity raises many questions and holds enormous potential for regenerative medicine. A crucial question is how a stem cell decides to self-renew rather than to differentiate, and which signaling pathways are at work in the two different states. Recently, thanks to the work of several groups, including those of Peter Andrews (University of Sheffield, UK), Austin Smith (University of Edinburgh, UK) and our own, the molecular signature underlying the 'stemness' state of human embryonic stem cells (hES cells) is being defined. Andrews reported karyotypic changes in three independent hES cell lines involving the gain of chromosome 17q and occasionally 12p. These changes may provide a selective advantage for the propagation of undifferentiated hES cells, and a detailed analysis of the genes present in these chromosomal regions might further elucidate the molecular mechanisms underlying self-renewal. However, such detrimental karyotypic changes need to be taken into account for future therapeutic applications of hES cells. One of us (A.H.B.) reported work in our group on the importance of the Wnt and TGFβ pathways in maintaining stemness.The fundamental challenge of work on stem cells lies in unlocking the mechanism that directs the differentiation of pluripotent stem cells into specific cell lineag