Irv Weissman was my professor at Stanford in the 1970's. He is a great man and good scientist but he is not always right. For example, throughout the late 1990's and up to 2007, he strongly denied the possibility of dedifferentiation and transdifferentiation, saying that cells don't go backwards after they have differentiated (unless they become cancer cells) and don't convert to become another type of cells. He represented the old guard (I was taught, for example, that differentiation is a one-way street when I was a graduate student) even when the data suggested strongly that some stem cells were switching from one type to another.
The discovery that embryonic stem cells can be cloned by transferring a nucleus from a somatic cell into an egg did not convince him that dedifferentiation was possible. The Yamanaka iPS story probably swayed him because he was not so vocal on the subject after 2007. It was not until Marius Wernig found that he could reprogram fibroblasts to become neurons in Weissman's own institute at Stanford around 2009 that Weissman relented on the issue of transdifferentiation. Transdifferentiation and dedifferentiation are now of course moot issues. While it may be difficult to get stem cells to change from one type to another by feeding them different nutrients and growth factors, the vast majority of scientists believe that it is a matter of changing the expression of several genes.
Several years ago, Weissman was the President of the International Society for Stem Cell Research. I remember attending a luncheon for sponsors and speakers in which Weissman gave a talk attacking mesenchymal stem cells. He pointed out that there are no reliable markers for mesenchymal stem cells and that a majority of studies making claims about mesenchymal stem cells having beneficial effects on animals really did not document what cells they transplanted. He was and is still pointing out that the scientific studies are not very good and that we must be more critical. He is right of course but this does not mean that mesenchymal stem cells do not exist and are not beneficial in certain conditions.
Science is not and should not be an authoritarian endeavor. Evidence matters. No scientist, no matter how important and great, is always right, particularly at the frontiers of knowledge where we don't have enough information and what I call the fog of discovery shrouds everything. Much of what we know depends on how good our tools are. At the present, most scientists rely on surface "markers" that cells express to classify them. These markers are often misleading. Nature is usually more complicated than we think. So, rather than by saying the Irv Weissman should be believed because he is a great scientist, we should be saying that scientists don't agree and that we don't know enough to come to a consensus.
Originally Posted by GRAMMY
Last edited by Wise Young; 04-18-2013 at 09:24 AM.
Last edited by PC720; 04-28-2014 at 04:04 PM.
It would be tough to live where research was restricted. I might have to move.