Do hematopoietic-to-nonhematopoietic conversions occur normally during embryonic development and in adult animals?
Almost all reported conversions between hematopoietic and nonhematopoietic cells in vivo were carried out by forced tissue relocations in irradiated or injured animals. For example, the experiments demonstrating a conversion from hematopoietic to epithelial cells were performed with irradiated animals. Irradiation, on the other hand, has been shown to destroy not only hematopoietic but also endothelial and epithelial tissues.131 It is therefore important to know whether such tissue conversions also occur under physiologic conditions. This question seems irrelevant if the ultimate purpose is to use somatic stem cells in tissue replacement therapies. However, knowledge about existing cellular processes might well be useful in guiding the development of tissue replacement protocols. In principle, tissue conversions might occur during embryonic development, involving the migration of hematopoietic cells from the yolk sac, aorta/gonad/mesonephros (AGM), or fetal liver to the anlagen of nonh
Almost all reported conversions between hematopoietic and nonhematopoietic cells in vivo were carried out by forced tissue relocations in irradiated or injured animals. For example, the experiments demonstrating a conversion from hematopoietic to epithelial cells were performed with irradiated animals. Irradiation, on the other hand, has been shown to destroy not only hematopoietic but also endothelial and epithelial tissues.131 It is therefore important to know whether such tissue conversions also occur under physiologic conditions. This question seems irrelevant if the ultimate purpose is to use somatic stem cells in tissue replacement therapies. However, knowledge about existing cellular processes might well be useful in guiding the development of tissue replacement protocols. In principle, tissue conversions might occur during embryonic development, involving the migration of hematopoietic cells from the yolk sac, aorta/gonad/mesonephros (AGM), or fetal liver to the anlagen of nonh
