Origin and development of haematopoietic cells

The development of new treatment strategies ofhaematopoietic stem cell (HSC) transplantation for a large number of non-malignant and malignant diseases has again led to an increasing interest in investigation of HSC biology, especially of molecular mechanisms responsible for the formation and development of haematopoietic tissue. During the last decade a number of experimental models have been introduced to investigate the nature of the HSC. One of the most popular models is in vitro differentiation of embryonic stem (ES) cells. The analysis of ES cells with targeted gene disruption is a new approach in the identification of genes that play a key role in the establishment of hematopoiesis. The most important advantage of this strategy is the possibility to investigate the function of the genes whose mutations cause death of embryo. Applied in vivo, the technology of mutated ES forms a basis for creation and investigation of "knock-out gene" animals. In combination with transgenic animals, this model has revealed a group of genes encoding transcription factors that play the key role in the development and differentiation of haematopoietic tissue. The purpose of the first part of this review is to make the reader familiar with recent results of haematopoietic stem cell studies in vivo and in vitro. In the second part attention of the reader is focused on molecular mechanisms that control hematopoiesis, especially transcription factors.