Role of cytokines and extracellular matrix in the regulation of haemopoietic stem cells

The understanding of molecular mechanisms regulating the formation, growth and differentiation of haemopoietic stem cells has advanced considerably re cently. Particular progress has been made in defining the cytokines, chemok ines and extracellular matrix components which retain and maintain primitiv e haemopoietic cell populations in bone marrow. Furthermore, signal transdu ction pathways that are critical for haemopoiesis, both in vivo and in vitr o, and that are activated by cytokines have also been identified and furthe r characterised. The importance of these processes has, this year, been exe mplified by the phenotypes of mice deficient in key signal transduction pro teins and the discovery that mutations in the component proteins of some si gnalling pathways are linked to human diseases. Significant advances in und erstanding the molecular mechanisms for mobilisation of stem cells from bon e marrow have also been made this year; this has potential importance for b one marrow transplantation.