Genetic dissection of blood cell production and function
Genetics tools such as specific gene knockouts or subtly modified alleles are used to probe physiological gene function and, in collaboration with colleagues Professor Doug Hilton and Benjamin Kile in the Division of Molecular Medicine, large scale ENU mutagenesis screens are in place for discovery of new blood cell controlling genes.
The process of blood cell formation, or haematopoiesis, is a dynamic system responsible for production of blood cells throughout life. Intricately controlled to allow precise numerical replacement of the billions of blood cells used every day of normal life, the haematopoietic system is also capable of rapid blood cell production in times of acute need, such as infection or severe bleeding. When these regulatory systems break down, health is compromised: the production of too few or ineffective blood cells can result in anaemia, susceptibility to infection or bleeding and conversely, production of too many or overactive cells can lead to leukaemia, inflammation or autoimmune disease. Understanding the molecules that regulate blood cell production and function has already led to major advances in treating and preventing disease and further advances will continue improve the outlook of patients with diseases of the blood. The Laboratory’s recent focus has been in two major areas of blood cell regulation: production of megakaryocytes and platelets, and control of haematopoietic stem cells.
The blood platelets are small cell fragments produced from specialized cells in the bone marrow called megakaryocytes. Platelets are necessary for blood clotting and situations in which platelet numbers are abnormally low (called thrombocytopenia), such as in some autoimmune diseases or in cancer patients receiving chemotherapy, there is a risk of serious haemorrhage. A major focus of the Laboratory is the use of genetics to define the molecular regulators of megakaryocyte and platelet production. Our knockout studies of the gene encoding c-Mpl, the receptor for thrombopoietin (TPO) contributed to defining the key role of TPO in maintaining normal circulating platelet numbers.
Over recent years we have used ENU mutagenesis in large-scale screens for regulators of platelet number and isolated over 30 mutations affecting this process. Wild-type screens have yielded new models of thrombocytopenia and mutagenesis on a genetically low platelet background has been used to search for mutations that cure thrombocytopenia, in an effort to streamline discovery of novel therapeutic targets. This suppressor screen has yielded multiple alleles that increase platelet numbers in thrombocytopenia including mutations in the genes encoding the components of the c-Myb/p300 transcriptional regulatory complex, and Suz12, an epigenetic regulator.
We have also undertaken sensitized genetic screens for regulators of stem cell function. Since compensatory mechanisms can overcome stem cell deficits allowing production of normal numbers of mature blood cells, mutations affecting stem cells may not always be evident in the blood. We reasoned that genetic screens on a stem cell-sensitized genetic background might overcome this compensation. Indeed, using this approach, we have isolated the first loss of function allele of the transcription factor Erg in a pedigree with multi-lineage haematopoietic deficiencies emanating from profound stem cell defects.
Our ongoing analyses of the mutant alleles and pedigrees emerging from these mutagenesis screens provide unique opportunities to make novel biological and molecular insights into the regulation of blood cell production and function in health and disease.