| The objective of this thesis has been to investigate the results of combined deficiencies of the 5' inositol phosphatase SHIP and the 3' inositol phosphatase Pten in the murine immune and hematopoietic systems. SHIP and Pten act as negative regulators of the phosphatidylinositol 3-kinase (PI3K) pathway, by dephosphorylating the second messenger PIP3 to form PI(3,4)P 2 and PI(4,5)P2 respectively. Their role in regulating a common substrate while generating different products, suggests that Pten and SHIP may have both overlapping and distinct roles relating to cell signaling. The generation of mice deficient for these molecules previously revealed similarities and differences in phenotypes. These results represent the first examination of combined deficiencies of these molecules in an animal model system.; The effects of combined deficiencies of these two molecules were examined in two ways. First, the generation and characterization of mice heterozygous for both Pten and SHIP revealed co-operativity between these molecules in the generation of autoimmune characteristics. Double heterozygotes showed increased immunoglobulin levels, higher autoantigen reactivity, and more severe immune-mediated kidney damage than did wild-type and singly-heterozygous controls. Additionally, further studies of heterozygous mice revealed heightened T cell responses to antigenic challenge in vivo, and increased cytokine production upon T cell stimulation in vitro. These results suggested the requirement for threshold levels of these phosphatases in the control of immune responses, and also illustrated that partial deficiencies in genes in the same pathway can play a role in the development of multigenic diseases such as autoimmunity. Secondly, the generation of Pten +/-SHIP-/- mice revealed a previously unappreciated role for Pten in hematopoiesis, in that the phenotype of these mice manifested more severely than in SHIP-/- controls. Pten +/-SHIP-/- mice exhibited unique peripheral blood abnormalities, altered functional behavior of committed progenitor cells, a more severe B cell developmental defect and a defect in multilineage repopulation of irradiated recipients, providing the first evidence that Pten and SHIP act cooperatively to maintain homeostasis in the hematopoietic system.; Together, these results highlight the importance of regulation of the PI3K pathway in immune responses and hematopoiesis, and support cooperative roles for both Pten and SHIP in these processes. |
