Defining Regulators of Self-Renewal in Hematopoietic Stem Cells Using High Throughput Genetic Screens

Group Members: Christine Glanz, Aurélie Baudet, Lina Jansson, Evan Reed and Jonas Larsson

Main Research Topics

Hematopoiesis is maintained by a small number of hematopoietic stem cells (HSCs) that can self-renew and differentiate into all hematopoietic lineages. HSCs have been used therapeutically in the clinic for several decades in life-saving treatment of malignant diseases and hematological disorders through continuously improved bone marrow (BM) transplantation protocols. Insufficient stem cell numbers are, however, a significant constraint in many settings of both autologous and allogeneic BM transplantation. Expansion of HSCs outside the body has, therefore, for many years been one of the most desired, yet elusive goals in experimental hematology and transplantation medicine.

The main objectives of our research are

• To systematically, in a high throughput fashion, identify and characterize regulators of self-renewal in murine HSCs
• To define strategies for stem cell expansion applicable in settings of clinical bone marrow transplantation and gene therapy

We have developed a genetic screening methodology in HSCs based on RNA interference (RNAi) and large short hairpin RNA (shRNA) retroviral vector libraries. Large numbers of HSCs from mice are transduced with the shRNA libraries and we screen these cells in a pooled fashion for enhanced self-renewal using positive selection assays for HSC activity in vitro and in vivo. To date, several genes with known functions in growth control and tumor suppression, in addition to unknown genes, have been retrieved in independent screens and functionally validated
Candidate genes identified from the screening experiments are characterized in detail for their role in regulation of HSCs in vitro and in vivo and tested using strategies for stem cell expansion.
We hope that these studies will reveal new gene targest for HSC expansion and thus lead to significant improvements of current bone marrow transplantation therapies.

Selected Recent and Key Publications

1. Larsson J. Scadden D. Nervous activity in a stem cell niche. Cell 2006 Jan 27:124(2):253-5
2. Larsson J, 5Karlsson S. The role of Smad signaling in hematopoiesis. Oncogene 2005 Aug 29;24(37):5676-92.
3. Larsson J , Blank U, Klintman J, Magnusson M, Karlsson S. Quiescence of hematopoietic stem cells and maintenance of the stem cell pool is not dependent on TGF-beta signaling in vivo. Exp. Hematol. 2005 May;33(5):592-6.
4. Larsson J, Blank U, Helgadottir H, Bjornsson JM, Ehinger M, Goumans MJ, Fan X, Leveen P, Karlsson S. TGF-beta signaling-deficient hematopoietic stem cells have normal self-renewal and regenerative ability in vivo despite increased proliferative capacity in vitro. Blood 2003 Nov 1;102(9):3129-35.
5. Larsson J , Goumans MJ, Sjostrand LJ, van Rooijen MA, Ward D, Leveen P, Xu X, ten Dijke P, Mummery CL, Karlsson S. Abnormal angiogenesis but intact hematopoietic potential in TGF-beta type I receptor-deficient mice. EMBO J. 2001 Apr 2;20(7):1663-73.

Collaborators

• Steve Elledge and Guang Hu, Dep. of Genetics, Harvard Medical School, Boston, MA
• Nir Hacohen, Broad Institute, Boston, MA
• David Scadden, MGH Center for Regenerative Medicine, Harvard Medical School, Boston, MA

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