SHP2 Regulation of the Plasticity of Bone Marrow Osterix+ Stroma

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(PLEASE KEEP IN WORD, DO NOT PDF) This section must be no longer than 30 lines of text. It has been recently reported that the promoter of the master osteogenic transcription factor, OSTERIX, is active perinatally in hematopoietic cells, and that GFP+ blood cells circulate at low frequency in Tg(Osx-GFP:Cre) reporter mice. However, nothing is currently known about the significance of the hematopoietic cell-specific OSTERIX expression, and whether OSTERIX depletion might impact hematopoiesis. The work outlined in this proposal builds on the novel findings that Osx-GFP marks some BM and peripheral blood cells, and the number of these GFP+ blood cells decreases and disappears during development and maturation. Since OSTERIX expression and function in the hematopoietic system remain largely unknown, these findings together stimulate the hypothesis that OSTERIX is temporarily expressed in hematopoietic stem cells (HSCs) and that it is required for their survival, and/or lineage commitment and hematopoietic homeostasis. To test this novel hypothesis, we propose two specific Aims. In Aim 1, we will determine the dynamics of OSTERIX expression by quantifying GFP+ blood cells in embryonic, postnatal, and adult Tg(Osx-GFP:Cre) mice using FACS analysis. In Aim 2, we will determine the impact of OSTERIX depletion in HSCs on cell survival and multilineage differentiation using Tg(Mx1-Cre;Osxfx/fx) upon p(I)(C) induction. This innovative study will result in the first-ever description of OSTERIX’s regulatory role in the hematopoietic system and provide foundational information on the effect of OSTERIX dysregulation in blood. Successful completion of the work proposed will have a significant impact on our understanding of the hematopoietic regulation by OSTERIX and advance our knowledge about OSTERIX in the extraskeletal tissues.