The role of Tenascin C in the lymphoid progenitor cell niche.

Hemopoietic stem cells (HSCs) are extrinsically controlled by the bone marrow (BM) microenvironment. Mice devoid of the extracellular matrix molecule Tenascin-C (TNC) were reported to develop normally. The current study explores the relationship between TNC and hemopoiesis, from HSCs within their niche to maturing progenitors in alternate niches. Although the absence of TNC did not alter the size of the BM stem cell pool, we report decreased thymic T cell progenitors with redistribution to other lymphoid organs, suggesting an anchoring role for TNC. TNC did not play an essential role in stem and progenitor cell homing to BM, but significantly altered lymphoid primed progenitor cell homing. These cells express the TNC receptor, integrin α9β1, with the same reduced homing evident in the absence of this integrin. The absence of TNC also resulted in an increased proportion and number of mature circulating T cells. In addition, the absence of TNC significantly impaired hemopoietic reconstitution after transplant and increased stem and progenitor cell mobilization. In summary, our analysis revealed unidentified roles for TNC in hemopoiesis: in lineage commitment of thymic T cell progenitors, peripheral T cell migration, and hemopoietic reconstitution.