Bmp signaling maintains a mesoderm progenitor cell state in the mouse tailbud

Caudal somites are generated from a pool of progenitor cells located in the tailbud region. These progenitor cells form the presomitic mesoderm that gradually differentiates into somites under the action of the segmentation clock. The signals responsible for tailbud mesoderm progenitor pool maintenance during axial elongation are still elusive. Here, we show that Bmp signaling is sufficient to activate the entire mesoderm progenitor gene signature in primary cultures of caudal mesoderm cells. Bmp signaling acts through the key regulatory genes brachyury (T) and Nkx1-2 and contributes to the activation of several other regulators of the mesoderm progenitor gene network. In the absence of Bmp signaling, tailbud mesoderm progenitor cells acquire aberrant gene expression signatures of the heart, blood, muscle and skeletal embryonic lineages. Treatment of embryos with the Bmp inhibitor noggin confirmed the requirement for Bmp signaling for normal T expression and the prevention of abnormal lineage marker activation. Together, these results identify Bmp signaling as a non-cell-autonomous signal necessary for mesoderm progenitor cell homeostasis.