RAPID COMMUNICATION Stromal Expression of Jagged 1 Promotes Colony Formation by Fetal Hematopoietic Progenitor Cells

The Notch signaling system regulates proliferation and differentiation in many tissues. Notch is a transmembrane receptor activated by ligands expressed on adjacent cells. Hematopoietic stem cells and early progenitors express Notch, making the stromal cells which form cell-cell contacts with progenitor cells candidate ligand-presenting cells in the hematopoietic microenvironment. Therefore, we examined primary stromal cell cultures for expression of Notch ligands. Using reverse transcription-polymerase chain reaction, in situ hybridization, immunohistochemistry, and Western blot-ting, we demonstrate expression of Jagged 1 in primary stromal cultures. To investigate if the stromal expression of Jagged 1 has functional effects on hematopoietic progeni-tors, we cultured CD341, c-kit1 hematopoietic progenitor cells derived from the aorto gonadal mesonephros region o