Abstract I-1

The EGF-like homeotic protein dlk participates in stroma-pre-B cell interactions and controls in vitro stromal cell adipogenesis and pre-B cell growth in the absence of IL-7
Steven R. Bauer, María José Ruiz-Hidalgo, Julia Goldstein and Jorge Laborda

A close relationship exists between adipocyte differentiation of stromal cells and their capacity to support hematopoiesis. The molecular basis for this is unknown. We have established an in vitro system to study whether dlk/Pref-1, an EGF-like molecule that intervenes in adipogenesis and fetal liver hematopoiesis, affects both stromal cell adipogenesis and B cell lymphopoiesis. Pre-B cell cultures require both soluble IL-7 and stromal cell to promote pre-B cell growth and prevent B cell maturation or death. We found that Balb/c 3T3 fibroblasts express dlk and function as stromal cells. Transfection of these cells with antisense dlk decreased dlk expression and increased insulin-induced adipocytic differentiation. When antisense transfectants were used as stroma, pre-B cells grew in a manner inversely correlated with the expression of stromal dlk, in the absence of IL7. In addition, pre-B and mature B cells also express dlk. These results demonstrate that dlk plays a role in regulating differentiation signals directed both to the stromal cells and to the lymphocyte precursors. Understanding of the molecular mechanisms governing stromal cell-precursor interactions is important for regulation of biological therapies involving ex vivo expansion of hematopoietic and other tissue precursors.