IDENTIFICATION AND CHARACTERIZATION OF A NOVEL LINE OF DROSOPHILA SCHNEIDER-S2 CELLS THAT RESPOND TO WINGLESS SIGNALING

Wingless (Wg) treatment of Drosophila wing disc clone 8 cells leads to Armadillo (Arm) protein elevation, and this effect has been used as t he basis of in vitro assays for Wg protein. Previously analyzed stocks of Drosophila Schneider S2 cells could not respond to added Wg, becau se they lack the Wg receptor, Dfrizzled-2. However, we found that a li ne of S2 cells obtained from another source express Dfrizzled-2 and Df rizzled-1. Thus, we designated this cell line as S2R+ (S2 receptor plu s). S2R+ cells respond to addition of extracellular Wg by elevating Ar m and DE-cadherin protein levels and by hyperphosphorylating Dsh, just as clone 8 cells do. Moreover, overexpression of Wg in S2R+, but not in S2 cells, induced the same changes in Dsh, Arm, and DE-cadherin pro teins as induced in clone 8 cells, indicating that these events are co mmon effects of Wg signaling, which occurs in cells expressing functio nal Wg receptors. In addition, unphosphorylated Dsh protein in S2 cell s was phosphorylated as a consequence of expression of Dfrizzled-2 or mouse Frizzled-6, suggesting that basal structures common to various f rizzled family proteins trigger this phosphorylation of Dsh, S2R+ cell s are as sensitive to Wg as are clone 8 cells but can grow in simpler medium. Therefore, the S2R+ cell line is likely to prove highly useful for in vitro analyses of Wg signaling.