Fig. 9. Possible mechanisms of sphingolipid action during Drosophila development. Sphingolipids have a diverse repertoire of cellular effects depending on cell type. This is due to the diversity of downstream effectors, including both intracellular targets and G-protein-coupled receptors, and to the apparently antagonistic actions of different sphingolipids. The ability to rapidly interconvert these lipids provides a convenient `rheostat' to regulate cell fate (reviewed by Pyne and Pyne, 2000). In addition, sphingoid phospholipids are important components of the plasma membrane. Their long, generally saturated fatty acid moieties increase membrane rigidity and are highly concentrated in specialized rafts that serve as structural elements and have been implicated in a number of signal transduction cascades. This figure summarizes only a few of the possible mechanisms by which sphingolipid intermediates may be acting during development.