Tissue-specific expression of GTPas RalA and RalB during embryogenesis and regulation by epithelial-mesenchymal interaction.

RalA and RalB are members of the Ras-like GTP-binding protein family. To investigate if Ral GTPases play a role in development, temporal and spatial patterns of RalA and RalB gene expression were examined during embryogenesis. RalA and RalB had tissue-specific pattern of expression in developing organs. Both GTPases were expressed in endodermal derivatives in the digestive tract, kidney, mesonephros, gonad, adrenal gland, trachea, and blood vessels. RalA and RalB were also expressed in the ectodermal derivatives in the brain, spinal cord, ganglia, eye, skin, hair, whiskers, and teeth. RalA and RalB were also expressed in some mesodermal tissues including the lung mesenchyme and myocardium. Tissue recombination experiments showed that of Ral expression was increased by epithelial-mesenchymal interaction in the lung, indicating that Ral expression is functionally regulated. These data identify that RalA and RalB as inducible GTPases in the developing embryo.