Abstract
Guided cell migration is necessary for the proper function and development of many tissues, one of which is the Drosophila embryonic salivary gland. Here we show that two distinct Wnt signaling pathways regulate salivary gland migration. Early in migration, the salivary gland responds to a WNT4-Frizzled signal for proper positioning within the embryo. Disruption of this signal, through mutations in Wnt4, frizzled or frizzled 2, results in misguided salivary glands that curve ventrally. Furthermore, disruption of downstream components of the canonical Wnt pathway, such as dishevelled or Tcf, also results in ventrally curved salivary glands. Analysis of a second Wnt signal, which acts through the atypical Wnt receptor Derailed, indicates a requirement for Wnt5 signaling late in salivary gland migration. WNT5 is expressed in the central nervous system and acts as a repulsive signal, needed to keep the migrating salivary gland on course. The receptor for WNT5, Derailed, is expressed in the actively migrating tip of the salivary glands. In embryos mutant for derailed or Wnt5, salivary gland migration is disrupted; the tip of the gland migrates abnormally toward the central nervous system. Our results suggest that both the Wnt4-frizzled pathway and a separate Wnt5-derailed pathway are needed for proper salivary gland migration.
