During embryogenesis, the salivary gland (SG) primordia change geometry from two-dimensional epithelial sheets on the embryo surface into fully internalized, three-dimensional tubes. Invagination of the SG absolutely depends on the FoxA transcription factor Fork Head (Fkh). Here, we show the temporal and spatial regulation of myosin cytoskeleton during SG invagination and reveal the tissue-specific signaling pathway that regulates it. Myosin re-localizes from cortical to apicomedial region of the SG cells prior to invagination, which is dependent on Fkh. Using both live and fixed sample imaging, we revealed that these apicomedial myosin cables are pulsatile and that they provide motive forces for cell deformation and subsequent apical constriction. We also show similar temporal and spatial re-distribution of Rho kinase (Rok), which also requires the Fkh function. We further discovered that Fkh regulates the SG expression of a secreted ligand folded gastrulation (fog) and that apicomedial localization of Rok and myosin is defected in fog mutant SGs, which have a range of invagination defects. Surprisingly, unlike mesodermal tissue invagination, blocking apical constriction does not prevent the SG cells from internalizing. Instead, SGs with genetic manipulation to block apical constriction still invaginate but show abnormal tissue geometry. We also provide evidence on the putative G protein coupled receptor(s) that appear to mediate the Fog signals to the Rok and myosin.