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. Author manuscript; available in PMC: 2021 Jul 1.
Published in final edited form as: Curr Top Dev Biol. 2020 Nov 19;143:1–36. doi: 10.1016/bs.ctdb.2020.09.005

Figure 2. Fkh mediated morphogenetic events in SG tube formation and positioning.

Figure 2.

(A) Fkh activates expression of Fog to initiate the molecular/cellular events of apical constriction. Hkb is proposed to localize Fog secretion (and potentially the localization of its yet-to-be characterized GPCR receptor) to the apical surface. Basally-localized RhoGAPs may also help localize Rho activation to the apical domain. (B) Fkh, along with Rib, transcriptionally elevate Crb expression within the SG primordia. The high-levels of transmembrane Crb in membranes shared between SG cells versus membranes between SG cells and their non-SG neighbors preferentially localizes active Rok to the external boundary membrane of the SG, leading to the formation of a supracellular myosin cable surrounding the entire SG. (C) Based on the severity of SG morphological phenotypes associated with loss of fkh versus loss of Crb or of fog, it is proposed that Fkh is also involved in cell rearrangement. (D) Collective migration is required for the correct final position of the SG within the embryo. A number of signaling pathways are required for migration and navigation of the SG. How these pathways fit into the transcriptional network controlling morphogenesis awaits discovery.