XB-ART-55837J Cell Biol January 1, 2019; 218 (5): 1743-1763.
GPCR-independent activation of G proteins promotes apical cell constriction in vivo.
Heterotrimeric G proteins are signaling switches that control organismal morphogenesis across metazoans. In invertebrates, specific GPCRs instruct G proteins to promote collective apical cell constriction in the context of epithelial tissue morphogenesis. In contrast, tissue-specific factors that instruct G proteins during analogous processes in vertebrates are largely unknown. Here, we show that DAPLE, a non-GPCR protein linked to human neurodevelopmental disorders, is expressed specifically in the neural plate of Xenopus laevis embryos to trigger a G protein signaling pathway that promotes apical cell constriction during neurulation. DAPLE localizes to apical cell-cell junctions in the neuroepithelium, where it activates G protein signaling to drive actomyosin-dependent apical constriction and subsequent bending of the neural plate. This function is mediated by a Gα-binding-and-activating (GBA) motif that was acquired by DAPLE in vertebrates during evolution. These findings reveal that regulation of tissue remodeling during vertebrate development can be driven by an unconventional mechanism of heterotrimeric G protein activation that operates in lieu of GPCRs.
PubMed ID: 30948426
PMC ID: PMC6504902
Article link: J Cell Biol
Genes referenced: ccdc88c crb3 ctnnb1 gba gprc6a isyna1 llgl2 myc vangl2
Article Images: [+] show captions
|Figure 4. Loss of DAPLE in Xenopus causes apical constriction defects during neurulation. (A) Whole-mount F-actin staining (magenta) of Xenopus embryos unilaterally coinjected with xDAPLE MO and a lineage tracer (mRFP or GFP-CAAX, green) showing enlarged apical surface of DAPLE-depleted neuroepithelial cells compared with uninjected control sides at stages 15 and 16. (B) Transversal cryosection stained for β-catenin (magenta) of the anterior neural plate of an embryo at stage 16 unilaterally coinjected with xDAPLE MO and a lineage tracer (GFP-CAAX, green). Outlines of cell borders are depicted in the bottom to show the lack of wedge shape morphology in the outer layer of neuroepithelial cells depleted of DAPLE. (C–F) Whole-mount pMLC2 (C), ZO-1 (D), GFP (E), and Vangl2 (F) staining (magenta) of Xenopus embryos unilaterally coinjected with xDAPLE MO and a lineage tracer (GFP-CAAX or mRFP; green). In E, embryos were bilaterally injected with Crb3-GFP (top) or GFP-Lgl2 (bottom). In F, staining for the lineage tracer (mRFP) is not shown for clarity, and an immunoblot from dissected neural plates is shown in the bottom. xDAPLE depleted sides show defective staining for actomyosin contractility and PCP markers at stage 15, while markers of apical cell junctions or apicobasal polarity are not changed. All images presented in this figure are representative results of n ≥ 3 experiments. All scale bars represent 25 µm, except those in A, which represent 50 µm.|
|Figure 7. Mechanism of G protein–mediated regulation of apical cell constriction during neurulation by the non-GPCR protein DAPLE. (A) Expression of DAPLE is specifically induced during neurulation. Upon expression, DAPLE localizes to apical cell junctions of neuroepithelial cells, where it triggers G protein activation that leads to apical cell constriction and the subsequent bending of the neural plate. (B) Theme and variations of G protein–regulated apical cell constriction during epithelial tissue morphogenesis in vertebrates versus invertebrates. Heterotrimeric G proteins are part of a conserved ubiquitous machinery that controls actomyosin contractility, but they are regulated differently across species. In vertebrates, DAPLE fulfills the role performed by GPCRs in invertebrates as tissue-specific activators of signaling that drives apical cell constriction. (C) The G protein regulatory function of DAPLE (i.e., its GBA motif) was acquired during evolution in the transition from invertebrates to vertebrates, suggesting that the unconventional mechanism of G protein activation described here is an evolutionary innovation for epithelial remodeling in vertebrates.|
References [+] :
Aittaleb, Structure and function of heterotrimeric G protein-regulated Rho guanine nucleotide exchange factors. 2010, Pubmed