Fig. 7

Sustained PLC activity partially rescues Msec14l3 defects.

(A) Morphological defects in zebrafish embryos treated with 1.5 μM or 3 μM U73122 from the 1 cell stage. DMSO treated group serves as a control. Scale bars, 100 μm. (B) Confocal imaging of PLCδ1-PH-mCherry (red, PIP₂ probe) shows the PM accumulation of PIP₂ in zebrafish embryos treated with 1.5 μM DMSO or 1.5 μM U73122 at 4 and 6 hpf. The first two whole embryo panels are 3D views of z-stacks, while the last panel is enlarged views of single z-stack pictures (z = 5 for both 4 hpf and 6 hpf) from regions encompassed by white boxes. Scale bars, 100 μm for the whole embryos; 25 μm for the enlarged columns. (C) Active Plcδ4a overcomes the CE defects in Msec14l3 mutants. 100 pg plcδ4a-Δ28 mRNA was used for injection. Lateral views for embryos in the first panel, dorsal views for those in the last panel. Blue and red two-way arrows indicate the width of neural plate and the length of notochord respectively. Scale bars, 100 μm. (D) Hypothetic working model of Sec14l3 participation in Wnt/Ca²⁺ signaling. In the absence of Wnt (left panel), Sec14l3 is mainly maintained in the ER and cytoplasm, forming a heterodimer with Dvl in its inactive state, Sec14l3-GDP. Upon Wnt5 stimulation (right panel), Fz/Dvl-mediated Sec14l3 is recruited to the PM and switched to the active state, Sec14l3-GTP, and subsequently promotes Plcδ4a localization from cytoplasm to the PM and then the consequent activity at least in two aspects: its PIP₂ hydrolytic activity to generate second messenger InsP₃ and DAG for signaling propagation (Ca²⁺ release and p-Erk activation); and its GAP activity to terminate Sec14l3-GTP.