Fig. 3.

Depletion of Neur results in defective apical constriction. a Cross-section view of a GFP-Neur embryo showing apical accumulation of Neur (GFP, green; four copies of the BAC transgene; n = 2 experiments) in ventral cells during furrow formation. b deGradFP strategy: GFP-Neur (green) was targeted for degradation using a Cullin-based E3 ubiquitin ligase complex via an anti-GFP nanobody (blue). c, d Cross-section views of wild-type (c) and neur ^degrad (d) embryos. In wild-type embryos (c), Dl accumulates into endocytic vesicles specifically in the mesoderm. In 60% of the neur ^degrad embryos (n = 35), Dl was mostly detected at the membrane, indicative of a strong Neur depletion (d). e Live imaging of a neur ^degrad embryo expressing Gap43-Cherry (white; ventral cells in blue, tracking in red). A delay in furrow formation was observed. f Apical constriction (quantified as in Fig. 1f) was delayed in neur ^degrad embryos relative to wild-type embryos (red). Intermingled constricting and non-constricting cells were observed ventrally (Supplementary Fig. 4l). g–j Ventral cell lengthening was measured prior to furrow formation (stage I, as defined in Sweeton et al.⁵; n = 3 experiments) in wild-type (g, h; n = 9), in neur ^degrad (g, i; n = 5) and sna>Brd ^R embryos (g, j; n = 14) stained for Nrt (h–j) and Dl (h, i), or ectopic Brd^R (j; HA epitope). Ectopic Brd accumulated at the apical cortex and in cytoplasmic dots (j). Lengthening increased upon inhibition and depletion of Neur (g)