Fig. 1.

Apoptotic elimination of unfit cells smoothens the Wnt/β-catenin gradient. a Schematic illustration of Wnt/β-catenin activity gradient formation. A: anterior, P: posterior. b Caspase-3 activation in unfit cells with abnormal Wnt/β-catenin activity. Whole-mount immunostaining of d2EGFP (green) and active caspase-3 (magenta) in Tg(OTM:d2EGFP) zebrafish embryos (Dorsal view). Dotted line indicates abnormal Wnt/β-catenin-reporter activity. Scale bars, 200 μm. c OTM:ELuc-CP drives destabilized ELuc-CP expression in response to Wnt/β-catenin signalling activation in reporter embryo (dorsal view). Scale bar, 200 μm. (See also Supplementary Movie 1). d Time lapse images showing unfit cells with abnormal Wnt/β-catenin activity appear then disappear in OTM:ELuc-CP embryos. Scale bars, 100 μm. Pixel area length is 6.5 μm, ≤ zebrafish deep cell diameter (~10 μm). e Physiological Wnt/β-catenin-noise during zebrafish AP axis formation. Graphs show the number of pixels with unfit Wnt/β-catenin activity in the luminescence images of living OTM:ELuc-CP transgenic zebrafish embryos during AP axis formation. Schematic illustrations: pixel retaining >two-fold or <two-fold intensity compared to neighbouring pixels for ≥frames (>6 min) was defined as High or Low noise, respectively. Pixels retained for ≥two frames were counted as the physiological Wnt/β-catenin noise. Pixels spontaneously showing abnormally high or low activity within one frame were regarded as other noise (e.g., cosmic rays and detector noises) and excluded. f Apoptosis inhibition enhances unfit abnormally high or low Wnt/β-catenin activity cell appearance. Whole-mount in situ hybridization of d2EGFP in Tg(OTM:d2EGFP) embryos (dorsal view). p < 0.01 (Fisher’s exact test). Scale bar, 200 μm. See also Supplementary Figs. 1 and 2