Gene expression profile of cells with unfit Wnt morphogen gradient during cell competition

Morphogen signalling forms an activity gradient and instructs cell identities in a signalling strength-dependent manner to pattern developing tissues. However, developing tissues also undergo dynamic morphogenesis, which may produce cells with unfit morphogen signalling and consequent noisy morphogen gradient. Here we show that a cell competition-related system corrects such noisy morphogen gradients. Zebrafish imaging analyses of the Wnt/ß-catenin signalling gradient, which acts as a morphogen to establish embryonic anterior-posterior patterning, revealed that unfit cells with abnormal Wnt/ß-catenin activity spontaneously appear and produce noise in the gradient. Communication between unfit and neighbouring fit cells via cadherin proteins stimulates apoptosis of the unfit cells by activating Smad signalling and reactive oxygen species production. This unfit cell elimination is required for proper Wnt/ß-catenin gradient formation and consequent anterior-posterior patterning. Because this gradient controls patterning not only in the embryo but also in adult tissues, this system may support tissue robustness and disease prevention. Overall design: ß-catCA (constitutive active form of ß-catenin)-expressing cells from ß-catCA-mosaically introduced or ß-catCA ubiquitously-expressing zebrafish early embryos, or cells from uninjected zebrafish embryos were sorted by FACS cell sorter. Total RNAs were extracted and analyzed by RNA-seq.