Mutations in Bcl9 and Pygo genes cause congenital heart defects by tissue-specific perturbation of Wnt/ß-catenin signaling.

Bcl9 and Pygopus (Pygo) are obligate Wnt/ß-catenin cofactors in Drosophila, yet their contribution to Wnt signaling during vertebrate development remains unresolved. Combining zebrafish and mouse genetics, we document a conserved, ß-catenin-associated function for BCL9 and Pygo proteins during vertebrate heart development. Disrupting the ß-catenin-BCL9-Pygo complex results in a broadly maintained canonical Wnt response yet perturbs heart development and proper expression of key cardiac regulators. Our work highlights BCL9 and Pygo as selective ß-catenin cofactors in a subset of canonical Wnt responses during vertebrate development. Moreover, our results implicate alterations in BCL9 and BCL9L in human congenital heart defects.

Cre/lox-controlled spatiotemporal perturbation of FGF signaling in zebrafish.

BACKGROUND: Spatiotemporal perturbation of signaling pathways in vivo remains challenging and requires precise transgenic control of signaling effectors. Fibroblast growth factor (FGF) signaling guides multiple developmental processes, including body axis formation and cell fate patterning. In zebrafish, mutants and chemical perturbations affecting FGF signaling have uncovered key developmental processes; however, these approaches cause embryo-wide perturbations, rendering assessment of cell-autonomous vs. non-autonomous requirements for FGF signaling in individual processes difficult. RESULTS: Here, we created the novel transgenic line fgfr1-dn-cargo, encoding dominant-negative Fgfr1a with fluorescent tag under combined Cre/lox and heatshock control to perturb FGF signaling spatiotemporally. Validating efficient perturbation of FGF signaling by fgfr1-dn-cargo primed with ubiquitous CreERT2, we established that primed, heatshock-induced fgfr1-dn-cargo behaves similarly to pulsed treatment with the FGFR inhibitor SU5402. Priming fgfr1-dn-cargo with CreERT2 in the lateral plate mesoderm triggered selective cardiac and pectoral fin phenotypes without drastic impact on overall embryo patterning. Harnessing lateral plate mesoderm-specific FGF inhibition, we recapitulated the cell-autonomous and temporal requirement for FGF signaling in pectoral fin outgrowth, as previously inferred from pan-embryonic FGF inhibition. CONCLUSIONS: As a paradigm for rapid Cre/lox-mediated signaling perturbations, our results establish fgfr1-dn-cargo as a genetic tool to define the spatiotemporal requirements for FGF signaling in zebrafish. Developmental Dynamics 247:1146-1159, 2018. © 2018 Wiley Periodicals, Inc.