Cystic fibrosis transmembrane conductance regulator (CFTR) regulates embryonic organizer formation during zebrafish early embryogenesis

Cystic fibrosis (CF) is associated with the manifestation of a number of medical conditions throughout the body. This prompted us to investigate the etiology of CF from the viewpoint of the embryonic organizer, which is responsible for steering the movement of surrounding cells into specific organs and tissues. In our previous work, we found that a cftr mutant had decreased nuclear β-catenin levels in the early embryo at 5 hours post-fertilization (hpf), when the organizer forms. It is known that nuclear β-catenin signaling is essential for the induction of the dorsal organizer. Therefore, we explored the role of cftr in the formation of the embryonic organizer in this work. Indeed, the expression of organizer and germ layer markers was significantly affected in cftr mutant embryos dependent on Wnt/β-catenin signaling. Furthermore, quantitative proteome analysis revealed that the cftr mutant induced significant alteration in the expression of proteins related to many critical biological processes, cellular components, molecular functions, and signaling pathways, except for the Wnt/β-catenin pathway. These findings demonstrate the function of cftr in embryonic organizer formation and provide an explanation for why many abnormalities occur in the bodies of CF patients.

Self-regulation of the head-inducing properties of the Spemann organizer

The Spemann organizer stands out from other signaling centers of the embryo because of its broad patterning effects. It defines development along the anteroposterior and dorsoventral axes of the vertebrate body, mainly by secreting antagonists of growth factors. Qualitative models proposed more than a decade ago explain the organizer’s region-specific inductions (i.e., head and trunk) as the result of different combinations of antagonists. For example, head induction is mediated by extracellular inhibition of Wnt, BMP, and Nodal ligands. However, little is known about how the levels of these antagonists become harmonized with those of their targets and with the factors initially responsible for germ layers and organizer formation, including Nodal itself. Here we show that key ingredients of the head-organizer development, namely Nodal ligands, Nodal antagonists, and ADMP ligands reciprocally adjust each other’s strength and range of activity by a self-regulating network of interlocked feedback and feedforward loops. A key element in this cross-talk is the limited availability of ACVR2a, for which Nodal and ADMP must compete. By trapping Nodal extracellularly, the Nodal antagonists Cerberus and Lefty are permissive for ADMP activity. The system self-regulates because ADMP/ACVR2a/Smad1 signaling in turn represses the expression of the Nodal antagonists, reestablishing the equilibrium. In sum, this work reveals an unprecedented set of interactions operating within the organizer that is critical for embryonic patterning.