Jun is required in Isl1-expressing progenitor cells for cardiovascular development.

Jun is a highly conserved member of the multimeric activator protein 1 transcription factor complex and plays an important role in human cancer where it is known to be critical for proliferation, cell cycle regulation, differentiation, and cell death. All of these biological functions are also crucial for embryonic development. Although all Jun null mouse embryos die at mid-gestation with persistent truncus arteriosus, a severe cardiac outflow tract defect also seen in human congenital heart disease, the developmental mechanisms are poorly understood.

Ablation of specific expression domains reveals discrete functions of ectoderm- and endoderm-derived FGF8 during cardiovascular and pharyngeal development.

Fibroblast growth factor 8 (Fgf8) is expressed in many domains of the developing embryo. Globally decreased FGF8 signaling during murine embryogenesis results in a hypomorphic phenotype with a constellation of heart, outflow tract, great vessel and pharyngeal gland defects that phenocopies human deletion 22q11 syndromes, such as DiGeorge. We postulate that these Fgf8 hypomorphic phenotypes result from disruption of local FGF8 signaling from pharyngeal arch epithelia to mesenchymal cells populating and migrating through the third and fourth pharyngeal arches.