Nr2f transcription factors promote the identity of the vertebrate upper jaw

The jaws are complementary in form and function but develop asymmetrically, as the lower but not upper jaw bone forms around a prominent cartilage template. How such differences in skeletal composition are patterned is unclear. Here, we identify four Nuclear receptor 2f genes, nr2f1a, nr2f1b, nr2f2, and nr2f5, as enriched in zebrafish upper jaw precursors. Whereas loss of Nr2f genes results in expansion of upper jaw cartilage to resemble that of the lower jaw, Nr2f5 misexpression inhibits lower jaw cartilage formation. Genome-wide analyses show that Nr2f genes prevent expansion of lower jaw-associated gene expression into the upper jaw territory. Further, restriction of Nr2f expression by Endothelin1 signaling is critical for lower jaw development, as reducing Nr2f dosage fully restores lower jaw development in edn1 mutants. We propose that Nr2f genes drive jaw asymmetry by limiting early cartilage differentiation in the upper jaw to preserve more precursors for later osteogenesis. Zebrafish pharyngeal arch cells expressing both fli1a:GFP and sox10:DsRed were isolated by FACS from 36 hpf nr2f2; nr2f5 double mutant embryos (2 replicates: n = 37 & 84; 18,858 & 30,655 cells), sox10:Gal4+ embryos (n = 69; 86,517 cells), sox10:Gal4; UAS:Nr2f5 embryos (n = 84; 56,866 cells).