Cyp26b1 function before 60 hpf is necessary for mandibulohyoid junction formation.

(A,D) Embryos raised in media containing 0.01% DMSO develop normally. (B) 100% of embryos treated with talarozole between 54 and 60 hpf displayed ectopic muscle projection in the second pharyngeal arch, and the intermandibularis posterior muscles overextended in 58.3% of embryos (n = 64). (C) Among embryos treated from 60 to 72 hpf, 76.9% had mild ectopic muscle projections, but 96.2% developed normal tendon and end-to-end muscle connections at the mandibulohyoid junction (n = 26). (E,F) Talarozole-treated embryos recapitulated cyp26b1 mutant skeletal phenotypes of Meckel’s cartilage fusion (red arrowheads and insets), ceratohyal fusion (black arrowheads and insets), and basihyal reduction (arrows). All images ventral view, anterior to the left. Scale bar = 50 μm.