FishFace

By 28 hpf, pharyngeal arches 1 and 2 (pa1, pa2) have begun to converge (narrow) along the anterior-posterior axis and extend (lengthen) along the dorsal-ventral axis compared with the dimensions of these axes at 24 hpf. The contact between ventral cells of pharyngeal arches 1 and 2 grows as the arches extend along the dorsal-ventral axis. Pharyngeal pouch 1 (pp1), which is GFP-negative in fli1a:EGFP transgenic fish, maintains the dorsal separation between pharyngeal arches 1 and 2. The oral ectoderm (oe), which also is GFP-negative in fli1a:EGFP transgenic fish, continues to separate dorsal and ventral cells in the anterior region of pharyngeal arch 1.