Fig. 3. Expression of vgo/tbx1 during zebrafish embryogenesis. (A) Animal pole view. (B-E,G) Dorsal views and (F,H-L) lateral views. (A) In a shield stage embryo (6 hpf), expression is confined to the hypoblast cells of the shield (arrow) and flanking region. (B) Six-somite stage (12 hpf). Expressing cells are now organized into the cranial paraxial mesoderm (thin lateral stripe, marked by an arrowhead) and a more medial group of mesenchyme cells consisting of prospective pharyngeal endodermal cells and cells of parachordal mesoderm (arrow). (C) Ten-somite stage (14 hpf). New expression commences within the otic placode (arrow). (D) Twenty-somite stage (19 hpf). vgo/tbx1-expressing cells are now organized into the primordia of the pharyngeal arches (p1-p7). OV, otic vesicle. (E) 27 hpf. vgo/tbx1 expression within the mesodermal core and endodermal epithelia of individual arches. Anterior towards the left. (F) Lateral view of vgo/tbx1 expression in a 30 hpf embryo. In the anterior arches, the mesodermal core is in focus. In the posterior arches, the endodermal pouches are visible. (G) Horizontal section through the pharyngeal region of a 36 hpf embryo. The endodermal pouches (e) and mesodermal cores (m) of the arches are clearly vgo/tbx1 positive. (H,I) tbx1 is expressed in pharyngeal arch muscles. (H) At 48 hpf, vgo/tbx1 is expressed in most of the pharyngeal arch muscles that also express myod (I). (J-L) High magnification views of vgo/tbx1 expression within the otic vesicle. (J) 24 hpf. (K) 48 hpf. (L) 72 hpf. Expression is initially found throughout the otic vesicle except for the anteroventral corner (arrow in J). Strong expression is maintained in the developing cristae (asterisks in K,L) and semicircular canals (arrows in K,L). ah, adductor hyoideus; am, adductor mandibulae; ih, interhyoideus; hh, hyohyoideus; ima, intermandibularis anterior; imp, intermandibularis posterior; sh, sternohyoideus; tv, transversus ventralis.

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