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. Author manuscript; available in PMC: 2016 Aug 17.
Published in final edited form as: Curr Biol. 2015 Aug 6;25(16):2099–2110. doi: 10.1016/j.cub.2015.06.076

Figure 7. Schematic Depicting the Cellular Origin and Genetic Requirements for Head Muscle, Ventral Head Vasculature, and Heart Formation.

Figure 7

(A) At 16 hpf (14 ss), nkx2.5+-only cells (yellow) are sandwiched between anterior and posterior domains of tcf21+ only cells (blue). nkx2.5+/tcf21+ cells (green) are found at the interface of the nkx2.5+ and tcf21+ domains, where these two domains overlap. Anterior tcf21+ and nkx2.5+/tcf21+ populations will give rise to the mesodermal cores of pharyngeal arches (PAs) 1 and 2, while posterior tcf21+ and nkx2.5+/tcf21+ populations will form the mesodermal cores of PAs 3–7. nkx2.5+/tcf21+ cells from the anterior domain will give rise mostly to the ventral head muscles derived from PAs 1–2 and the hypobranchial artery (HA), while nkx2.5+/tcf21+ cells from the posterior domain will give rise mostly to the ventral head muscles derived from PAs 3–7 and the posterior pharyngeal arch arteries 3–6 (pPAAs). tcf21+ cells from the anterior domain will give rise to dorsal and some ventral head muscles from PAs 1–2, while tcf21+ cells from the posterior domain will give rise to dorsal and some ventral head muscles from PAs 3–7. nkx2.5+ cells will give rise to the heart and pericardium. Dorsal view.

(B) As the PAs form, tcf21+ and nkx2.5+/tcf21+ cell clusters are found at the centers of each developing arch. tcf21+ cells predominate at the anterior and dorsal ends of PA1, the dorsal portions of PAs 2–6, and the dorsal and posterior portions of PA 7. nkx2.5+/tcf21+ cells predominate in the ventral portions of the developing arches. nkx2.5+ cells are found medially in the developing heart tube as well as laterally in the developing pericardium. Dorsal view.

(C) Top: tcf21+ cells give rise to dorsal muscles derived from PAs 1 to 7, as well as some ventral muscle fibers from PA 1 and PA 7. nkx2.5+/tcf21+ cells give rise to the ventral muscles as well as some dorsal muscle fibers of PAs 1–7. Eye and neck muscles are derived from non-nkx2.5/non-tcf21 cells (black). Bottom: nkx2.5+ cells give rise to the heart. nkx2.5+/tcf21+ cells give rise to the HA, pPAAs 3–6, and the ventral aorta (VA). Pharyngeal arch artery 1 (PAA1), the opercular artery (ORA), and much of the LDA derive from non-nkx2.5-/non-tcf21 cells (white). Part of the early LDA is derived from tcf21+ cells (data not shown). Lateral view.

(D) Top: nkx2.5–/–; tcf21 –/– embryos lose most PA-derived muscles, with some fibers from PA 1- and PA 7-derived muscles remaining. Bottom: the HA is missing in nkx2.5 –/– embryos. pPAAs 3–6 are present but are now derived from compensating non-nkx2.5/non-tcf21 cells originating in the dorsal head vasculature. Lateral view.