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. Author manuscript; available in PMC: 2020 Dec 1.
Published in final edited form as: Gene Expr Patterns. 2019 Oct 24;34:119077. doi: 10.1016/j.gep.2019.119077

Figure 3. Armh4 is expressed in second heart field and its derivatives.

Figure 3.

(A,B) Wholemount in situ hybridization of E9 embryo (A, frontal view; B, right side view) reveals Armh4 is expressed throughout the heart and SHF (white arrow, B) but is expressed at lower levels in the left ventricle (black arrow, B). However, Armh4 expression is absent from the yolk sac (Ys). (C) Armh4 is robustly expressed in E9.5 SHF (black arrow) and OFT (white arrow) but only weakly expressed in the left ventricle and atria. Armh4 is also expressed in the head, posterior to the forebrain (*). (D) Serial sections through heart region in panel C, counterstained with eosin. Armh4 is localized to the OFT outer myocardial layer, the right ventricle and atria, the SHF (arrows) and the right sinuous venous (rsv), but is absent in the foregut endoderm. (E-G) At E10.5 (E, left; F, right; G, frontal views) Armh4 is only robustly expressed in the SHF (white arrows in E,F; black arrows in G) and right ventricle. Armh4 in the cranial region persists and is also present in trigeminal ganglia (* in F). (H) Serial section in situ hybridization analysis confirmed Armh4 mRNA in the SHF extends from the branchial arches all the way down along the OFT and arterial chamber wall to the septum transversum below the heart (arrows). (I,J) Armh4 section in situ hybridization (I) and MF20 expression (J) in adjacent transverse E10.5 embryo sections. Note Armh4 mRNA and MF20 protein overlap in the OFT cardiomyocyte outer layer and right ventricle (rv) cardiomyocytes, but Armh4 extends further into the branchial arch/SHF region (arrows, I) that is negative for MF20 (arrows, J). (K) Armh4 section in situ hybridization in transverse E11 embryos confirms Armh4 is expressed throughout the proximal pharyngeal arch/SHF region (arrowhead), SHF, and OFT and predominantly right ventricular cardiomyocytes. Note Armh4 mRNA is absent from the early OFT endocardial cushions (*). (L) A single representative example of serial sections through E12.5 wholemount Armh4 stained embryo, counterstained with eosin. Armh4 is localized to the OFT outer myocardial layer, the right ventricle and right atria, but is absent from endocardial cushions (*). (M) Section in situ hybridization of transverse E13 embryo reveals Armh4 is expressed in the OFT and right ventricular cardiomyocytes (arrows) but is absent from both the conal and truncal endocardial cushions (*). Armh4 is also present in the maxillar and lateral nasal process (arrowheads). Scale bars: D,K=20μm; F, H-J,L=50μm. Abbreviations: Ao, ascending aorta; ba, branchial arch; Oft, outflow tract; fore, foregut; la, left atria; lv, left ventricle; pul, pulmonary trunk; ra, right atria.