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The second heart field ( SHF), foregut endoderm and sonic hedgehog ( SHH) signaling pathway are all reported to associate with normal morphogenesis and septation of outflow tract ( OFT). However, the morphological relationships of the development of foregut endoderm and expression of SHH signaling pathway members with the development of surrounding SHF and OFT are seldom described. In this study, serial sections of mouse embryos from ED9 to ED13 (midgestation) were stained with a series of marker antibodies for specifically highlighting SHF (Isl-1), endoderm (Foxa2), basement membrane (Laminin), myocardium ( MHC) and smooth muscle ( α- SMA) respectively, or SHH receptors antibodies including patched1 (Ptc1), patched2 (Ptc2) and smoothened, to observe the spatiotemporal relationship between them and their contributions to OFT morphogenesis. Our results demonstrated that the development of an Isl-1 positive field in the splanchnic mesoderm ventral to foregut, a subset of SHF, is closely coupled with pulmonary endoderm or tracheal groove, the Isl-1 positive cells surrounding pulmonary endoderm are distributed in a special cone-shaped pattern and take part in the formation of the lateral walls of the intrapericardial aorta and pulmonary trunk and the transient aortic-pulmonary septum, and Ptc1 and Ptc2 are exclusively expressed in pulmonary endoderm during this Isl-l positive field development, suggesting special roles played in inducing the Isl-l positive field formation by pulmonary endoderm. It is indicated that pulmonary endoderm plays a role in the development and specification of SHF in midgestation, and that pulmonary endoderm-associated Isl-l positive field is involved in patterning the morphogenesis and septation of the intrapericardial arterial trunks. [ABSTRACT FROM AUTHOR]

The second heart field ( SHF) is indicated to contribute to the embryonic heart development. However, less knowledge is available about SHF development of human embryo due to the difficulty of collecting embryos. In this study, serial sections of human embryos from Carnegie stage 10 ( CS10) to CS16 were stained with antibodies against Islet-1 (Isl-1), Nkx2.5, GATA4, myosin heavy chain ( MHC) and α-smooth muscle actin (α- SMA) to observe spatiotemporal distribution of SHF and its contribution to the development of the arterial pole of cardiac tube. Our findings suggest that during CS10 to CS12, SHF of the human embryo is composed of the bilateral pharyngeal mesenchyme, the central mesenchyme of the branchial arch and splanchnic mesoderm of the pericardial cavity dorsal wall. With development, SHF translocates and consists of ventral pharyngeal mesenchyme and dorsal wall of the pericardial cavity. Hence, the SHF of human embryo shows a dynamic spatiotemporal distribution pattern. The formation of the Isl-1 positive condense cell prongs provides an explanation for the saddle structure formation at the distal pole of the outflow tract. In human embryo, the Isl-1 positive cells of SHF may contribute to the formation of myocardial outflow tract ( OFT) and the septum during different development stages. [ABSTRACT FROM AUTHOR]