Semir Somi

Developmental pattern of ANF gene expression reveals a strict localization of cardiac chamber formation in chicken.

In mouse, atrial natriuretic factor (ANF) gene expression was shown to be a marker for chamber formation within the embryonic heart. To gain insight into the process of chamber formation in the chicken embryonic heart, we analyzed the expression pattern of cANF during development. We found cANF to be specifically expressed in the myocardium of the morphologically distinguishable atrial and ventricular chambers, similar to ANF in mouse. cANF expression was never detected in the myocardium of the atrioventricular canal (AVC), inner curvature, and outflow tract (OFT), which is lined by endocardial cushions. Expression was strictly excluded from the interventricular myocardium and most proximal part of the bundle branches, as identified by the expression of Msx‐2, whereas the rest of the bundle branches, trabeculae, and surrounding working myocardium did express cANF. The myocardium that forms de novo within the cushions after looping did not express cANF. At HH9 cANF expression was first observed in a subset of cardiomyocytes, which was localized ventrally in the fused heart tube and laterally in the unfused cardiac sheets. Together, these results show that cANF expression can be used to distinguish differentiated chamber (working) myocardium, including the peripheral ventricular conduction system, from embryonic myocardium. We conclude that differentiation of chamber myocardium takes place already at HH9 at the ventral side of the linear heart tube, possibly preceded by latero‐medial signals in the unfused cardiac sheets. Anat Rec 266:93–102, 2002.

Atrial and Ventricular Myosin Heavy-chain Expression in the Developing Chicken Heart: Strengths and Limitations of Non-radioactive In Situ Hybridization

Myosin heavy-chain (MHC) isoforms are major structural components of the contractile apparatus of the heart muscle. Their spatio-temporal patterns of expression have been used as a tool to dissect cardiac development and differentiation. Although extensively investigated, controversy still exists concerning the expression patterns of atrial (AMHC), ventricular (VMHC), and cardiac myosin heavy-chain (CMHC) during development in the heart. In this study, we describe that probe length, probe concentration, and staining time in the non-radioactive in situ hybridization procedure seriously influence the observed pattern of MHC expression and the subsequent interpretation, explaining the divergent opinions in the field. Using a variety of external and internal controls for the in situ hybridization procedure, we demonstrate that both AMHC and VMHC are expressed throughout the entire heart tube during early development. During subsequent development, VMHC becomes restricted to the ventricles, whereas AMHC remains expressed in the atria, and, at substantially lower levels, is detected in the ventricles. These results are discussed in the context of methodological constraints of demonstrating patterns of gene expression. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.

Comparative analysis of the natriuretic peptide precursor gene cluster in vertebrates reveals loss of ANF and retention of CNP-3 in chicken

We identified and characterized the chicken natriuretic peptide precursor gene cluster and found its organization to be highly conserved compared with the mammalian Nppb‐Nppa cluster. However, phylogenetic analysis indicated that the putative chicken natriuretic peptide precursor genes are the homologues of CNP‐3 and Nppb, respectively. Comparative expression analysis revealed that, in human, mouse, and rat hearts, Nppb is a novel marker for the differentiating working myocardium. Its expression pattern is strikingly similar to that of Nppa before birth, and diverges only after birth. In contrast, whereas the chicken Nppb gene expression profile resembled that of mammalian Nppb, the CNP‐3 gene showed very limited expression in the heart, not resembling the pattern of either Nppa or Nppb. These results show that, in chicken, the Nppa gene has been lost from the natriuretic peptide precursor gene cluster, whereas the CNP‐3 gene has been retained. Developmental Dynamics 233:1076–1082, 2005.

Patterns of expression of the Follistatin and Follistatin-like1 genes during chicken heart development: a potential role in valvulogenesis and late heart muscle cell formation.

The regulation of concentration and function of growth factors is of crucial importance to proper embryonic development of the heart. The patterns of expression of three extracellular modulators of the transforming growth factor‐β superfamily of growth factors, Follistatin, Follistatin‐like1, and Follistatin‐like3, are described with respect to heart development. Follistatin is highly localized in the endocardium covering the developing cardiac valves. Follistatin‐like1 is localized in the mesenchymal filling of the pharyngeal arches and broadly expressed in cells directly bordering myocardium. Follistatin‐like3 is not expressed in the heart. Taken together, these observations are suggestive for a role for Follistatin in cardiac valvulogenesis and a role for Follistatin‐like1 in controlling late heart muscle cell formation. Anat Rec, 2007.