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181 Epigenetics: Linking Genotype and Phenotype in Development and Evolution, ed. Benedikt Hallgrímsson and Brian K. Hall. Copyright  by The Regents of the University of California. All rights of reproduction in any form reserved. 11 epigenetic Interactions of the cardiac neural crest Martha Alonzo, Kathleen K. Smith, and Margaret l. Kirby Epigenetic interactions as envisioned by Waddington involved animal, tissue, or cell responses to environmental cues such as hormones , cell–cell interactions, and mechanical and electrical forces. These mechanisms shape the “landscape” a cell travels through to reach its final differentiated state. In the case of neural crest cells, which migrate from their origin in the dorsal neural tube to distant target sites, there is a signaling landscape in addition to a changing geographic landscape. The signaling landscape includes both received signals and emitted signals. To fully appreciate the epigenetic interactions of the cardiac neural crest, it is first important to understand the geographic landscape through which these cells migrate and the tissues that they either target or influence , or are influenced by, on their journey. This information allows us to understand the “historical landscape” that shapes their final disposition as well as the cells that they influence . In the case of the cardiac crest, the geographical landscape includes the caudal pharynx and the cardiac outflow tract. In the caudal pharynx, cardiac crest cells are necessary for repatterning the aortic arch arteries to the great arteries and for modulating signaling between the pharyngeal endoderm–ectoderm and cardiac outflow progenitors in the caudal pharynx. This modulation of signaling is essential for addition of myocardial cells from the ventral caudal pharynx to the outflow tract. Finally, cardiac conTenTs Cardiac Neural Crest Epigenetic Interactions of Cardiac Neural Crest Cells Cardiac Neural Crest as an Epigenetic Factor in Aortic Arch Artery Remodeling Cardiac Crest Cells Modulate FGF8 Signaling in the Pharynx to Regulate Arterial Pole Development Cardiac Neural Crest Cells as an Epigenetic Factor in Outflow Tract Septation References 182 organ development crest cells migrate into the outflow tract and orchestrate outflow tract septation. We will first discuss the migratory path of the cardiac crest and then the potential epigenetic interactions in more detail. cARDIAc neuRAl cResT Neural crest cells originate from the border between the neural and surface ectoderm along the rostrocaudal extent of vertebrate embryos. Generally, the crest originating cranial to somite 5 is called the “cranial neural crest,” while the crest originating caudal to somite 5 is known as the “trunk neural crest” (Le Lievre and Le Douarin 1975). The cranial crest is capable of generating ectomesenchyme in addition to the neural derivatives and melanocytes generated by all crest cells. The subpopulation of cranial neural crest cells that originates between the mid-otic placode and somite 3 contributes to pharyngeal and cardiac structural development and, because of its unique importance in cardiac development , has been called the “cardiac neural crest” (Kirby et al., 1983; Kirby and Stewart, 1983). In chick and mouse, the cardiac crest migrates as the most caudal of the three cranial streams of the neural crest that originate from the rhombencephalon (Figure 11.1). The postotic stream extends to somite 5, and the cardiac neural crest is found within this stream. Quailto -chick chimeras showed that the cardiac neural crest originated between the mid-otic placode and somite 3 and, thus, represents at least part of the post-otic stream. Some of the crest cells originating from the mid-otic placode to somite 3 migrate to the gut and elsewhere, so the term cardiac crest refers only to the cells that initially populate pharyngeal arches 3–6. Transplantation and focal cell–labeling studies in mouse showed that the cardiac crest in the mouse originates between the post-otic hindbrain and somite 4 (Chan et al., 2004). The neural tube opposite somite 2 is the largest source of cardiac crest cells. The three streams of the cranial crest are conserved across all vertebrates, and this caudal stream can be seen in animals as diverse as the lamprey (McCauley and Bronner-Fraser, 2003), Australian lungfish (Ericsson et al., 2008), Mexican axolotl (Ericsson et al., 2004), zebrafish (Eisen and Weston, 1993), mouse (Serbedzija et al., 1992), opossum (Vaglia and Smith, 2003), and chick (Kuratani and Kirby, 1992). It is not known whether the caudal stream in all vertebrates contains a cardiac crest as described in the chick and mouse, although the cardiac crest has been described in both zebrafish and frog embryos (Li et al., 2003; Martinsen et al., 2004...

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