Kazuhiro Takano1, Yuzuru Ito2, Shuichi Obata3, Tsutomu Oinuma4, Shinji Komazaki1, Hiroaki Nakamura1 and Makoto Asashima2,5,6,*
1Department of Anatomy, Faculty of Medicine, Saitama Medical University, Iruma, Saitama, 2International Cooperative Research Program (ICORP), Japan Science and Technology Agency (JST), Department of Life Science (Biology), Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, 3Division of Biology, College of Liberal Arts and Sciences, Kitasato University, Sagamihara, Kanagawa, 4Department of Anatomy Ultrastructural Cell Biology, Faculty of Medicine, University of Miyazaki, Kiyotake, Miyazaki, 5National Institute of Advanced Industrial Sciences and Technology (AIST), Tsukuba, Ibaraki and 6Department of Life Science (Biology), Graduate School of Arts and Sciences, The University of Tokyo, Meguro-ku, Tokyo, Japan.
ABSTRACT During vertebrate cardiac development, the heart tube formed by fusion of right and left presumptive cardiac mesoderms (PCMs) undergoes looping toward the right, resulting in an asymmetrical heart. Here, we examined the right and left PCMs with regard to heart-tube looping using right- and left-half newt embryos (Cynops pyrrhogaster ). In the half embryos, the rightward (normal) loop of the heart tube was formed from the left PCM, irrespective of the timing of its separation, while the leftward (reversed) loop of the heart tube was formed from the right PCM, separated by stage 18. In addition, the direction of the leftward loop was inverted to the rightward direction in right-half embryos bisected after stage 18. Incision or resection of the embryonic caudal region implicated interactions between the right and left sides of this region as crucial for inverting the direction of the heart-tube loop from leftward to rightward in the right-half embryos. In situ hybridization of CyNodal (Cynops nodal-related gene) suggested that the inversion of heart looping in the right-half embryos has no association with the CyNodal expression pattern. Based on these findings, we propose a mechanism for the rightward looping underlying normal amphibian cardiac development.Keywords:
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