Developmental alterations of the heart outflow tract (OFT) cause conotruncal heart defects (CTHDs), which are often diagnosed in infants with congenital heart defects. During the early heart development, the OFT elongates by the addition of cardiomyocytes from the second lineage of heart-forming regions, which reside in the first and second pharyngeal arches (anterior heart field [AHF]) as well as in the splanchnic mesoderm of the pericardial coelom in the posterior pharyngeal arches (secondary heart field [SHF]) [1]. As the arterial pole moves in the anterior-to-posterior (cranial-to-caudal) direction, the AHF is first added to the OFT followed by the SHF. Therefore, abnormal development of certain parts of the AHF or SHF at certain stages may cause specific CTHDs.
Dye-marking experiments in chick embryos at the early looped-heart stage showed that the right and left AHFs migrate ipsilaterally to form the proximal OFT, whereas SHFs migrate rotationally to form the distal OFT beneath the semilunar valves [2]. The results indicated that each AHF/SHF migrates to generate distinct conotruncal regions.
Conotruncal heart defects produced by local administration of RA to the AHF or SHF at early looped-heart stage in chick embryonic hearts
RA addition | At stage 12a | At stage 14b |
---|---|---|
To AHF | TGA, DORV | PTA |
To SHF | PTA | PTA, DORV |
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