Early Mesodermal Cues Assign Avian Cardiac Pacemaker Fate Potential in a Tertiary Heart Field

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Science  10 May 2013:
Vol. 340, Issue 6133, pp. 744-748
DOI: 10.1126/science.1232877

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Setting the Pace

The heart beats rhythmically throughout life. Highly specialized cardiac pacemaker cells control the timing of this beating. Bressan et al. (p. 744, published online 21 March) identified the embryonic location of the pacemaker precursors in early avian development and traced the cells throughout their incorporation into the heart. The events that establish the pacemaker lineage occur prior to the initiation of heart formation, and are governed, at least in part, by a class of Wnt signaling molecules.


Cardiac pacemaker cells autonomously generate electrical impulses that initiate and maintain the rhythmic contraction of the heart. Although the majority of heart cells are thought to originate from the primary and secondary heart fields, we found that chick pacemaker cells arise from a discrete region of mesoderm outside of these fields. Shortly after gastrulation, canonical Wnts promote the recruitment of mesodermal cells within this region into the pacemaker lineage. These findings suggest that cardiac pacemaker cells are physically segregated and molecularly programmed in a tertiary heart field prior to the onset of cardiac morphogenesis.

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