The vertebrate body plan is far from symmetrical, both in terms of left-right (LR) organ asymmetries and LR positioning of the heart and viscera. These asymmetries originate early in development when the LR axis of the embryo is established. Errors in this process cause laterality disorders, many of which include congenital heart defects. On p. 1399, Ramsdell and co-workers investigate how LR positional information is translated into anatomical asymmetry by determining the left or right origin of the myocytes in the developing Xenopus heart. They fluorescently labelled left and right blastomeres of four-cell embryos and tracked where they went in the hearts of normal embryos and embryos in which LR patterning had been disrupted. Their detailed analysis reveals that whenever the LR body axis is compromised, the LR cell lineage composition of the heart is abnormal. Such defects are almost always associated with congenital heart defects, which indicates that the proper allocation of LR cell lineages to the heart is central to normal heart morphogenesis.
- © 2006.