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Fig. 2. Chamber and non-chamber myocardium in the forming heart. (A-D)
Illustrations of the developing mouse heart at E8.0 (A), E9.5 (B) and E11.5
(C), showing non-chamber (primary) myocardium (grey), ventricular chamber
myocardium (red), atrial chamber myocardium (blue), and the inflow and outflow
vessels (green). Note that chamber myocardium forms at the outer curvature of
the looping heart tube. Components in the forming heart (A-C) can be traced to
the adult heart (D). Primary myocardium forms the elements of the central
conduction system (see Box 3),
including the sinuatrial node (san), atrioventricular node (avn),
atrioventricular bundle (avb; bundle of His) and bundle branches (bb), as well
as insulating tissue of the atrioventricular junction (avj). Distal bundle
branches (dbb) and Purkinje fibres (pf) form within the interventricular
septum (IVS) and ventricular chambers, respectively. Yellow indicates the
derivatives of the AV canal, including insulating elements formed from
myocardium and valve leaflets formed from endocardial cushions. Modified from
Christoffels et al. (Christoffels et al.,
2004a), Copyright 2004 with permission from Elsevier. (E-J) In
situ hybridization analysis of sections of E8.75-E9.5 mouse embryos showing
mutually exclusive expression patterns of the heart chamber marker
Nppa (E-G) and Tbx2, a marker of non-chamber myocardium
(H-J, arrows). Reproduced with permission from Habets et al.
(Habets et al., 2002). a,
atrium; avc, atrioventricular canal; ev, embryonic ventricle; fg, foregut;
icv, inferior caval vein; ift, inflow tract; la, left atrium; lv, left
ventricle; oft, outflow tract; oftc, outflow tract cushion; pa, pharyngeal
arch; ra, right atrium; rv, right ventricle; scv, superior caval vein.
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