A house with many rooms: how the heart got its chambers with foxn4
- Ethan David Cohen1 and
- Edward E. Morrisey1,2,3,4
- 1 Cardiovascular Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA;
- 2 Institute for Regenerative Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA;
- 3 Department of Medicine and Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
This extract was created in the absence of an abstract.
The vertebrate heart is initially formed from two lateral domains of cardiogenic mesoderm that fuse at the ventral midline to form a simple heart tube that is similar to the hearts or dorsal vessels of invertebrates. As development proceeds, this initial heart tube undergoes a series of morphogenetic rearrangements that subdivides the heart into the distinct chambers found in adult vertebrates. In this issue of Genes & Development, Chi et al. (2008) describe a novel transcriptional pathway required for separation of the outflow (ventricular) portion from the inflow (atrial) portion of the two-chambered zebrafish heart. This separation takes place at the atrioventricular (AV) canal, which forms the valves separating the ventricular and atrial compartments required for unidirectional blood flow, as well as the electrical conduction system required for proper cardiac rhythm. Chi et al. (2008) identify a member of the forkhead box (fox) family of transcription factors, foxn4, which works in concert with tbx5 to direct the development of the AV boundary by regulating the expression of tbx2b. This study sheds new light on how the AV canal myocardium became specialized during vertebrate evolution to perform its function as both the gatekeeper of blood flow and regulator of cardiac rhythm.
Development and function of the AV canal and foxn4
The basic design of the cardiovascular system changes dramatically during evolution to accommodate the increased blood flow and pressure found in vertebrates. In Drosophila, the peristaltic contraction of a simple myocardial tube promotes the circulation of hemolymph, the insect version of blood, within an open circulatory system. While this is sufficient for invertebrate species, which have small surface area-to-volume ratios and a relatively low demand for oxygenated blood, vertebrate species require more complex circulatory loops that provide directional flow of oxygenated blood from gas exchange organs such as lungs or gills to the rest of the …
