May play a role in development of the heart. Cranial mesenchyme, limb buds, axial mesoderm, and branchial arches and their derivatives. Also found in the heart especially in the ventricular septum and ductus arteriosus. Expressed at high levels in 8.5 day embryos in the mandibular arch while a lower expression is seen in the extraembryonic mesoderm. Expression is abundant at days 8.5 and 9.5 in the developing visceral arches and the splanchnic mesoderm surrounding the gut. Present in the myocardium from days 8.5-12.5. At day 14.5 present in valves and extensively in the ventricular septum. Belongs to the paired homeobox family.