Iroquois Homeobox Protein 4 (IRX4)

Mouse and human IRX4 cDNAs encode deduced proteins of 515 and 519 amino acids, respectively, which share 83% sequence identity. In situ hybridization and Northern blot analysis in mice demonstrated that Irx4 transcripts are present in the developing central nervous system, skin, and vibrissae, but are predominantly expressed in the cardiac ventricles. In mice at embryonic day (E) 7.5, Irx4 transcripts are found in the chorion and at low levels in a discrete anterior domain of the cardiac primordia. During the formation of the linear heart tube and its subsequent looping, Irx4 expression is restricted to the ventricular segment. Throughout all subsequent stages in which the chambers of the heart become morphologically distinct and into adulthood, cardiac Irx4 expression is found exclusively in the ventricular myocardium.