Expression of hLAMP-1-Positive Particles During Early Heart Development in the Chick.

Heart development requires coordinated activity of various factors, the disturbance of which can lead to congenital heart defects. Heart lectin-associated matrix protein-1 (hLAMP-1) is a matrix protein expressed within Hensen's node at Hamburger-Hamilton (HH) stage 4, in the lateral mesoderm by HH stages 5-6 and enhanced within the left pre-cardiac field at HH stage 7. At HH stages 15-16, hLAMP-1 expression is observed in the atrioventricular canal and the outflow tract. Also, the role of hLAMP-1 in induction of mesenchyme formation in chick heart has been well documented. To further elucidate the role of this molecule in heart development, we examined its expression patterns during HH stages 8-14 in the chick. In this regard, we immunostained sections of the heart during HH stages 8-14 with antibodies specific to hLAMP-1. Our results showed prominent expression of hLAMP-1-positive particles in the extracellular matrix associated with the pre-cardiac mesoderm, the endoderm, ectoderm as well as neuroectoderm at HH stages 8-9. After formation of the linear heart tube at HH stage 10, the expression of hLAMP-1-stained particles disappears in those regions of original contact between the endoderm and heart forming fields due to rupture of the dorsal mesocardium while their expression becomes confined to the arterial and venous poles of the heart tube. This expression pattern is maintained until HH stage 14. This expression pattern suggests that hLAMP-1 may be involved in the formation of the endocardial tube.