3-D observation of N-cadherin expression during cardiac myofibrillogenesis of the chick embryo using a confocal laser scanning microscope.

It is not yet understood whether cell adhesion molecules play an active role in early cardiac morphogenesis or not. We present here the spatial and temporal expressions of N-cadherin and its relationships to actin filaments during looping (7- to 13-somite stages) of the chick embryonic heart tube observed by means of a confocal laser scanning microscope. Serial optical tomograms were obtained from the whole-mounted heart tubes stained with antibody to N-cadherin (fluorescein-conjugated) and phalloidin (rhodamine-conjugated). Three patterns of N-cadherin expression were observed during looping; a belt-like pattern, speckled pattern, and clumped pattern, corresponding to adhesion belt, nonjunctional cell contact and early intercalated disks, respectively. At the 7-somite stage, myocytes expressed N-cadherin as adhesion belt and nonjunctional cell contact. At the 8- to 10-somite stages, the clumped pattern of N-cadherin was detected before striated myofibrils appeared. Myofibrils began to develop across the clumps to form transcellular networks in the outer layer, and to form circumferential alignments in the inner layer. These results suggest that N-cadherin is responsible for the connection of myofibrils between the neighboring myocytes, and the alignment of the two layers in the developing heart tube.