Fig. 3. At stage 16 HNK-1-positive cells express a myocardial phenotype. Double
labeling by immunohistochemistry to show the relationship of HNK-1-positive
cells (green) to myocardial cells (red) in the cardiac outflow and inflow
tracts. The poles of the heart exhibit a gradient of HNK-1 and myosin protein
expression during looping, as seen in transverse sections of the outflow and
inflow poles of a stage 16 chick embryo double labeled for myosin. (A) The
distal outflow tract shows HNK-1-positive/MF20-negative cells in the
splanchnic mesoderm and HNK-1-negative/MF20-positive cells in the myocardium,
separated by myocardium that is positive for both HNK-1 and MF20 (yellow). (B)
The splanchnic mesoderm caudal to the attachment of the outflow tract with the
pharynx (arrow) is HNK-1 positive/MF20 negative. (C) The atrium displays a
gradient of overlapping protein expression, similar to that seen in the
outflow myocardium.
