Expression of HNK1 epitope by the cardiomyocytes of the early embryonic chick: In situ and in vitro studies

Abstract

Monoclonal antibody HNK1 reacts with a carbohydrate epitope in cell surface glycoproteins and glycolipids. During development, in various species the HNK1 epitopes are expressed in migrating neural crest cells and in the developing conduction cardiomyocytes. The conduction system is generally thought to be developed from cardiomyocytes, but some investigators have hypothesized that it is derived from the neural crest because conduction myocytes express neural antigens, including HNK1. Using immunohistochemistry, we examined the spatiotemporal expression of HNK1 in early chick cardiogenesis (stages 4 to 18) and whether cultured precardiac mesoderm does or does not express HNK1 as well as sarcomeric myosin (MF20). HNK1 was first expressed in the premyocardium at stage 8. At stage 10, HNK1-positive cardiomyocytes were scattered along the straight heart tube. By stage 18, HNK1-positive cardiomyocytes had become restricted to the atrium and sinus venosus. Atrioventricular cushion mesenchyme also expressed an HNK1 epitope. Immunostaining of HNK1 and MF20 in cultured precardiac mesoderm showed that there are at least three types of cells: 1) cardiomyocytes without HNK1 expression, 2) cells possessing both HNK1-and MF20-immunoreactivity, and 3) mesenchymal cells with HNK1. Immunogold electron microscopy showed that cardiomyocytes containing sparsely distributed myofibrils associated with the Z-band react with anti-HNK1 antibody. Our observations showed a direct evidence for the first time that the precardiac mesoderm generates HNK1-positive cardiomyocytes with morphological features similar to those of conduction cardiomyocytes.

HNK‐1 in Morphological Study of Development of the Cardiac Conduction System in Selected Groups of Sauropsida

“…Most of these studies used also additional markers to confirm specificity of expression, thus validating this antibody as a (temporal) marker of the CCS. Indeed, in vitro study on cultured precardiac mesoderm cells (Nakajima et al, ) showed that there are at least three cell types, that is, mesenchymal cells with HNK‐1 positivity, and positive and negative cardiomyocytes. However, the HNK‐1 is not, unlike, for example, some ion channels or gap junction proteins, a functional marker—and indeed is absent from the conduction system in the mouse.…”

“…The HNK‐1 monoclonal antibody is a marker for early migrating neural crest cells (NCC), but reacts also with structures, which are not derived from the neural crest (Gorza et al, ; Luider et al, ). Human natural killer (HNK)‐1, (the CD57 antigen or LEU7) is expressed as a carbohydrate epitope that contains a sulfoglucuronyl residue in several adhesion molecules of the nervous system (Nakajima et al, ). HNK‐1 epitope is also expressed in a subset of myocytes in the developing cardiac conduction system (CCS), making it a very useful, conserved marker for visualizing the CCS in mammals and birds (Nakagawa et al, ; Chuck and Watanabe, ).…”

Expression and Function of Ccbe1 in the Chick Early Cardiogenic Regions Are Required for Correct Heart Development

“…The extracellular matrix Tenascin-C, is also associated with cell motility [25] , [26] . Like Ccbe1, Tenascin-C is also expressed in the cardiogenic fields and disappear once the heart fields fuse [41] – [44] . However, no distinct phenothype was observed in tenascin-C-null mice [45] .…”

“…Interestingly, our results indicated that increased c Ccbe1 levels resulted in expansion of Hnk1-expressing domain in both CNC cells and heart tube region, while loss of c Ccbe1 decreased Hnk1 signal mostly in the heart tube region. Hnk1 plays a role in the migration of neural crest cells [25] , [26] , and is normally present in the cardiomyocyte precursor [41] – [44] .…”