title: 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.
authors.affiliation: Department of Anatomy, Saitama Medical School, 38 Morohongo, Moroyamacho, Iruma-gun, Saitama, 350-0495 Japan. yuji@saitama-med.ac.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Nakajima
authors.forename: K
authors.initials: K
authors.lastname: Yoshimura
authors.forename: M
authors.initials: M
authors.lastname: Nomura
authors.forename: H
authors.initials: H
authors.lastname: Nakamura
mesh_terms: D000818:Animals; D018959:CD57 Antigens / Q000096:biosynthesis*; D002478:Cells, Cultured; D002642:Chick Embryo; D018604:Epitope Mapping; D019084:Fluorescent Antibody Technique, Indirect; D006321:Heart / Q000196:embryology*; D006329:Heart Conduction System / Q000196:embryology / Q000378:metabolism / Q000648:ultrastructure; D066298:In Vitro Techniques; D008648:Mesoderm / Q000378:metabolism / Q000648:ultrastructure; D009206:Myocardium / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: D018959:CD57 Antigens