title: Epicardium-derived cells are important for correct development of the Purkinje fibers in the avian heart.
abstract: During embryonic development, the proepicardial organ (PEO) grows out over the heart surface to form the epicardium. Following epithelial-mesenchymal transformation, epicardium-derived cells (EPDCs) migrate into the heart and contribute to the developing coronary arteries, to the valves, and to the myocardium. The peripheral Purkinje fiber network develops from differentiating cardiomyocytes in the ventricular myocardium. Intrigued by the close spatial relationship between the final destinations of migrating EPDCs and Purkinje fiber differentiation in the avian heart, that is, surrounding the coronary arteries and at subendocardial sites, we investigated whether inhibition of epicardial outgrowth would disturb cardiomyocyte differentiation into Purkinje fibers. To this end, epicardial development was inhibited mechanically with a membrane, or genetically, by suppressing epicardial epithelial-to-mesenchymal transformation with antisense retroviral vectors affecting Ets transcription factor levels (n=4, HH39-41). In both epicardial inhibition models, we evaluated Purkinje fiber development by EAP-300 immunohistochemistry and found that restraints on EPDC development resulted in morphologically aberrant differentiation of Purkinje fibers. Purkinje fiber hypoplasia was observed both periarterially and at subendocardial positions. Furthermore, the cells were morphologically abnormal and not aligned in orderly Purkinje fibers. We conclude that EPDCs are instrumental in Purkinje fiber differentiation, and we hypothesize that they cooperate directly with endothelial and endocardial cells in the development of the peripheral conduction system.
authors.affiliation: Department of Anatomy and Embryology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Ismail
authors.initials: I
authors.lastname: Eralp
authors.forename: Heleen
authors.initials: H
authors.lastname: Lie-Venema
authors.forename: Noortje A M
authors.initials: NA
authors.lastname: Bax
authors.forename: Maurits C E F
authors.initials: MC
authors.lastname: Wijffels
authors.forename: Arnoud
authors.initials: A
authors.lastname: Van Der Laarse
authors.forename: Marco C
authors.initials: MC
authors.lastname: Deruiter
authors.forename: Ad J J C
authors.initials: AJ
authors.lastname: Bogers
authors.forename: Nynke M S
authors.initials: NM
authors.lastname: Van Den Akker
authors.forename: Robert G
authors.initials: RG
authors.lastname: Gourdie
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Schalij
authors.forename: Robert E
authors.initials: RE
authors.lastname: Poelmann
authors.forename: Adriana C
authors.initials: AC
authors.lastname: Gittenberger-De Groot
mesh_terms: D000818:Animals; D002450:Cell Communication; D002454:Cell Differentiation; D002465:Cell Movement; D048430:Cell Shape; D002642:Chick Embryo; D002645:Chickens; D003370:Coturnix; D016373:DNA, Antisense / Q000235:genetics / Q000378:metabolism; D006321:Heart / Q000196:embryology*; D010496:Pericardium / Q000196:embryology / Q000473:pathology*; D050784:Proto-Oncogene Protein c-ets-1 / Q000235:genetics / Q000378:metabolism; D050787:Proto-Oncogene Protein c-ets-2 / Q000235:genetics / Q000378:metabolism; D011690:Purkinje Fibers / Q000196:embryology / Q000473:pathology*; D013314:Stress, Mechanical
chemical_list: D016373:DNA, Antisense; D050784:Proto-Oncogene Protein c-ets-1; D050787:Proto-Oncogene Protein c-ets-2