title: Calcium handling precedes cardiac differentiation to initiate the first heartbeat.
abstract: The mammalian heartbeat is thought to begin just prior to the linear heart tube stage of development. How the initial contractions are established and the downstream consequences of the earliest contractile function on cardiac differentiation and morphogenesis have not been described. Using high-resolution live imaging of mouse embryos, we observed randomly distributed spontaneous asynchronous Ca2+-oscillations (SACOs) in the forming cardiac crescent (stage E7.75) prior to overt beating. Nascent contraction initiated at around E8.0 and was associated with sarcomeric assembly and rapid Ca2+transients, underpinned by sequential expression of the Na+-Ca2+exchanger (NCX1) and L-type Ca2+channel (LTCC). Pharmacological inhibition of NCX1 and LTCC revealed rapid development of Ca2+handling in the early heart and an essential early role for NCX1 in establishing SACOs through to the initiation of beating. NCX1 blockade impacted on CaMKII signalling to down-regulate cardiac gene expression, leading to impaired differentiation and failed crescent maturation.
authors.affiliation: Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.|The Hatter Cardiovascular Institute, University College London and Medical School, London, United Kingdom.
authors.forename: Richard Cv
authors.initials: RC
authors.lastname: Tyser
authors.affiliation: Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.
authors.forename: Antonio Ma
authors.initials: AM
authors.lastname: Miranda
authors.affiliation: Wellcome Trust, London, United Kingdom.
authors.forename: Chiann-Mun
authors.identifier: 0000-0002-7007-3649
authors.initials: CM
authors.lastname: Chen
authors.affiliation: The Hatter Cardiovascular Institute, University College London and Medical School, London, United Kingdom.
authors.forename: Sean M
authors.initials: SM
authors.lastname: Davidson
authors.affiliation: Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.
authors.forename: Shankar
authors.initials: S
authors.lastname: Srinivas
authors.affiliation: Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.
authors.forename: Paul R
authors.identifier: 0000-0002-9862-7332
authors.initials: PR
authors.lastname: Riley
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000096:biosynthesis; D015870:Gene Expression; D006321:Heart / Q000196:embryology*; D000069416:Intravital Microscopy; D051379:Mice; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000096:biosynthesis
chemical_list: D020746:Calcium Channels, L-Type; C499849:NCX1 protein, mouse; D019831:Sodium-Calcium Exchanger; D002118:Calcium
keywords: calcium; cardiac crescent; cardiomyocyte differentiation; contraction; development; developmental biology; heart; mouse; stem cells