title: An intrinsic timer that controls cell-cycle withdrawal in cultured cardiac myocytes.
abstract: Developing cardiac myocytes divide a limited number of times before they stop and terminally differentiate, but the mechanism that stops their division is unknown. To help study the stopping mechanism, we defined conditions under which embryonic rat cardiac myocytes cultured in serum-free medium proliferate and exit the cell cycle on a schedule that closely resembles that seen in vivo. The culture medium contains FGF-1 and FGF-2, which stimulate cell proliferation, and thyroid hormone, which seems to be necessary for stable cell-cycle exit. Time-lapse video recording shows that the cells within a clone tend to divide a similar number of times before they stop, whereas cells in different clones divide a variable number of times before they stop. Cells cultured at 33 degrees C divide more slowly but stop dividing at around the same time as cells cultured at 37 degrees C, having undergone fewer divisions. Together, these findings suggest that an intrinsic timer helps control when cardiac myocytes withdraw from the cell cycle and that the timer does not operate by simply counting cell divisions. We provide evidence that the cyclin-dependent kinase inhibitors p18 and p27 may be part of the timer and that thyroid hormone may help developing cardiac myocytes stably withdraw from the cell cycle.
authors.affiliation: Imperial College School of Medicine, National Heart and Lung Institute, London, United Kingdom.
authors.forename: P B
authors.initials: PB
authors.lastname: Burton
authors.forename: M C
authors.initials: MC
authors.lastname: Raff
authors.forename: P
authors.initials: P
authors.lastname: Kerr
authors.forename: M H
authors.initials: MH
authors.lastname: Yacoub
authors.forename: P J
authors.initials: PJ
authors.lastname: Barton
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics; D002452:Cell Count; D002453:Cell Cycle / Q000187:drug effects*; D018797:Cell Cycle Proteins; D002454:Cell Differentiation; D002455:Cell Division / Q000187:drug effects*; D002478:Cells, Cultured; D002999:Clone Cells / Q000378:metabolism; D050763:Cyclin-Dependent Kinase Inhibitor p18; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D006321:Heart / Q000196:embryology; D007150:Immunohistochemistry; D051379:Mice; D018345:Mice, Knockout; D018715:Microscopy, Video; D008869:Microtubule-Associated Proteins / Q000235:genetics; D009206:Myocardium / Q000378:metabolism*; D013696:Temperature; D014284:Triiodothyronine / Q000494:pharmacology; D025521:Tumor Suppressor Proteins
chemical_list: D002352:Carrier Proteins; C493961:Cdkn1b protein, mouse; C493972:Cdkn2c protein, mouse; D018797:Cell Cycle Proteins; D050763:Cyclin-Dependent Kinase Inhibitor p18; D004791:Enzyme Inhibitors; D008869:Microtubule-Associated Proteins; D025521:Tumor Suppressor Proteins; D014284:Triiodothyronine; D016222:Fibroblast Growth Factor 2; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases