title: Ultrastructure of DNA-synthesizing and mitotically dividing myocytes in sinoatrial node of mouse embryonal heart.
abstract: Unlike the cells of the working myocardium (WM), myocytes from the sinoatrial node (SAN) of the hearts of 16- to 18-day-old mouse embryos are small and 'pale'. They contain few poorly organized myofibrils and no specific granules. The frequency of myocytes labeled with 3H-thymidine or dividing mitotically is 3-4 times lower in the SAN compared to the WM. The ultrastructure of myofibrils and other cytoplasmic organelles in DNA-synthesizing myocytes of the SAN remains practically the same as in most of its muscle cells not labeled with 3H-thymidine. However in prometaphase Z-discs disappear and myofibrils break into free myofilament bundles. Intercalated discs and desmosomes persist in all mitotic phases. As a result of cytotomy, two daughter myocytes appear, while occasional acytokinetic mitoses give rise to binucleated cells of the SAN.
mesh_terms: D000818:Animals; D004247:DNA / Q000096:biosynthesis*; D005260:Female; D005318:Fetal Heart / Q000378:metabolism / Q000648:ultrastructure*; D007399:Interphase; D051379:Mice; D008809:Mice, Inbred C3H; D008854:Microscopy, Electron; D008938:Mitosis; D009210:Myofibrils / Q000648:ultrastructure; D011247:Pregnancy; D012849:Sinoatrial Node / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: D004247:DNA