Ultrastructure of DNA-synthesizing and mitotically dividing myocytes in sinoatrial node of mouse embryonal heart.
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.
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*
D004247:DNA