Comparison of mitosis in binucleated and mononucleated newt cardiac myocytes

Abstract

Background: The cultured adult newt ventricular myocyte has been shown to undergo mitosis and cytokinesis in a fully differentiated state. Insight into its proliferation and cellular changes during the repair process involves obtaining a better understanding of the nuclear pattern (mononucle-ated, binucleated, or multinucleated) resulting from mitotic events. Mitosis is easily observable in cultured newt cardiac myocytes using phase-contrast microscopy. Methods: From days 8-19 in culture, the process of mitosis in mononucle-ated and binucleated newt ventricular myocytes was recorded and timed by using time-lapse video microscopy. Cultured cardiac myocytes were double-stained for myosin and F-actin by using fluorescein isothiocyanate (FITC)-labeled MF20 and rhodamine phalloidin. Results: Mitotic, mononucleated myocytes produced mononucleated daughter cells in 80% of the cases, whereas 20% were single, binucleated myocytes. In binucleated myocytes, only 32% underwent complete cytokinesis to produce two binucleated daughter cells, whereas 68% resulted in variably nucleated myocytes. Mononucleated and binucleated myocytes undergoing mitosis had similar time intervals for the period from nuclear breakdown (prometaphase) to the start of anaphase (108.7 minutes and 94.5 minutes, respectively), but the period between anaphase and midbody formation was significantly shorter in binucleated than in mononucleated myocytes (43.5 minutes and 69.3 minutes, respectively). The myofibrillae were not as well organized in binucleated myocytes as those observed in mononucleated myocytes. Conclusions: Mitosis in vitro appears to proceed more rapidly in binucle-ated newt cardiac myocytes, which have more poorly organized myofibrillae than mononucleated myocytes. Mitosis of cultured binucleated myocytes commonly results in variably nucleated daughter cells, whereas mononucle-ated myocytes produce predominantly mononucleated daughter cells. Anat.

Cardiomyocyte Proliferation: A Platform for Mammalian Cardiac Repair

“…36 The same has been observed in adult newt cardiomyocytes. 18,37 However, our study has demonstrated neither adult cardiomyocyte proliferation in vivo nor its relevance after myocardial injury.…”

Cardiac Myocyte Cell Cycle Control in Development, Disease, and Regeneration

“…However, while restricted cell cycle reentry may occur in the injured human versus mouse hearts [1-4% (13) human vs. 0.0014% mouse (210) cardiac myocytes], the ultimate fate of these myocytes and whether species-specific differences really exist with respect to proliferative capacity remain unresolved. In contrast, in species such as newt where consensus exists on the capacity for myocardial regeneration, it has been demonstrated that mononucleated myocytes were more likely to successfully undergo cytokinesis than binucleated myocytes (150). When binucleated newt myocytes enter the cell cycle, it resulted in variably nucleated myocytes in the majority of cases as opposed to cytokinesis.…”

Building and re-building the heart by cardiomyocyte proliferation

“…By contrast, this degree of binucleation is not seen in zebrafish; ∼95% of cardiomyocytes in the adult zebrafish heart are mononucleated (Wills et al, 2008). Findings in newts suggest that mononucleated cardiomyocytes are more likely to undergo cytokinesis than their binucleated counterparts (Matz et al, 1998). This tendency appears to hold true in mammals: in their examination of the effect of Nrg1/ErbB4 signaling on adult mouse cardiomyocytes, Bersell et al noted that mononuclear cells were more likely to undergo both karyokinesis and cytokinesis after Nrg1 treatment in vitro and in vivo (Bersell et al, 2009).…”