Nuclear characteristics of cardiac myocytes following the proliferative response to mincing of the myocardium in the adult newt, Notophthalmus viridescens

Abstract

Amphibian cardiac myocytes are predominantly mononucleated and have been demonstrated to respond to injury with DNA synthesis and mitosis. The nature of this response with regard to nuclear number and ploidy is unclear. In this study, the apex of the newt ventricle was minced and replaced, increasing the reactive area of the wound. At 45 days after mincing following multiple injections of tritiated thymidine (2.5 microCi/animal, 20 Ci/mM) 15 to 20 days after mincing, three ventricular zones were isolated and fixed: Zone 1, the minced area; Zone 2, extending approximately 500 micron proximally from the amputation plane; and Zone 3, the portion proximal to Zone 2. Myocytes separated in 50% KOH were examined for DNA synthesis by autoradiography and for nuclear number and DNA content using a scanning microdensitometer on Feulgen-Naphthol yellow S-stained cells. No labeled myocyte nuclei were found in control hearts and 98.3% of the myocytes were 2C. At 45 days, 46.78% of myocyte nuclei within Zone 1 were labeled, while 13% were non-diploid. In Zone 2, 9.25% were labeled with 4.8% non-diploid. In Zone 3, 1.1% were labeled, with 2.8% non-diploid. The newt ventricle's response to injury apparently may involve complete mitosis and cytokinesis, resulting in mononucleated diploid cells.

Heterogeneous proliferative potential in regenerative adult newt cardiomyocytes

“…Second, 19% of the cells go through more than one round of cell division in culture which may account for the 2.5 fold increase in the number of cardiomyocytes described in vivo, after injury (Bader and Oberpriller, 1979). Finally, the blocks to cell cycle progression described here are in agreement with the observations that 45 days after mincing the tip of the newt ventricle and grafting it back to the heart, 6% of the cells in the graft are binucleate and 7% are mononucleate with a polyploid nucleus (Oberpriller et al, 1989;Oberpriller et al, 1995). In control animals, only 1% of the cardiomyocytes have a polyploid nucleus and less than 1% are binucleate (Oberpriller et al, 1989).…”

“…The cells do not show any apparent distinction in terms of their differentiated state as they have very homogeneous morphology, they all express muscle markers and contract (our observations in culture) and they are all quiescent in the adult newt (Oberpriller et al, 1989). However, a clue to this variable behaviour is the fact that these cardiomyocyte clones show a similar pattern of cell division to the one previously described for embryonic cardiomyocytes (Burton et al, 1999).…”

“…We have shown that the majority of newt cardiomyocytes can enter into S phase and the differentiated state is compatible with complete cycles of division in 29% of newt cardiomyocytes. In each of these cases of plasticity, there is entry into the cell cycle and it is restricted to the zone adjacent to the wound (Brockes and Kumar, 2002;Oberpriller et al, 1989). Our results suggest that the same pathway drives newt cardiomyocytes and skeletal myotubes into S phase (Tanaka et al, 1997), since in both cell types this is enhanced by mammalian serum and is dependent on Rb inactivation, as evidenced by the strong inhibitory activity of p16 INK4 .…”

Primary cell culture and morphological characterization of ventricular myocytes from the adult newt, notophthalmus viridescens

“…Korecky et al (1979) have compared the percentages of binucleated myocytes in rat, rabbit, guinea pig, cat, dog, beef, and human hearts and described them as being 78%, 78%, 81%, 76%, 47%, 45%, and 10% binucleated, respectively. The relative absence of polyploid mononucleated, binucleated, or multinucleated myocytes in the adult newt heart (Oberpriller et al, 1988) suggests that the newt undergoes a pattern of nuclear change during growth and development which is different from the mammalian species that have been studied thus far.…”

Model Systems for Cardiovascular Regenerative Biology

“…d Poss et al (2002);Raya et al (2003). e Becker et al (1974);Oberpriller and Oberpriller (1974);Oberpriller et al (1988);Flink (2002). f Andersen et al (2005).…”