Fig. 9.

Mycn recapitulates HH signaling-mediated adult cardiomyocyte proliferation. a qPCR analysis of Mycn transcripts using RNA obtained from isolated cardiomyocytes at P2, P7, and P60 mouse hearts (n = 3). b qPCR analysis of Mycn transcripts using RNA obtained from adult uninjured and injured heart tissue at 7 days post-MI. c qPCR analysis of Mycn transcripts using RNA obtained from control and SmoM2-expressing heart tissue following 7 days post-MI. d, e Immunohistochemical images (d) and quantification (e) of α-Actinin⁺-pH3⁺ isolated adult cardiomyocytes following transfection with Gfp and Mycn mRNAs at 48 h. Quantitative analysis represents the counting of ten different fields at 10× from three replicates (n = 450 cardiomyocytes for each condition). f–h Quantitative analysis of the number of mono-, bi-, and multi-nucleated cardiomyocytes from Gfp and Mycn mRNAs transfected adult cardiomyocytes. Quantitative analysis represents the counting from multiple fields at 10× magnification from three replicates. i Schematic model depicting the Shh-Gli1-Mycn regulatory network and cardiomyocyte proliferation. Gli1 transcription factor is induced as a downstream effector of HH signaling upon the binding of the Shh morphogen to its membrane receptor. Gli1 and Gli3 function in an antagonistic fashion as Gli1 promotes proliferation whereas Gli3 acts to repress the proliferative program and induces maturation. Activated Gli1 transactivates its downstream target, Mycn, to regulate the proliferative response in cardiomyocytes. Data are presented as mean ± SEM (*p < 0.05; **p < 0.01). Scale bars = 200 μm. Statistical tests were done using two-tailed unpaired Student’s t-test