Plk1 & Myocardial Regeneration Figure 7. Loss of cell cycle markers from the developing rat heart correlates with the decline in proliferative capacity of the cardiac myocyte. Hearts were excised from embryonic (E18), neonatal (P3 and P10), and adult Wistar rats, frozen in embedding media and sections were cut at 4 mm. Left hand panel (A, C and E) show bar chart summaries (n = 3, SEM, * p,0.05) while the right hand panel (B, D and F) show representative sections for each cell cycle marker at each age group. (B) Cardiac myocytes were identified by the cardiac myocyte-specific marker, tropomyosin (red), histone H3 phosphorylated at Ser10 (green), and nuclei were stained with DAPI (blue). (D) Cardiac myocytes were identified by the cardiac myocyte- specific marker, tropomyosin (red), histone H3 phosphorylated at Ser28 (green), and nuclei were stained with DAPI (blue). (F) Cardiac myocytes were stained with the cardiac myocyte specific marker, troponin I, Ki67 staining is red and DNA was stained with DAPI (blue). doi:10.1371/journal.pone.0006752.g007 PLoS ONE | www.plosone.org 10 August 2009 | Volume 4 | Issue 8 | e6752