Additional file 1.

Mitotic marker phospho Histone H3 appears decreased in Tie2Cre^+/-Srf^f/f endocardial endothelial cells compared to wild-type littermates. Single-plane confocal images (630×) of sections of E11.5 mouse embryonic ventricular tissue (A, B) immunostained for endocardial endothelial cells (PECAM-1; red), cardiomyocytes (MF-20; green), and proliferating cells (phospho Histone H3, PhH3; blue). (C) Quantitation of PhH3-positive nuclei in either endocardial endothelial cells or cardiomyocytes (total PhH3-positive cells immunolabelled by PECAM-1 or MF-20 over four visual fields). Tie2Cre^+/-Srf^f/f mutant embryos exhibited reduced PhH3 immunoreactivity in endocardial endothelial cells compared to wild-type embryos, indicating a decrease in proliferation (arrowheads; C, left graph). MF-20-positive cardiomyocytes in mutant tissue exhibit a mild decrease in PhH3 immunostaining (arrows; C, right graph), which is consistent with the apparent reduction in overall myocardial size. Decreased myocardial mass is likely a secondary effect of inadequate signalling from SRF-null endocardial endothelial cells rather than Cre-mediated direct excision of SRF in cardiomyocytes. Also, consistent with previous reports (Nelson et al., Circ. Res. 2004), presumed epicardium is negative for PECAM-1 staining in both wild-type and mutant embryos (asterisks). Scale bar: A, B = 30 μm.

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Holtz and Misra BMC Developmental Biology 2008 8:65   doi:10.1186/1471-213X-8-65