Skip to main content
. Author manuscript; available in PMC: 2014 Jan 1.
Published in final edited form as: Nat Biotechnol. 2012 Dec 16;31(1):54–62. doi: 10.1038/nbt.2465

Figure 3.

Figure 3

Morphological, epigenetic and functional features of Tbx18-transduced myocytes. Tbx18 leads to myofibrillar disorganization in NRVMs bearing resemblance to the unstructured myofibrillar network observed in the SAN in comparison to right atrium (RA). A. Neonatal rat SAN, demarcated by HCN4 expression (top middle), exhibits weaker and unstructured sarcomeric α-actinin (α-SA) expression (top panel). Bottom left: Zoomed-in image of the boxed area in top left. The pattern is faithfully recapitulated in Tbx18-NRVMs compared to GFP-NRVMs (bottom right and middle, respectively). Scale bar: 30μm. B. Comparison of cell area measurements (n=250 for each group) and cell membrane capacitance (n=16 for each group) indicate a 28% and 33% reduction (left and right, respectively) in Tbx18-NRVMs compared to control. C. Tri-methylation level on H3K27 indicates that Tbx18 increased inactivity of Cx43, Kir2.1, and α-SA promoters while relieving its repressive epigenetic pressure on HCN4 promoter normalized to control. Meanwhile, H3K4me3 levels indicate that ratio of active HCN4 promoter regions increased upon Tbx18 expression while the transcriptionally active promoter regions of Cx43, Kir2.1, and α-SA have decreased upon Tbx18 expression. (n=3 experiments. For each experiment, NRVMs from 6 wells of a 6-well plate were isolated for each group.) D. Focal expression of Tbx18 in the apex of guinea pig hearts in vivo created ectopic ventricular beats. Representative electrocardiographs (lead II) of GFP- or Tbx18-injected guinea pig (left and right, respectively, top panels). Ectopic ventricular pacemaker activity was observed in Tbx18-injected guinea pigs, but not in GFP-guinea pigs. Heart axis plots (bottom panels) suggest that the ectopic beats in Tbx18-guinea pig (right) originated near the site of gene injection (apex) and propagated towards the base. In contrast, the escape beats in control guinea pigs propagated toward the apex from the atrioventricular junction (left, n=5 for GFP-guinea pig and n=7 for Tbx18-guinea pig). E. The rate of ectopic ventricular beats in Tbx18-injected animals at day 3-5 after gene delivery is significantly higher than GFP-injected animals.