Figure 2. Tcf21+ lineage cells contribute to ECF and Remak SC, but not myelinating SC, in the heart at P7.

(A) Representative images of Tcf21+ (Tcf21^MCM;R26^eGFP) ECF at P7 and P30. Immunofluorescence showed that Tcf21+GFP+ lineage traced cells are adjacent to intramural sympathetic nerves (TH+ areas) of the left ventricle (LV). P7 and P30 pictures were taken in the central area of the intramural region of the left ventricle. SB=15 μm. (B) Representative left ventricular immunofluorescence shows Tcf21GFP+ cells co-expressing P75NTR (Remak SC marker) but not PLP1 (non-myelinating SC marker) or GFAP (glial activation marker). Blue arrows point to PLP1+/GFP- cells in the top row and P75NTR+/GFP- cells in the bottom row. Pink arrows point to GFP+ cells. In the bottom row, white stars indicate GFP+/P75NTR+ cells. SB=15 μm. (C) Representative immunofluorescence images of Tcf21+/P75NTR+ ECF around epicardial sympathetic nerves (top row) and Tcf21+/P75NTR- ECF in the ventricular wall (bottom row). The ECF differentially express P75NTR with more expression in the epicardial, atria and atrio-ventricular space sympathetic nerves and minimal expression in the intra-mural sympathetic nerves. (N=5) SB=15 μm. (D) (Top row) Representative immunofluorescence images of Tcf21+ Remak SC in the left ventricle (LV) epicardium at P7. GFP+ lineage trace cells using a Tcf21^MCM;R26^eGFP co-express P75NTR (Remak SC/ECF marker) and Sox10 (glial marker), indicating that Tcf21 is not only expressed in ECF, but also in Remak SC at P7. Insets show Tcf21+GFP+ cells expressing Remak SC. (Bottom row) No co-expression of Sox10 and GFP was found in P30 Tcf21^MCM;R26^eGFP hearts. Yellow arrow points to Tcf21+/P75NTR-/Sox10- CF. Blue arrow points to Tcf21-/P75NTR+/Sox10+ Remak SC. (N=4). SB=15 μm. Quantifications are shown for (D’) % of Tcf21+ cells that co-express P75NTR (marker of SC and ECF) at P7 and (D”) % of Tcf21+/P75NTR+ relative to expression of Sox10 (glial marker) at P7 (N=5).