Fig. 4. Atrial progenitors are present in the posterior SHF on right and left sides of Mlc3f-nlacZ-2E embryos at the 4-somite stage. (A-H) Left (L) (A-D) and right (R) (E-H) explants of the pSHF from Mlc3f-nlacZ-2E mouse embryos at the 4-somite stage, after 72 hours of culture. (A,E) Hoechst staining; (B,F) myosin heavy chain (MHC) immunofluorescence; (C,G) β-gal immunofluorescence. (D) Merge of B and C; (H) merge of F and G. Scale bar: 10 µm in H for A-H. (I) Quantitative analysis of β-gal and MHC double-positive cells, as a percentage of the total number of cells, in 30 explants from each side of the pSHF. White, percentage in left explants; black, percentage in right explants. (J) qRT-PCR analysis on ten pooled explants from left (l) and right (r) sides. lacZ (arrowheads) and Mlc2a transcript abundance is expressed as a percentage of that of Gapdh transcripts.