Fig. 2

tbx1+ cells contribute to LPM-derived cardiac lineages. a–p Representative maximum intensity projections of whole-mount tbx1:EGFP-expressing embryos counterstained for anti-EGFP and anti-MHC (n = 3) (a–h) or anti-Isl1 (n = 11) (i–p) at 26 hpf; lateral views, anterior to the left. a–dtbx1 reporter expression can be detected in the MHC-positive linear heart tube and in the MHC-negative poles at the cardiac inflow and outflow tracts (arrowheads); e–h depicts a 2.25x magnification of the framed area in a–d. tbx1:EGFP also marks the pharyngeal arches (pa) and endothelial cells of the cranial vasculature (cv) (d). i–ptbx1 reporter-expressing cells at the IFT co-express the SHF marker Isl1 (asterisks n, o); m–p depicts a 3x magnification of the framed area in i–l. q Quantification of tbx1:EGFP/Isl1 double- compared to Isl1 single-positive cells at the IFT of the linear heart tube, n = 11 individual embryos analyzed, means ± s.d. r Lineage tracing of tbx1 and drl reporter-expressing cells, shown in representative embryos. tbx1:creERT2 (n = 11) or drl:creERT2 (n = 3) transgenics, respectively, were crossed to the ubiquitous hsp70l:Switch loxP tracer line, embryos were 4-OHT-induced at 90% epiboly, and heat-shocked at 3 dpf. s-a’ Live SPIM imaging of still hearts of representative lineage-traced and control embryos; maximum intensity projections of ventral views, anterior to the top, dashed outlines mark the heart with the bulbus arteriosus (BA), atrium (A), and ventricle (V). s–utbx1:creERT2 lineage tracing (tbx1 > EGFP) at late gastrulation labels myl7:DsRed2-expressing cardiomyocytes (arrowheads) in the ventricle and inflow tract of the atrium, and DAR-4M-stained cells (arrowhead) in the BA. v–xdrl:creERT2-mediated lineage tracing (drl > EGFP) at 90% epiboly marks all cardiomyocytes (arrowheads) in the ventricle and atrium, BA cells (arrowhead), and the endocardium (arrows). y-a’ tbx1:creERT2;hsp70l:Switch transgenics without 4-OHT treatment and heat-shocked at 3 dpf show no specific EGFP expression (asterisks mark the autofluorescent pigment cell). Scale bars 20 μm (e–h, m–p), 100 μm (a–d, i–l, s–a’)