Fig. 4

Lamb1a limits SHF addition to the venous pole. (A-B?) Maximum intensity projections of confocal image z-stacks in Tg(myl7:eGFP);Tg(myl7:DsRed) double-transgenic sibling (A-A?) and lamb1a?25 mutant embryos (B-B?) at 55 hpf. GFP+;DsRed?SHF cells are visible at the venous (green dotted line) and arterial (blue dotted line) poles of the heart. (C,C?) Higher magnification of the dashed-yellow-boxed area in A?. Double GFP+;DsRed+ cells represent ?older? cardiomyocytes (white arrow), whereas GFP+;DsRed? cells represent newly added SHF cells (blue arrowheads). (D,E) Quantification of double GFP+;DsRed+ cardiomyocytes (D) and GFP+;DsRed? SHF cells (E) in the atrium of siblings (n=17) and lamb1a?25 mutants (n=16) at 55 hpf reveals an increase in newly added SHF cells in lamb1a?25 mutants compared with siblings. Data are mean±s.d., analysed with the Kolmogorov?Smirnov test. (F) Quantification of GFP+;DsRed? myocardial volume in the distal arterial pole in sibling (n=18) and lamb1a?25 mutant embryos (n=14) at 55 hpf reveals an increase in SHF myocardium in lamb1a?25 mutants compared to controls. Data are median±interquartile range, analysed with Welch's t-test; *=P<0.05, ns=not significant in all graphs. Scale bars: 10 ?m in C; 50 ?m in A,B.