Fig. 1

Genetic labelling of zebrafish CMs using a UV-inducible Cre/lox recombination system. Double transgenic embryos (Tg(myl7:Cre-Ert2)^+/− × Tg(myl7:LnL-EGFP)^+/−) were treated at 2 dpf with (a) uncaged cyclofen (n = ∼100), (b) caged-cyclofen without UV exposure (n = ∼100) and (c,d) caged-cyclofen followed by UV exposure (n = ∼100). One fish tank per condition (approx. 40 larvae) was raised to adulthood. Cyclofen works as a tamoxifen analogue and induces recombination in CMs as observed by GFP expression at 4 dpf (a) and at adult stage (e,i). (b,f,j) Caged-cyclofen cannot induce recombination unless it is uncaged by UV exposure (c,d,g,h,k,l). Adult heart sections were processed for immunofluorescence with antibodies against MF20 and GFP. Nuclei were counterstained with DAPI. Scale bars: (a–d) 150 µm, (e–j) 250 µm, (k–l) 100 µm. Dashed lines in (a–d) define the ventricle perimeter.