a, b Genome tracks show chromatin accessibility for cell clusters from snATACseq data at 14 dpf. Gray shading shows gill-specific accessible regions near the gata3 and ucmaa genes. Chromosome positions refer to the GRCz11 genome assembly. c–f gata3-P1:GFP drives expression in the posterior gill-forming arches at 3 dpf, the gill filament system at 14 dpf, and gill progenitors at the tips of primary filaments at 60 dpf, as well as some pillar cells (arrowhead) and gill chondrocytes (arrow) near the growing tips. sox10:dsRed labels cartilage and Draq5 nuclei. f ucmaa-P1:GFP drives highly restricted expression in sox10:dsRed+ gill chondrocytes (boxed region shown in merged and single channels to the right) but not hyaline cartilage (top left). g Model shows the initiation of gata3 expression in the posterior gill-forming arches through the gata3-P1 enhancer, maintenance of gata3 in gill progenitors at the tips of growing filaments, and expression of ucmaa in gill cartilage through the ucmaa-P1 enhancer. Both gata3-P1 and ucmaa-P1 contain predicted Gata3 binding sites. Scale bars, 100 μm (c, d, f), 20 μm (e).
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