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Fig. 3 Cardiac contraction promotes endocardial id2b expression through primary cilia. (A) Representative confocal z-stack (maximal intensity projection) of id2b:eGFP embryos under different conditions: control, tricaine-treated, blebbistatin-treated, and tnnt2a morpholino-injected. Images were captured using the same magnification. (B) Quantification of mean fluorescence intensity (MFI) of id2b:eGFP in the working myocardium (atrium and ventricle, A+V) and atrioventricular canal (AVC) in (A). Data normalized to the MFI of control hearts. n=(11, 15) (ctrl versus tricaine); n=(5, 6) (ctrl versus blebbistatin); n=(10,11) (ctrl versus tnnt2a MO). (C) Representative confocal z-stack (maximal intensity projection) of control and ift88 morpholino-injected id2b:eGFP embryos. (D) Normalized MFI of id2b:eGFP in the working myocardium (A+V) and AVC in (C). n=(17, 9). (E) Whole-mount in situ hybridization showing id2b expression in control, klf2a-/-, and klf2b-/- embryos at 48 hr post-fertilization (hpf) and 72 hpf. Numbers at the bottom of each panel indicate the ratio of representative staining. Data are presented as mean ± s.e.m. Unpaired two-tailed Student’s t-tests were used to determine statistical significance. **p<0.01, ***p<0.001, ****p<0.0001. Scale bars, 50 μm.