Figure 1

Primary cilia are present in developmentally-important regions of the embryonic heart. (A, D) Transverse semithin sections of E12.5 mouse wild type (+/+) embryos showing the areas examined for ciliary ultrastructure in the atrioventricular endocardial cushions (A, black box) and the conotruncal endocardial cushions of the truncus arteriosus (D, black box). Dorsal is to the top. (B, C, E, F) Transmission electron microscopy of primary cilia born by mesenchymal (B, C ,F) or endocardial (E) cells of the cushions. Individual cilia are cut transversely (C) or longitudinally (B, E, F). Note the ‘9 + 0’ morphology characteristic of primary cilia (C) and the absence of a central microtubule doublet (B, C, E, F). (B) Black arrow, daughter basal body adjacent to a primary cilium. (B, E, F) Arrowhead, basal body of a primary cilium. (C) Black arrowhead, ciliary axoneme. Scale bars: (A, D) 300 μm, (B, E) 500 nm, (C, F) 200 nm. E12.5, embryonic day 12.5.