Fig. 3. Expression of Sema3a in 1- (PN1) and 4-day postnatal (PN4) first (I), second (II) and third (III) lower molar tooth germs. Bright-(A1,C1) and dark-field (A2,C2) images of sagittal sections as well as (B) three-dimensional reconstruction of Sema3a (in red) expression in PN1 first molar tooth germ shown from below. Sema3a is absent from the sites of the secondary anterior (mesial) and posterior (distal) secondary apical foramina. The inner dental epithelium (gray) is 30% transparent to better visualize Sema3a expression in the dental papilla around the secondary apical foramina. Three-dimensional reconstruction was rendered using a perspective camera view. Scale bars: 200 µm. White arrows indicate Sema3a expression in dark-field images. a, developing alveolar bone; cl, cervical loop; d, dentin; e, enamel; dp, dental papilla; ode, outer dental epithelium; p, developing pulp floor; sr, stellate reticulum.