Fig. 4

Ameloblast morphology is compromised in the Satb1^−/− mouse incisors. a H&E staining of the sagittal sections of the P13 wt mouse incisor shows well-developed PABs adjacent to the mineralizing dentin (in pink); SABs and MABs situate next to the enamel layer (in dark red). (a1) PABs, residing between the dentin matrix (d) and a layer of stratum intermedium (SI), start to elongate and polarize with the nuclei shifting to basal end (closer to SI). (a2) SABs further elongate and polarize to develop ample supranuclear space to accommodate the increased organelles. Tomes’ processes extending into the enamel layer are present at the apical border of SABs, as indicated by red triangles. (a3) H&E staining shows the reduced MAB situated next to mineralizing enamel matrix (e) of wt mouse. b Ameloblasts at all stages are shorter, and the enamel layer is thinner in the Satb1^−/− mouse incisor as compared to control. (b1) H&E staining shows the shortened PAB in the Satb1^−/− mouse incisor. (b2) SAB in the Satb1^−/− mouse incisor was shortened and lacked Tomes’ processes. (b3) Shortened maturation ameloblasts and a thin enamel layer were detected in the Satb1^−/− mouse incisor. Scale bar in (a3) applied to (a1) and (a2), and in (b3) applied to (b1) and (b2), 50 μM. The picket fence appearance Tomes’ processes at the apical surface of wt SABs (see c) were visualized by staining the F-actin filament within the cellular protrusion by red fluorescent probe phalloidin, as indicated by red triangles and outlined by the white dotted line (see d). Immunostaining with an anti-amelogenin antibody (in green) shows that Tomes’ processes extended and were embedded into the organic enamel matrix (e). At the apical surface of Satb1^−/− SABs (see e), no organized cellular protrusion could be found to extend into the adjacent Satb1^−/− enamel matrix (e, labeled in green). The interface between Satb1^−/− SAB and e was outlined by a white dotted line (see f). Scale bar in c and e, 50 μM; in panel d and f, 10 μM