Signaling centers coordinate tooth morphogenesis. The stages of mouse incisor (top) and molar (bottom) development are depicted in sagittal and frontal views, respectively. Tooth development begins with the appearance of a localized thickening of the oral epithelium (blue) to form the dental placode, which continues to thicken and then invaginates into the underlying dental mesenchyme (yellow), forming a tooth bud. The subsequent folding of the tooth bud into a cap-shaped enamel organ and the continued condensation of surrounding mesenchyme form the tooth germ. Ahtiainen et al. (2016) identified the cellular mechanisms by which the early signaling center of the incisor (IK; purple) formed, and they established the relationship between the IK and the better-studied EK (red) of the incisor. The early signaling center has not yet been examined in detail in the molar, which, unlike the incisor, has both primary (pEK) and secondary EKs (sEK).