Figure 1. Expression of Prx1 protein during molar and incisor tooth development in WT mice. (A color version of this Fig. is included in the APPENDIX.) (A) Western analysis of Prx1 expression in tissue lysates derived from the anterior and posterior halves of the mandible, containing incisor and molar primordia, respectively. The data illustrate temporal changes in absolute levels of the 2 Prx1 isoforms (Prx1a and Prx1b) and a change in their ratio. (B–D) Immunohistochemistry of Prx1 protein expression (green) in frontal sections during molar and incisor tooth development (the 2 Prx1 isoforms cannot be distinguished by this method). Tissues were counterstained with propidium iodide (red). (B) At E13.5, high levels of Prx1 protein expression are present in mesenchyme surrounding maxillary (M¹) and mandibular (M₁) molar tooth buds; Prx1 protein is also localized in condensed mesenchyme adjacent to Meckel’s cartilage (data not shown). There is no expression in oral or dental epithelium. (C) By E14.5, Prx1 expression is more refined and is strong in condensed mesenchyme surrounding the maxillary and mandibular molars. Prx1 expression is also highly localized in the mesenchyme of the developing oral vestibule. (D) At E15.5, there is reduced Prx1 protein expression in the dental papilla, but expression remains constant in mesenchymal tissues lateral to M¹ and M₁. (E) In a frontal section at E14.5, Prx1 protein is detected in the dental papilla of the developing maxillary incisor tooth germ (I¹). Key: oral cavity (oc), tongue (t).