Within the tooth, Rx-Cre activity is confined to the ameloblast layer.

<p><i>Rx-Cre^+/tg</i> mice were crossed to the <i>ROSA26^+/lacZ</i> Cre reporter line and Cre activity was assessed via X-gal staining. Rx-Cre exhibited broad activity throughout the anterior head in such tissues as the retina, tongue, skin, hair follicles, and teeth (A). Closer inspection of the incisors (B and C) and the molars (D and E) revealed that Cre activity was confined to the ameloblast layer (Am) and completely absent from the odontoblast layer (Od). The Cre activity in the molars was more mosaic than the incisors (arrows in E).