A schematic model of two origins of blastemal progenitors in lower jaw regeneration.

<p>Two origins of blastemal progenitors (<i>foxi1</i>-positive neural crest cells and <i>isl1</i>-positive mesodermal progenitors) arise in the lower jaw blastema. They undergo mesenchymalization, chondrogenic differentiation and tissue respecifications toward skeletal, connective tissues and muscle regeneration through specific signaling pathways. The possible signaling communications are indicated. For instance, positional signaling mediated by local cues orchestrates blastema reformation; the activation <i>hoxa2b</i> and <i>hoxa11b</i> is induced/enhanced by the second arch signaling and blood signaling respectively.