Role of SHH Signaling in Regulation of Prx Gene Expression

Prx1 and Prx2 are transcription factors co-expressed in the medial developing mandible. Prx1/Prx2 double knock-out mice exhibited a severely shortened mandible with only one or no mandibular incisors. The severe phenotype of the Prx double mutants implies that Prx genes are involved in the genetic pathway(s) that regulate morphogenesis of the medial region of the mandible. However, very little is known about the signaling pathways that regulate the restricted expression of Prx genes in the developing mandible. Objective: To determine the role of epithelially derived SHH on the expression of Prx genes in the medial mandibular mesenchyme. Methods: We examined the effects of medially placed beads soaked in different concentrations (1-4mg/ml) of SHH on the expression of Prx1 and Prx2 in the medial region of the developing mandible by using organ-cultured chicken mandibular mesenchyme. Moreover, the effects of the SHH antagonist cyclopamine at a concentration of 10μM on the expression of Prx genes were determined by using organ-cultured chicken mandibles with intact mandibular epithelium. Results: Beads containing high concentrations of SHH (2-4mg/ml) were able to maintain expression of Prx in the medial mandibular mesenchyme. Beads containing lower concentrations of SHH (1mg/ml) could also maintain Prx in the same region, but in a small proportion of the explants. Further observations show that treatment of mandibular processes with cyclopamine results in downregulation of Prx expression in the medial region. Conclusion: Our observations demonstrate that epithelially derived SHH regulates the expression of Prx1 and Prx2 in the underlying mesenchyme of the developing mandible. Supported by NIH grant DE08682.