Hedgehog Signaling in Palatal and Facial Development

Abstract

The Hedgehog (HH) signaling pathway has shown to be crucial in modulating mammalian skeletal and craniofacial development, mutations in which can lead to craniofacial malformations such as cleft lip/palate. With three known homologues, including Desert Hedgehog (DHH), Sonic Hedgehog (SHH), and Indian Hedgehog (IHH), only the latter two are expressed in the craniofacial complex. The focus of this review pertains to the role of SHH and IHH signaling in palatal and facial bone development, and the underlying differences between the two. While expression of both SHH and IHH is required for calvarial ossification and craniofacial development, they differ in where they are expressed and how they elicit their effects. SHH is not expressed in the facial mesenchyme, but rather in the frontonasal and maxillary cranial suture mesenchyme. IHH expression by contrast occurs on developing palatine bone and in most studies pertains to endochondral ossification, playing a key role in inducing cell proliferation and differentiation.