The Shh signalling pathway in early tooth development

The Sonic Hedgehog (Shh) signalling pathway has been proposed to play an im portant role in mammalian tooth development. We describe the spatial and te mporal expression of genes in this pathway during early tooth development a nd interpret these patterns in terms of the likely roles of Shh signalling. We show that the two putative receptors of the Shh ligand, Ptc and Ptch-2, localise in different cells, suggesting Shh may function in different ways as an epithelial and mesenchymal signal. Shh signalling has previously bee n shown, in other organs, to stimulate cell proliferation. In this paper we analyse the Fgf signalling pathway in Gli-2 mutants and propose a mechanis m as to how Gli-2 may regulate cell proliferation in tooth development.