Mouse Serrate-1 and Notch genes differ in their response to signaling molecules during odontogenesis.

Serrate--like genes encode transmembrane ligands to Notch receptors and control cell fate decisions during development. This signaling system appears to function in most multicellular organisms since Notch receptors and Delta/Serrate ligands have been found in both invertebrates and vertebrates (Artavanis-Tsakonas et aI., 1995). Highly conserved homologue of the Drosophila Serrate have been recently identified in rat (Lindsell et aI., 1995) and in mouse. Jagged, the rat Serrate-I homologue, is believed to participate in Notch signaling as it seems to activate Notch in myoblasts in culture, as reflected by an inhibition of their differentiation (Lindsell et aI., 1995). Little is known about regulation of vertebrate Notch receptors and ligands. As a step towards addressing this issue, we have analysed the expression and regulation of the mouse Serrate-1 (Ser-1) gene during tooth development. Tooth develops as a result of sequential and reciprocal interactions between neural crest-derived mesenchyme and the oral ectoderm. Particular emphasis was given to tissue interactions, since it was previousry shown that such interactions and exposure to specific signaling molecules are critical in organizing the expression of Notch receptors during odontogenesis (Mitsiadis et aI., 1995),