SPATIOTEMPORAL EXPRESSION OF THE HOMEOBOX GENE S-8 DURING MOUSE TOOTHDEVELOPMENT

The murine S-8 gene encodes a nuclear homeodomain containing transcrip tion factor that is expressed at sites of epithelial-mesenchymal inter actions, including those in cranofacial tissues. The spatiotemporal ex pression of S-8 mRNA was examined in tooth primordia by in situ hybrid ization. Ss transcripts were found in all stages of tooth development in 13- to 16.5-day-old mouse embryos (E13-E16.5), covering the early b ud stage up to the late bell stage. S-8 mRNA was found exclusively in the ectomesenchyme and its derivatives that originate from the neural crest: future pulp cells, odontoblast precursors and dental follicle c ells. Expression was highest at the late cap and early bud stages and declined at the mid-bell stage, in both first molar and incisor primor dia. In E13 jaw explants grown in organ culture for 48 h, S-8 mRNA was still present in first and second molar primordia after culture. At E 15.5, S-8 mRNA was also transiently present in the surrounding osteoge nic tissue. It is concluded that the distribution pattern of S-8 mRNA during tooth development indicates a role for the gene in defining the identity of dental papilla and follicle cells. It is speculated that the time-restricted expression of S-8 in tooth primordia involves esta blishing the definitive form of the tooth organ. (C) 1997 Elsevier Sci ence Ltd.