Expression of class 3 semaphorins and neuropilin receptors in the developing mouse tooth

The semaphorins are a large family of secreted or cell-bound signals needed for the development of the nervous system. We compared mRNA expression of class 3 semaphorins (Sema3A. 3B, 3C and 3F) and their two receptors (Neumpi lin-1 and -2) in the embryonic mouse first molar tooth germ(E10-18) by radi oactive in situ hybridization. All genes showed distinct developmentally re gulated expression patterns during tooth organogenesis. interestingly. Sema 3A and 3C were first detected in the early dental epithelium and later both genes were present in the epithelial primary enamel knot, a putative signa ling center of the embryonic tooth regulating tooth morphogenesis. Prior to birth, Sema3A was also observed in tooth-specific cells. preodontoblasts, which later differentiate into odontoblasts secreting dentin, and in the me senchymal dental follicle cells surrounding the tooth germ. Sema3B appeared transiently in the dental mesenchyme in the bud and cap stage tooth while Sema3F was expressed in both epithelial and mesenchymal components of the t ooth. Of note. Npn-1 expression pattern was largely complementary to that o f Sema3A, and transcripts were restricted to the dental mesenchymal cells. Npn-l expression was first seen in the developing dental follicle. and late r transcripts also appeared in the dental papilla mesenchyme. In contrast, Npn-2 signal was seen in both epithelial and mesenchymal tissues such as in the primary enamel knot and preodontoblasts. (C) 2001 Elsevier Science Ire land Ltd. All rights reserved.