Expression of Tenascin in Fetal and Adult Salivary Glands Compared with the Expression of Type IV Collagen and Laminin-Histomorphological Roles.

Abstract

To elucidate the role of extracellular matrix and basement membrane associated proteins at the ectodermal-ectomesenchymal interface of developing salivary glands, human fetal submandibular glands (n=100), gestational age varying from 10 to 40 weeks, were evaluated for expression of tenascin, type IV collagen and laminin by using immunohistochemical methods and the results were compared with their expression in adult glands (n=20). Immunoreactive tenascin was present in the epithelial-mesenchymal interface of developing salivary ducts beginning from 10 weeks of gestational age during the early developing stages. In the late developmental stages, the intensity of immunoreaction was reduced around the proximal striated ducts and no immunoreaction was seen around the intercalated duct and acinar cells. Adult submandibular glands had immunoreactive tenascin confined to the periductal connective tissue of distal segment of striated and excretory ducts. Type IV collagen and laminin were observed in the basement membrane of salivary ducts and acini beginning from 16-18 weeks, and the intensity of reaction was more prominent during intermediate developing stages (19-32 weeks). The intensity of reaction was, however, less prominent in late developmental stages (33-40 weeks) which was similar to that in the adult glands. The present study suggests that tenascin forms an epithelial-ectomesenchymal interface before the organization of collagen IV and laminin in the basement membrane of salivary ducts and acini in developing human submandibular glands. The accumulation of the basement membrane proteins, however, are associated with stages of more active cytodifferentiation and morphodifferentiation of the glands.