Differential expression of proliferative, cytoskeletal, and adhesive proteins during postnatal development of the hamster submandibular gland

Although the submandibular gland (SMG) plays important exocrine and endocri ne roles, little is known about the molecular details underlying its develo pment. Previously, we reported that in the postnatally developing hamster S MG, GPT the protein product of the first N-glycosylation gene, ALG7, was an in vivo marker for salivary cell proliferation. Here we investigated the p roliferative, cytoskeletal, and adhesive changes during SMG postnatal devel opment. The cellular localization and abundance of GPT, filamentous actin, and beta 1 integrin receptor were examined using confocal microscopy and im munoblotting. In neonatal glands, high GPT levels marked extensive cell pro liferation throughout the tissue. The apical regions of immature salivary c ells displayed intense actin staining, while most of the beta 1 integrin wa s diffusely distributed throughout the tissue. As development proceeded, di screte regions of the gland expressed attenuated levels of GPT, an increase d organization of actin to the cell cortex, and beta 1 integrin to the basa l lamina. In the adult SMG, differentiated salivary cells displayed low lev els of GPT and actin. While the abundance of beta 1 integrin remained uncha nged throughout development, in the adult, it was found exclusively in regi ons where cells contact the basal lamina. These data indicate that SMG deve lopment entails regionalized cell proliferation and polarization, and that these processes are temporally and spatially coordinated with the establish ment of stable cell-substratum interactions.