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 endocrine roles, little is known about the molecular details underlying its development. Previously, we reported that in the postnatally developing hamster SMG, GPT, the protein product of the first N-glycosylation gene, ALG7, was an in vivo marker for salivary cell proliferation. Here we investigated the proliferative, cytoskeletal, and adhesive changes during SMG postnatal development. The cellular localization and abundance of GPT, filamentous actin, and β1 integrin receptor were examined using confocal microscopy and immunoblotting. In neonatal glands, high GPT levels marked extensive cell proliferation throughout the tissue. The apical regions of immature salivary cells displayed intense actin staining, while most of the β1 integrin was diffusely distributed throughout the tissue. As development proceeded, discrete regions of the gland expressed attenuated levels of GPT, an increased organization of actin to the cell cortex, and β1 integrin to the basal lamina. In the adult SMG, differentiated salivary cells displayed low levels of GPT and actin. While the abundance of β1 integrin remained unchanged throughout development, in the adult, it was found exclusively in regions where cells contact the basal lamina. These data indicate that SMG development entails regionalized cell proliferation and polarization, and that these processes are temporally and spatially coordinated with the establishment of stable cell-substratum interactions.