The processes of morphogenesis and differentiation of the hamster submandibular gland (SMG) are initiated during the last trimester of the prenatal period and continue well after birth. Although the morphogenic aspects of the early SMG development have been studied extensively, little is known about molecular controls involved in the progressive determination of SMG phenotype. In this application we propose to examine development of the hamster SMG in the context of the changing N- glycosylation potential of differentiating secretory cells. Since the N-glycosylation activity is determined by the level of expression of the first gene in the dolichol pathway of N-glycosylation, ALG7, we propose to use ALG7 as a molecular marker of developmental changes. The ALG7 gene is evolutionarily conserved and essential for growth. It encodes the dolichol-P-dependent N-acetylglucosamine-1-phosphate transferase, GPT, which catalyzes the synthesis of the first lipid-linked intermediate, Dol-PP-GIcNAc. By modulating the cellular activity of GPT cells control the level of the mature lipid-linked oligosaccharide precursor, Dol-PP-GIcNAc2Man8Glc3, for protein N-glycosylation. The yeast GPT is regulated by the 3 untranslated regions, 3 UTRs, of the multiple ALG7 transcripts. Recently we have cloned and sequenced the ALG7 cDNAs from the hamster SMG and shown that the salivary ALG7 gene is also transcribed into multiple mRNAs with different lengths of the 3 UTRs. RNAase protection studies confirmed that these multiple transcripts occur in vivo. We have shown previously that progression through the postnatal development of the hamster SMG is accompanied by a continual decrease in the expression of the ALG7 expression in the hamster SMG and they include, 1) characterization of the spatial and temporal relationship in ALG7 expression during development using the in situ hybridization and immunohistochemistry of whole tissue sections, 2) analysis of the ALG7- specific transcripts at different stages during postnatal development in differentiating acinar and ductal cell preparations, 3) correlation of transcriptional expression of ALG7 with the level of the enzymatic activity of GPT and the amount of the GPT protein product in differentiating secretory cells, 4) examination of the molecular mechanisms involved in development-dependent expression of ALG7 in differentiating acinar and ductal cells, 5) identification of the SMG- and differentiating-secretory cell-specific factors involved in ALG7 expression. Specific secretory cell types or classes of cellular differentiation will be identified with cell-restricted proteins as markers. These studies should provide an important advance in the understanding of molecular controls involved in the SMG development.
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