Elucidation of mechanisms controlling differentiation of salivary exocrine cells is required for development of cell-based therapeutics to treat patients after head/neck radiation or with autoimmune diseases. We are studying NFS/N-sld mice to elucidate factors in the differentiation of salivary mucous cells. In preliminary studies, we've identified a novel mouse gene (mSLG MUC) encoding the apomucin expressed in murine sublingual glands and have bioinformatic evidence for a syntenic human homologue. As these apomucins may represent gene products specific for mucous cells they are excellent focal points to study mucous cell differentiation and gene expression. We thus will: 1) Delineate the genomic organization of the mSLG MUC apomucin gene and its tissue and cell specific expression. We will also test the hypothesis that a putative human gene syntenic to mSLG MUC is expressed in human salivary mucous glands, and if so, delineate its genomic organization. We genetically mapped the sld mutation to a gene-poor critical region (=1.2 megabases on chromosome 15) that includes mSLG MUC. We will: 2) Determine the gene harboring the sld mutation and investigate the associated lesion responsible for the sld phenotype. The increase in mucous cell expression in sld-mice appears related to both glandular steady-state levels of apomucin transcripts and mucin glycoproteins. Our combined data indicate the sld phenotype is linked to expression of the apomucin. Interestingly, it has recently been determined that the major secretion product of neuroendocrine cells, chromogranin A, functions as a rate-limiting step in the biogenesis of secretory granules and regulated exocrine secretion. By analogy, we posit the sublingual apomucin functions to promote terminal differentiation of mucous cells. We will therefore: 3) Determine mechanism[sl by which steady-state levels of apomucin transcripts are regulated and also test the hypothesis that the mSLG MUC apomucin functions to promote the terminal differentiation of the mucous cell phenotype. From these combined studies, we characterize a novel gene, mSLG MUC, that likely represents the only known gene to be expressed selectively in salivary mucous cells. We also will evaluate the role of Mslg MUC in the terminal differentiation of mucous cells and determine its relationship to the sld mutation. Moreover, expression of a novel human gene expressing a salivary apomucin will be verified, and if expressed, would be the focus of future studies to determine mechanisms regulating its expression. ? ?
