Psp and Smgb: a model for developmental and functional regulation in the rat major salivary glands

Abstract

This paper summarizes past work detailing the developmental expression, cell and organ localization and biochemical features of the proteins parotid secretory protein (PSP) and isoforms of submandibular gland protein B (SMGB), and describes the molecular characterization of the genes that encode them, Psp and Smgb. These genes appear to be related to the BPI (bactericidal/permeability-increasing protein)/LBP (lipopolysaccharide-binding protein)/PLUNC (palate, lung and nasal epithelial clone) gene family found in the oral and respiratory organs of humans, rodents and cattle. We have emphasized the diverse patterns of expression of these genes among the submandibular, sublingual and parotid salivary glands of the rat, and their potential usefulness in defining and identifying genomic regulatory mechanisms of salivary development. While Psp is expressed similarly in the mouse, the putative Smgb gene of the mouse seems not to be expressed, apparently due to the insertion, between exons 1 and 2, of a gene for a retroviral protein.

Characterisation and expression of SPLUNC2, the human orthologue of rodent parotid secretory protein

“…A second psp-related protein, submandibular gland protein B (smgb) was also identified in rats (Madsen & Horth 1985;Shaw & Schibler 1986) but is not present as a functional gene in mice (Ball et al 2003). We have recently shown that there are 4 psp-like proteins (called bsp30a-d) in the bovine genome that have arisen from a series of gene duplication events (Wheeler et al 2007).…”

“…It is now firmly established that SPLUNC2 is the human orthologue of rodent psp despite the very low level of sequence similarity that exists between the two proteins (Emes et al 2003;. psp was first identified as a significant component of rodent saliva and is known to appear during secretory granule formation in the major salivary glands in postnatal development and increases to a high adult level (reviewed in Ball et al 2003). A second psp related protein, submandibular gland protein B (smgb) was also identified in rats (Mirels & Ball 1992).…”

“…Expression of the two proteins in rats is discordant, since smgb is expressed at greater levels than psp in sublingual gland, whereas psp is a major parotid acinar cell product (Mirels & Ball 1992;Ball et al 2003). psp is produced by mouse salivary glands with similar temporal and cell specificity to rat psp, however, mouse smgb has been silenced through a viral integration event in the first intron (Ball et al 2003) and therefore mice are smgb deficient. Further psp-related proteins have been described in cow saliva and termed bovine salivary protein 30 kDa (bsp30) (Wheeler et al 2002).…”

Direct binding of parotid secretory protein to phosphatidylinositol phosphates.

“…It is a 23 kDa leucine rich protein [64,65]. It is present in immature acinar cells, seen as soon as the first postnatal week and increasing by 21 days to the high adult level [62].…”

“…Parotid Secretory Protein (PSP) is one of the most abundant proteins present in saliva secreted from rat parotid gland [61,62]. Rat PSP is the homologue of mouse PSP [63].…”