Characterization of the rat salivary-gland B1-immunoreactive proteins

Abstract

The B1-immunoreactive proteins (B1-IPs) are major secretory products of rat submandibular gland acinar-cell progenitors, and are also produced by neonatal and adult rat sublingual and parotid glands. In order to characterize the B1-IPs, we have previously isolated cDNA clones encoding rat parotid secretory protein (PSP; the predominant parotid B1-IP) and the related clone ZZ3, which is developmentally regulated in the neonatal submandibular gland. The remainder of the B1-IPs were uncharacterized. This report demonstrates that all of the B1-IPs are derived from the PSP and ZZ3 transcripts. Molecular cloning and Western-blot analyses using PSP- and ZZ3-specific antisera show that, of the B1-IPs, only PSP and neonatal submandibular gland protein A (SMGA) are products of the Psp gene. This finding corrects our previous assertion that SMGA is derived from ZZ3. Neonatal submandibular gland proteins B1 and B2, as well as apparent Mr 26000-28000 and Mr 18000-20000 forms in submandibular, sublingual and parotid glands, are derived from the gene encoding ZZ3 by differential N-glycosylation and by proteolytic cleavage. The apparent Mr 18000-20000 proteolytic products are significant in secretion product collected in vitro, but rare in gland homogenate and submandibular/sublingual saliva. The gene encoding ZZ3 has been named Smgb. Psp and Smgb are regulated similarly in the developing submandibular gland, but differently in the sublingual and parotid glands. The expression pattern of Psp is conserved between rat and mouse. However, no evidence for proteins derived from an Smgb-like gene was observed in neonatal mouse submandibular or sublingual glands.

Granule types and their morphological changes in terminal cluster and acinar cells in the late pre‐ and early postnatal rat sublingual gland

“…Pronase reacted with the electron-dense portion of Type I-III granules; however, immunohistochemical staining with anti-amylase antibody showed almost no positive reaction in these granules (data not shown). Ball et al (1993) and Mirels et al (1998) also demonstrated that highly electron-dense granules in secretory cells from the early postnatal mouse parotid gland, and in cells from the serous demilune of the mature rat sublingual gland contain protein B1. Furthermore, Wolff et al (2002) showed that by age 20 days in utero, mucous cells in the rat sublingual gland have granules labeled with antimucin, and serous cells have numerous granules containing CSP-1, SMGB, PSP, and SMGD.…”

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

“…It is well known that many salivary proteins undergo complex posttranslational modification, including glycosylation, and it is assumed that this has a major effect on their function . It is also note-worthy that rodent psp and smgb (Mirels et al 1998), as well as bovine bsp30a and b (Haigh et al 2008) have been shown to be N-glycosylated.…”

Submandibular Gland Adenocarcinoma of Intercalated Duct Origin in Smgb-Tag Mice

“…Immunoreactivity for parotid secretory protein (PSP), a salivary protein co-expressed with Smgb in the developing rat submandibular gland (Ball et al, 1988;Mirels et al, 1998), was used to identify proacinar and maturing acinar cells. Three days after birth, the mouse submandibular gland remained immature.…”

“…These mice contain a transgene in which Tag expression is targeted to intercalated ducts by regulatory sequences derived from the rat submandibular gland secretory protein b (Smgb) salivary protein gene (Gupta et al, 2000). Smgb is normally expressed in neonatal submandibular gland proacinar cells, and in a subset of intercalated duct cells of the adult gland (Ball et al, 1988;Mirels et al, 1998;Moreira et al, 1990). The Smgb-Tag transgene is expressed in these cells, but also in some neonatal submandibular gland secretory terminal tubule cells, and in the majority of intercalated duct cells.…”