Secretory protein expression patterns during rat parotid gland development

Abstract

The rat parotid gland produces a number of well-characterized secretory proteins. Relatively little is known, however, about the onset of their synthesis and cellular localization during gland development. Secretory protein expression was studied in parotid glands of fetal and postnatal rats using light and electron microscopic immunocytochemistry and Northern blotting. Amylase, parotid secretory protein (PSP), common salivary protein-1 (CSP-1), and SMGB were first detected by immunofluorescence in parotid glands of 18 day fetuses. By 5 days after birth, light and electron microscopic immunolabeling localized all of these proteins to the secretory granules of developing acinar cells. Labeling of acinar cells for DNAse I, however, was not observed until 18 days after birth. Between 9 and 25 days, CSP-1 and SMGB reactivity of acinar cells declined, but increased in intercalated duct cells. After 25 days, CSP-1 and SMGB were found only in intercalated ducts, and amylase, PSP, and DNAse I were restricted to acinar cells. Levels of CSP-1 and SMGB mRNA were relatively constant through 21 postnatal days, but declined significantly after that. Amylase and PSP mRNA increased rapidly and continuously from five days after birth to the adult stage. In contrast, DNAse I mRNA was not detectable until 18 days after birth. The immunocytochemical and molecular analyses define three basic patterns of protein expression in the rat parotid gland: proteins whose synthesis is initiated early in development and is maintained in the acinar cells, such as amylase and PSP; proteins that are initially synthesized by immature acinar cells but are restricted to intercalated ducts in the adult gland, such as CSP-1 and SMGB; and proteins that are synthesized only by mature acinar cells and first appear during the third postnatal week, such as DNAse I. The parotid gland exhibits four distinct developmental stages: prenatal, from initiation of the gland rudiment until birth; neonatal, from 1 day up to about 9 days postnatal; transitional, from 9 days to 25 days of age; and adult, from 25 days on. Although differences exist in timing and in the specific proteins expressed, these developmental stages are similar to those seen in the rat submandibular gland. Additionally, the results support the suggestion that intercalated ducts may differentiate from the neonatal acini.

Developmental Morphology of the Palatine Glands in Rats: An Electron Microscope Study

“…Changes in diet (i.e., weaning from milk to solid food) and the hormonal environment may be involved. It is well established that significant changes in the synthesis of secretory proteins and the distribution of MECs in the rat parotid gland occur around the time of weaning (Redman et al, ; Denny et al, ; Sivakumar et al, ). The rodent submandibular gland undergoes substantial morphological and biochemical changes as a result of hormonal influences during sexual maturation (Gresik, ; Denny et al, ).…”

“…The procedures were conducted as described previously (Sivakumar et al, ; Wolff et al, ). Tissues were embedded in LR Gold resin (Electron Microscopy Sciences), then sections of 70–80 nm thickness were cut with a diamond knife and collected on Formvar‐coated 200 mesh nickel grids.…”

Expression and Localization of α-amylase in the Submandibular and Sublingual Glands of Mice

“…Serous acinar cells of the PG have not yet been formed at birth, but begin to develop from terminal clusters on the first postnatal day. They are serous in nature from the beginning and continue to develop until adulthood, with the increased expression of secretory products including α-amylase [23]. The molecular mechanisms underlying such diversity in salivary gland development from the common rudiment emerging in the embryonic oral epithelium remain to be elucidated [4].…”

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

“…Three are given here. (1) In parotid gland acinar cells, expression of Smgb mRNA is markedly down-regulated over 14-25 days post partum, when Psp transcription is elevated to high adult levels [9,30]. (2) In serous demilune cells of the SLG, Smgb transcription increases rapidly before birth, and postnatally SMGB becomes a major adult secretory protein.…”

“…Polyclonal antibodies raised against purified rat M1 protein were equally reactive against 23.5 kDa bands on Western blots of rat and mouse parotid secretions, suggesting that the rat protein is the homologue of mouse PSP [7]. In both mouse and rat, PSP appears during secretory granule formation in the first postnatal week, and increases by 21 days to the high adult level ( [8,9]; W.D. Ball, unpublished work).…”