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

Abstract

The developmental characteristics of serous cells appearing in the rat sublingual gland from the late prenatal to the early postnatal period were investigated in this study. Particular attention was paid to the morphological changes observed in the secretory granules at the histochemical and ultrastructural level. On prenatal day 18, granules with homogeneous high electron density (Type I granules), and mottled granules (Type II granules) with heterogeneous electron density appeared in the narrow luminar cytoplasm of cells constituting the terminal clusters. On prenatal day 19, these granules decreased in number and were replaced by bipartite granules (Type III granules) composed of a highly electron-dense core and a more electron-lucent rim. Pronase treatment almost completely digested the Type I and II granules and the electrondense core of the Type III granules, although some of the Type I and II granules in serous demilunes at a later stage were insufficiently digested. On prenatal day 19.5, homogeneous granules of low electron density (Type IV granules) appeared in the terminal clusters and acini, and increased in number daily, making up 92.8% of the total granules on postnatal day 28. The granule morphology on electron microscopy, Alcian blue, and periodic acid-Schiff staining strongly suggested that Type I and II granules were serous granules, Type IV granules were mucous granules, and Type III granules were transforming-type granules. None of the secretory cells showed chromatin condensation, which is a characteristic of apoptosis. These findings suggest that the developing rat sublingual gland from the late prenatal to early postnatal period has numerous serous granules in the terminal clusters and acini, and that the majority of granules are replaced by mucous granules through transforming-type granules. In addition, because apoptotic figures of secretory cells could not be detected, it appears that most of the serous cells in the developing rat sublingual gland might have changed to mucous cells. Anat Rec Part A 277A: 209 -215, 2004.

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

“…These results are also consistent with observations of postnatal rat palatine glands which suggested that the increased electron density of secretory granules in acinar cells at PN10 is due to the presence of phospholipid (Okamoto et al, 2008). Moreover, the appearance of a large number of cells with highly electron-dense granules agrees with reports on the developing sublingual glands (Redman and Ball, 1979;Kikuchi et al, 2004). Wolff et al (2002) suggested that the mucous and serous cells follow separate pathways of differentiation, and that the cells containing mixed granules are developing mucous cells.…”

“…Wolff et al () suggested that the mucous and serous cells follow separate pathways of differentiation, and that the cells containing mixed granules are developing mucous cells. On the other hand, Kikuchi et al () suggested that the granules in the secretory cells of the developing rat sublingual gland change from the serous to the mucous type during the process of granule production. In the submandibular glands, the proportion of mucous to serous substances in the acinar cells increased with the maturation during postnatal development (Yamashina & Mizuhira, ).…”

Capability of Tissue Stem Cells to Organize into Salivary Rudiments

“…These observations indicate that the dominant acinar cell type in developing parotid and sublingual glands is converted from the late prenatal to the early postnatal period. In neonate sublingual glands, acinar cells have numerous serous granules that are replaced by mucous granules according to the developmental stage [ 8 ]. The lack of acinar cell apoptosis in these glands indicates that most of the acinar cells transform, but they are not replaced by cells of another type.…”

Confocal laser scanning microscopic analysis of ectopic sublingual gland-like tissue inside the hamster submandibular gland

“…More recently, it was reported that the cells containing the mucous‐like granules or mixed granules are the precursors of the mucous acinar cells of the rat sublingual gland (Wolff et al, ). Kikuchi et al, () noticed that the majority of the granules replaced the mucous granules through transforming‐type granules in the developing rat sublingual gland. Therefore, they also suggested that most of the serous cells in the developing rat sublingual gland might have changed in to mucous cells.…”