Abstract
Background and Objectives: The dental pulp stem cells are highly proliferative and can differentiate into various cell types, including endothelial cells. We aimed to evaluate the ultrastructural characteristics of the human dental pulp cells of the permanent frontal teeth. Materials and Methods: Human adult bioptic dental pulp was collected from n = 10 healthy frontal teeth of five adult patients, prior to prosthetic treatments for aesthetic purposes. Tissues were examined under transmission electron microscopy. Results: We identified cells with a peculiar trait: giant nucleoli resembling intranuclear endoplasmic reticulum, which mimicked extrusion towards the cytoplasm. These were either partly embedded within the nuclei, the case in which their adnuclear side was coated by marginal heterochromatin and the abnuclear side was coated by a thin rim of ribosomes, or were apparently isolated from the nuclei, while still being covered by ribosomes. Conclusions: Similar electron microscopy features were previously reported in the human endometrium, as nucleolar channel system; or R-Rings induced by Nopp140. To our knowledge, this is the first report of extruded nucleolar structure in the dental pulp. Moreover, the aspect of giant extruded nucleoli was not previously reported in any human cell type, although similar evidence was gathered in other species as well as in plants.
Highlights
The dental pulp (DP), entrapped within the “sealed niche” of the pulp chamber, is interesting in regenerative medicine due to its accessibility and differentiation potential [1,2]
Mature nucleoli with homogenous morphologies were identified in spindle-shaped cells (Figure 1). They were most likely linked to the nucleolar organizer regions (NORs) of those nuclei, either central or polar
Those nucleoli were of comparable sizes and were partly embedded in the nucleus and partly extruded in the cytoplasm. They consisted of fibrillar centres, dense fibrillar components, and the granular component; on the adnuclear side, they were coated by heterochromatin, while on the abnuclear side they were coated by a thin rim ofribosomes, in direct contact with the intermediate filaments from the cytoplasm
Summary
The dental pulp (DP), entrapped within the “sealed niche” of the pulp chamber, is interesting in regenerative medicine due to its accessibility and differentiation potential [1,2]. There are several zones in the DP, each with its own cellular repertoire and specific role. The DP outer odontoblast layer ensures the production of dentin matrix and its subsequent calcification [3]. The cell-free zone of Weil is followed by a cell-rich zone 4.0/). The core harbours various connective cell populations, including DP stem cells—a cell population derived from neural ectomesenchyme, with a high proliferative profile and immunosuppressive activity [4,5]. Besides having a multilineage potential [6], dental pulp cells may release, under hypoxic stress, proangiogenic factors [7]
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