This paper systematically elaborates on the key points of diagnosis and differential diagnosis of salivary gland tumors characterized by a substantial amount of extracellular mucus as a main or prominent feature, and clarifies the core differential features. The term "mucus-rich" specifically denotes that mucus is a major component of the tumor, rather than a focal or minor one. This phenomenon is associated with distinct histogenetic mechanisms: it may result from specific genetic mutations (e.g., AKT1 E17K in mucinous adenocarcinoma) that drive ductal epithelial differentiation into mucus-secreting cells, or from myoepithelial cells secreting glycosaminoglycans that form a myxoid stroma. Salivary gland tumors with abundant extracellular mucus include mucinous cystadenoma, sialadenoma papilliferum-like intraductal papillary tumors, mucinous myoepithelioma, pleomorphic adenoma with mucin-rich stroma, mucinous adenocarcinoma, low-grade mucoepidermoid carcinoma, mucin-rich salivary duct carcinoma and intestinal-type adenocarcinoma. The diagnosis of these tumors is complicated by the dual nature of extracellular mucus: while it is a defining feature of some entities, it can also obscure key diagnostic architectural features in others, leading to histological overlap and inconspicuous diagnostic areas. Given the frequent histological morphological overlap among these tumors, immunohistochemical findings and molecular characteristics have emerged as crucial differential diagnostic criteria. Core differential diagnostic points include the following: histologically, there must be meticulous identification of typical structures obscured by mucin (such as squamoid cells in mucoepidermoid carcinoma and apocrine features in salivary duct carcinoma); in immunohistochemical staining, CK20 is useful for distinguishing intestinal-type adenocarcinoma (positive) from mucinous adenocarcinoma (negative), while androgen receptor aids in differentiating salivary duct carcinoma (positive) from mucoepidermoid carcinoma (negative); and molecular testing plays a critical role in definitive diagnosis (e.g., the AKT1 E17K mutation for mucinous adenocarcinoma, MAML2 rearrangement for mucoepidermoid carcinoma, and MEF2C::SS18 fusion for microsecretory adenocarcinoma). This paper systematically summarizes the core pathological features and differential diagnostic points of mucin-rich salivary gland tumors, aiming to provide a practical reference for clinical pathological diagnosis.

Objective: To investigate the impact of activin receptor type-1 (ACVR1) on odontoblastic differentiation and dentin formation based on single-cell RNA sequencing. Methods: A correlation analysis of ACVR1 with odontogenesis-related transcription factors was performed using single-cell data from healthy wild-type adult mouse incisors obtained from the Gene Expression Omnibus database (GSE146123). This experiment was approved by the Institutional Animal Care and Use Committee of the affiliated institution. Conditional knockout mice with ACVR1 deleted in the dental mesenchyme were generated using the Cre-LoxP system (experimental group: Osterix-Cre; ACVR1fx/-, control group: Osterix-Cre; ACVR1fx/+). Dental pulp tissue was extracted from the incisors of 3-week-old mice to prepare single-cell suspensions for 10 × Genomics single-cell transcriptome sequencing. Quality control, normalization, dimensionality reduction, and Harmony batch effect correction were performed using the Seurat pipeline, followed by UMAP dimensionality reduction visualization and cell subpopulation identification. Monocle was used for pseudotime analysis to infer cell differentiation trajectories, and changes in transcription factors positively correlated with ACVR1 were analyzed at the single-cell data level. Immunofluorescence staining was employed to validate the localization and expression changes of the key transcription factor Osterix and the odontoblast-specific protein DSPP. Results: Sp7/Osterix is widely expressed in the incisor mesenchyme of mice (GSE146123). Using Osterix-Cre, ACVR1 was effectively knocked out in the mesenchyme. Gene correlation analysis between ACVR1 and key odontogenic genes showed positive correlations between ACVR1 and genes such as Msx1, Msx2, and Sp7. Single-cell atlases of incisor dental pulp tissue from “Osterix-Cre; ACVR1fx/-” and “Osterix-Cre; ACVR1fx/+” mice were then constructed. The most significant increase in the proportion of pre-odontoblasts was in the experimental group, along with downregulated expression of key genes related to odontoblastic differentiation and polarization in this subpopulation. Differential gene enrichment analysis across all mesenchymal subpopulations indicated downregulated expression of most genes associated with dentin formation. Finally, as observed through single-cell differential gene analysis, pseudotime expression analysis, and immunofluorescence validation, the expression of Sp7 and DSPP were significantly downregulated in the experimental group. Conclusion The ACVR1 gene may promote odontoblastic differentiation and subsequently affect dentin formation through transcription factors such as Sp7, Msx1, and Msx2.

Objective : To investigate the effects of angiopoietin 4 (ANGPT4) on the odontogenic differentiation of human dental pulp stem cells. Methods : This study has been reviewed and approved by the Ethics Committee, and informed consent has been obtained from patients. Human premolars were fixed, decalcified, dehydrated, embedded, and sectioned. Immunofluorescence staining was used to observe the expression and localization of ANGPT4. Human dental pulp stem cells (hDPSCs) were isolated and cultured in vitro. The growth state and morphology of hDPSCs were observed under an inverted phase contrast microscope. The expression of cell surface-related molecular markers was detected by flow cytometry. Alkaline phosphatase and alizarin red S staining were used to detect the odontogenic differentiation potential of hDPSCs. Oil-red O staining was used to detect the adipogenic differentiation potential of hDPSCs. RNA was extracted from hDPSCs at different time points after odontogenic induction, and RT-qPCR was used to analyze the mRNA expression of ANGPT4 and odontogenic-related genes during the odontogenic differentiation of hDPSCs in vitro. siRNA gene silencing technology was used to silence the expression of ANGPT4 in hDPSCs, and the silencing efficiency was detected by RT-qPCR and Western Blot. After silencing ANGPT4 in hDPSCs for 24 h, odontogenic induction was performed. Alkaline phosphatase and alizarin red S staining were performed on the 7th and 14th of induction to detect the odontogenic differentiation ability of hDPSCs after silencing ANGPT4 Results : Immunofluorescence staining of human premolars showed that ANGPT4 was expressed in odontoblasts and sub-odontoblastic cell-rich zone. hDPSCs were in good condition after 14 days of isolation and culture. Under the microscope, multiple cell colonies were observed, and the cell morphology was uniform and long spindle-shaped. The results of flow cytometry showed that hDPSCs expressed mesenchymal stem cell markers CD105 (90.42%) and CD90 (97.15%), but did not express hematopoietic cell markers CD45 (0.01%) and CD34 (0.08%). After odontogenic and adipogenic induction of hDPSCs, alkaline phosphatase staining, alizarin red S staining and oil red O staining were positive. The results of RT-qPCR after the odontogenic induction of hDPSCs showed that ANGPT4 was highly expressed on the 5th, 7th, 11th and 14th days of differentiation of hDPSCs (P<0.05), with the highest expression level on the 5th day. After hDPSCs were transfected with si-ANGPT4, the expression of ANGPT4 mRNA and protein was significantly down-regulated (P<0.05). The results of alkaline phosphatase staining showed that ALP staining intensity and area in the si-ANGPT4 group were significantly lower than those in the negative control. Alizarin red S staining showed that the formation of calcium nodules in the si-ANGPT4 group was significantly lower than that in the negative control. Conclusion ANGPT4 was expressed in odontoblasts and sub-odontoblastic cell-rich zone of human premolars. ANGPT4 may be a factor to promote the odontogenic differentiation of hDPSCs.