Single-Cell RNA-seq Identifies Cell Diversity in Embryonic Salivary Glands

Abstract

Branching organs, including the salivary and mammary glands, lung, and kidney, arise as epithelial buds that are morphologically very similar. However, the mesenchyme is known to guide epithelial morphogenesis and to help govern cell fate and eventual organ specificity. We performed single-cell transcriptome analyses of 14,441 cells from embryonic day 12 submandibular and parotid salivary glands to characterize their molecular identities during bud initiation. The mesenchymal cells were considerably more heterogeneous by clustering analysis than the epithelial cells. Nonetheless, distinct clusters were evident among even the epithelial cells, where unique molecular markers separated presumptive bud and duct cells. Mesenchymal cells formed separate, well-defined clusters specific to each gland. Neuronal and muscle cells of the 2 glands in particular showed different markers and localization patterns. Several gland-specific genes were characteristic of different rhombomeres. A muscle cluster was prominent in the parotid, which was not myoepithelial or vascular smooth muscle. Instead, the muscle cluster expressed genes that mediate skeletal muscle differentiation and function. Striated muscle was indeed found later in development surrounding the parotid gland. Distinct spatial localization patterns of neuronal and muscle cells in embryonic stages appear to foreshadow later differences in adult organ function. These findings demonstrate that the establishment of transcriptional identities emerges early in development, primarily in the mesenchyme of developing salivary glands. We present the first comprehensive description of molecular signatures that define specific cellular landmarks for the bud initiation stage, when the neural crest–derived ectomesenchyme predominates in the salivary mesenchyme that immediately surrounds the budding epithelium. We also provide the first transcriptome data for the largely understudied embryonic parotid gland as compared with the submandibular gland, focusing on the mesenchymal cell populations.

p63 and Its Target Follistatin Maintain Salivary Gland Stem/Progenitor Cell Function through TGF-β/Activin Signaling

“…This analysis identified seven distinct groups of epithelial cells, which we visualized via uniform manifold approximation and projection (UMAP) ( Figure 4 A). Cell type assignments were made based on the expression of known/validated marker genes similar to what we and others have previously reported in both the SMG and PG ( Table S2 ) ( Song et al., 2018 ; Oyelakin et al., 2019 ; Sekiguchi et al., 2020 ). Integrated analysis of control and ΔNp63KO datasets revealed striking differences between the various cell populations ( Figure 4 B).…”

Generation of a Single-Cell RNAseq Atlas of Murine Salivary Gland Development

“…Although previous scRNAseq studies in salivary glands have started to uncover heterogeneity at defined timepoints ( Sekiguchi, et al., 2020 ; Oyelakin, et al., 2019 ; Song, et al., 2018 ), a major advance of our scRNAseq resource is the inclusion of discrete developmental landmarks that will inform future studies on the mechanisms that regulate the development of branching organs, particularly salivary glands. These data add to our previous microarray analysis of SMG development and are available in the Salivary Gland Molecular Anatomy Project (SGMAP, https://sgmap.nidcr.nih.gov ).…”

Transcriptional Landscaping Identifies a Beige Adipocyte Depot in the Newborn Mouse

“…However, some fat cell lineages, including BAT adipocytes, are derived from the embryonic ectoderm [ 90 ], which is rich in keratin expression [ 91 ]. Moreover, Krt5 is expressed by myoepithelial progenitors [ 92 ], and BAT fat cells have been shown to develop from myoepithelial cells in the mammary gland [ 93 ] where epithelium-to-adipocyte transdifferentiation might occur [ 94 , 95 ]. It is known that Krt19 is expressed by mouse preadipocytes, and in vitro adipocyte differentiation is associated with an increment in Krt19 expression [ 46 ].…”