Identification of Cell Types that Define Embryonic Submandibular and Parotid Salivary Glands Using Single Cell RNA Sequencing
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Branching organs including the kidney, mammary, and salivary glands 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 identify the molecular identities of the cells of submandibular versus parotid salivary glands during bud initiation. The gene expression of patterns of 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 well defined clusters according to the gland. Neuronal and muscle cells of the two glands expressed distinct markers and localization patterns. A muscle cluster was more prominent in the parotid, which was not myoepithelial or vascular smooth muscle. Instead, the muscle cluster expressed genes that are associated with 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 the establishment of transcriptional identities that emerge early, primarily in the mesenchyme of developing salivary glands. We present the first transcriptome data of the largely understudied embryonic parotid gland in relation to the submandibular gland, which has been the predominant salivary gland research model. Our study also provides the first comprehensive description of molecular signatures that define specific cellular landmarks for the bud initiation stage of these early branching organs.
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Introduction -- Background -- Preparation of Cells From Embryonic Organs for Single Cell RNA-Sequencing -- Single Cell Transcriptome Analyses Reveal Insights Into Embryonic Salivary Cell Identities -- Conclusions
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Ph.D. (Doctor of Philosophy)