Comparative RNA-seq Sheds Light on Functional Differentiation of Human Major Salivary Glands

Objectives: Saliva aids in pre-digestion of food and taste perception, helps to maintain the integrity of the mineralized tooth and epithelial surfaces in the mouth, and shields the oro-digestive tract from environmental hazards and invading pathogens. Although salivary glands and salivary fluid are biologically and functionally inseparable, they have thus far been investigated as separate entities.
Methods: To bridge this gap, we report an integrative analysis of RNAseq data from 27 salivary gland samples collected from adult and fetal submandibular, sublingual, and parotid glands along with mass-spectrometry-based proteome data and immunohistochemical localization in gland tissue.
Results: Our results suggest that gland differentiation at the transcriptome level occurs after the glands are anatomically separated, and is driven mainly by the transcription of genes that code for secreted saliva proteins. We further found a clear concordance of RNA levels with corresponding protein abundances, suggesting that protein dosage of the proteins secreted by salivary glands is predominantly regulated at the transcriptome level.
Conclusions: Our study provides the hitherto most comprehensive dataset of RNAseq of healthy salivary glands in humans, creating a robust framework for investigating biology, development, and evolution of salivary glands and their protein products. By doing so, it paves the way for a better understanding of their functions in health and malfunctions in disease.