A Systems Biology Approach Identifies a Regulatory Network in Parotid Acinar Cell Terminal Differentiation

Abstract

ObjectiveThe transcription factor networks that drive parotid salivary gland progenitor cells to terminally differentiate, remain largely unknown and are vital to understanding the regeneration process.MethodologyA systems biology approach was taken to measure mRNA and microRNA expression in vivo across acinar cell terminal differentiation in the rat parotid salivary gland. Laser capture microdissection (LCM) was used to specifically isolate acinar cell RNA at times spanning the month-long period of parotid differentiation.ResultsClustering of microarray measurements suggests that expression occurs in four stages. mRNA expression patterns suggest a novel role for Pparg which is transiently increased during mid postnatal differentiation in concert with several target gene mRNAs. 79 microRNAs are significantly differentially expressed across time. Profiles of statistically significant changes of mRNA expression, combined with reciprocal correlations of microRNAs and their target mRNAs, suggest a putative network involving Klf4, a differentiation inhibiting transcription factor, which decreases as several targeting microRNAs increase late in differentiation. The network suggests a molecular switch (involving Prdm1, Sox11, Pax5, miR-200a, and miR-30a) progressively decreases repression of Xbp1 gene transcription, in concert with decreased translational repression by miR-214. The transcription factor Xbp1 mRNA is initially low, increases progressively, and may be maintained by a positive feedback loop with Atf6. Transfection studies show that Xbp1Mist1 promoter. In addition, Xbp1 and Mist1 each activate the parotid secretory protein (Psp) gene, which encodes an abundant salivary protein, and is a marker of terminal differentiation.ConclusionThis study identifies novel expression patterns of Pparg, Klf4, and Sox11 during parotid acinar cell differentiation, as well as numerous differentially expressed microRNAs. Network analysis identifies a novel stemness arm, a genetic switch involving transcription factors and microRNAs, and transition to an Xbp1 driven differentiation network. This proposed network suggests key regulatory interactions in parotid gland terminal differentiation.

A single transcription factor is sufficient to induce and maintain secretory cell architecture

“…MIST1 is expressed in multiple long-lived secretory cells derived from every germ layer along numerous different lineage specification sequences (Schwab et al 2000;Pin et al 2001;Johnson et al 2004;Capoccia et al 2011;Metzler et al 2015). The principal common feature among those cells is not how they differentiate but what they do: secrete large amounts of protein over a long life span.…”

“…The XBP1 → MIST1 cassette is required in secretory cells of diverse tissues to establish the cargogenerating, packaging, and secreting machinery for professional secretory cells (Metzler et al 2015). The epithelium of the body of the stomach is a good model for studying cell fate-determining transcription factors versus scaling factors because it is organized into roughly tubular invaginations (units) with distinct zones of cell types and a stem cell that actively generates all of the cell types throughout life (Mills and Shivdasani 2011;Willet and Mills 2016).…”

The big and intricate dreams of little organelles: Embracing complexity in the study of membrane traffic

“…XBP1 is a transcription factor involved in the unfolded protein response in the ER; however, XBP1 plays a specialized role in acinar cells of pancreas and salivary glands by upregulating the biosynthetic machinery . Indeed, XBP1 −/− knockout mice with a XBP1 “knock‐in” in liver to rescue embryonic lethality showed a profound defect in ER and zymogen granule biogenesis .…”

“…The pancreas and salivary glands host specialized secretory tissues XBP1 is a transcription factor involved in the unfolded protein response in the ER; however, XBP1 plays a specialized role in acinar cells of pancreas and salivary glands by upregulating the biosynthetic machinery. 142,[145][146][147] Indeed, XBP1 −/− knockout mice with a XBP1…”

A systems biology approach identifies a gene regulatory network in parotid acinar cell differentiation.

“…Using these measurements we developed a gene expression network model incorporating both transcription factors and microRNAs driving expression of terminal differentiation markers, genes that would need to be expressed in regenerated or regrown acinar cells [113,114]. We validated several of these network interactions in ParC5 cells, a model of dedifferentiated parotid acinar cells.…”