Single-cell ATAC-seq reveals OVOL2 as a downstream negative regulator of PRL-mediated proliferation in β cells

Maternal pancreatic β cells undergo functional and structural changes to adapt to increased metabolic demands during pregnancy. Lactogen signaling via the prolactin receptor (PRLR) contributes to these adaptations by increasing β-cell mass, insulin transcription, and glucose-stimulated insulin secretion. In other lactogen-responsive tissues such as the mammary glands and specific hypothalamic nuclei, gestation induces epigenetic changes, some of which persist long after birth. We have previously found that PRL treatment in islets regulates the expression of epigenetic modifiers. However, whether lactogen signaling in β cells mediates epigenetic changes to regulate chromatin accessibility has not been examined. Therefore, our objective was to determine whether PRLR signaling alters chromatin accessibility of β cells to facilitate transcriptional regulation. Using single-cell assay for transposase-accessible chromatin using sequencing (scATAC), we identified differentially accessible regions (DARs) in β cells that had 718 overrepresented motifs following PRL treatment of murine islets. Validating this approach, these included motifs bound by established PRLR signaling effectors such as the STAT family of transcription factors (TFs). Using RNA-sequencing we identified transcriptional changes in 41 TFs whose motifs were overrepresented in DARs, including several previously linked to PRLR signaling within β cells, including Myc, Mafb, and Esr1. Importantly, we also identified TFs not previously associated with PRLR signaling, including OVOL2, an established regulator of epigenetic landscape within cells. OVOL2 is a TF involved in epithelial to mesenchymal transition inhibition and energy homeostasis with unknown roles in pancreatic β cells. Here, we establish that OVOL2 acts as a negative regulator of lactogen-dependent effects on β-cell proliferation, establishing a novel regulator of PRLR signaling.