Identification of distinct functions of GLIS3 in β-cell generation critical to prevention of neonatal diabetes.

GLIS3 plays a critical role in pancreatic β cells and diabetes, being one of only a few genes implicated in Type 1, Type 2, and Gestational diabetes. In addition to β cells, GLIS3 is expressed embryonically in bipotent and proendocrine progenitor cells, suggesting a role in endocrine lineage development in mice. We hypothesize that GLIS3 is playing important roles in endocrine development as well as during β cell differentiation. We utilized single cell RNA-sequencing at three different timepoints (embryonic day (e)13.5, e15.5, and e18.5) and single nucleus (sn)ATAC-sequencing at e15.5 in both wild type (WT) and Glis3 Knockout (Glis3KO) mouse embryos. This analysis revealed that the numbers of bipotent, proendocrine progenitor, and all subsequent endocrine cells were proportionately reduced in Glis3KO mice. Additionally, loss of GLIS3 function generates a unique subpopulation of cells that fail to upregulate Ins2 transcription and downregulate expression of several ribosomal and oxidative phosphorylation genes normally repressed during preβ to β cell differentiation. Our study therefore shows that GLIS3 regulates two distinct stages: the embryonic generation/differentiation of bipotent cells and the differentiation of preβ to β cells. Dysregulation of these two stages provides a causal mechanism for the development of neonatal diabetes in GLIS3-deficiency.