The molecular and functional heterogeneity of pancreatic β-cells is well recognized, but the underlying mechanisms remain unclear. Pancreatic islets harbor a subset of β-cells that co-express Tyrosine Hydroxylase (TH), an enzyme involved in synthesis of catecholamines that repress insulin secretion. Restriction of the TH+ β-cells within islets is essential for appropriate function in mice, such that higher proportion of these cells corresponds to reduced insulin secretion. Here, we use these cells as a model to dissect the developmental control of β-cell heterogeneity. We define the specific molecular and metabolic characteristics of TH+ β-cells, and show differences in their developmental restriction in mice and humans. We show that TH expression in β-cells is restricted by DNA methylation during β-cell differentiation. Ablation of de novo DNA methyltransferase Dnmt3a in the embryonic progenitors results in a dramatic increase in the proportion of TH+ β-cells, while β-cell specific ablation of Dnmt3a does not. We demonstrate that maintenance of Th promoter methylation is essential for its continued restriction in postnatal β-cells. Loss of Th promoter methylation in response to chronic overnutrition increases the number of TH+ β-cells, corresponding to impaired β-cell function. These results reveal a regulatory role of DNA methylation in determining β-cell heterogeneity.

<p>The molecular and functional heterogeneity of pancreatic b-cells is well recognized, but the underlying mechanisms remain unclear. Pancreatic islets harbor a subset of b-cells that co-express Tyrosine Hydroxylase (TH), an enzyme involved in synthesis of catecholamines that repress insulin secretion. Restriction of the TH+ b-cells within islets is essential for appropriate function in mice, such that higher proportion of these cells corresponds to reduced insulin secretion. Here, we use these cells as a model to dissect the developmental control of b-cell heterogeneity. We define the specific molecular and metabolic characteristics of TH+ b-cells, and show differences in their developmental restriction in mice and humans. We show that TH expression in b-cells is restricted by DNA methylation during b-cell differentiation. Ablation of <em>de novo</em> DNA methyltransferase Dnmt3a in the embryonic progenitors results in a dramatic increase in the proportion of TH+ b-cells, while b-cell specific ablation of Dnmt3a does not. We demonstrate that maintenance of <em>Th</em> promoter methylation is essential for its continued restriction in postnatal b-cells. Loss of <em>Th</em> promoter methylation in response to chronic overnutrition increases the number of TH+ b-cells, corresponding to impaired b-cell function. These results reveal a regulatory role of DNA methylation in determining b-cell heterogeneity.</p>

The molecular and functional heterogeneity of pancreatic β-cells is well recognized. Pancreatic islets harbor a small subset of β-cells that co-express Tyrosine Hydroxylase (TH), an enzyme involved in synthesis of catecholamines that repress insulin secretion. Restriction of this sub-population within islets is essential for appropriate insulin secretion. However, the distinguishing characteristics of this subpopulation and the mechanisms that restrict TH expression in β-cells are not known. Here, we define the specific molecular and metabolic characteristics of the TH+ β-cells and show that TH expression in β-cells is restricted by DNA methylation patterning during β-cell lineage specification. Ablation of de novo DNA methyltransferase Dnmt3a in the pancreatic- and endocrine-progenitor lineages results in a dramatic increase in the proportion of TH+ β-cells, while β-cell specific ablation of Dnmt3a has no effect on this sub-population. We demonstrate that maintenance of Th promoter DNA methylation patterns is essential for its continued restriction in postnatal β-cells, and that loss of DNA methylation dysregulates TH expression in β-cells in response to chronic overnutrition, contributing to impairment of β-cell identity. These data highlight the essential requirement of DNA methylation patterning in regulating endocrine cell fates, and reveal a novel role of DNA methylation in β-cell heterogeneity.

<p>The molecular and functional heterogeneity of pancreatic b-cells is well recognized, but the underlying mechanisms remain unclear. Pancreatic islets harbor a subset of b-cells that co-express Tyrosine Hydroxylase (TH), an enzyme involved in synthesis of catecholamines that repress insulin secretion. Restriction of the TH+ b-cells within islets is essential for appropriate function in mice, such that higher proportion of these cells corresponds to reduced insulin secretion. Here, we use these cells as a model to dissect the developmental control of b-cell heterogeneity. We define the specific molecular and metabolic characteristics of TH+ b-cells, and show differences in their developmental restriction in mice and humans. We show that TH expression in b-cells is restricted by DNA methylation during b-cell differentiation. Ablation of <em>de novo</em> DNA methyltransferase Dnmt3a in the embryonic progenitors results in a dramatic increase in the proportion of TH+ b-cells, while b-cell specific ablation of Dnmt3a does not. We demonstrate that maintenance of <em>Th</em> promoter methylation is essential for its continued restriction in postnatal b-cells. Loss of <em>Th</em> promoter methylation in response to chronic overnutrition increases the number of TH+ b-cells, corresponding to impaired b-cell function. These results reveal a regulatory role of DNA methylation in determining b-cell heterogeneity.</p>

<p>The molecular and functional heterogeneity of pancreatic b-cells is well recognized, but the underlying mechanisms remain unclear. Pancreatic islets harbor a subset of b-cells that co-express Tyrosine Hydroxylase (TH), an enzyme involved in synthesis of catecholamines that repress insulin secretion. Restriction of the TH+ b-cells within islets is essential for appropriate function in mice, such that higher proportion of these cells corresponds to reduced insulin secretion. Here, we use these cells as a model to dissect the developmental control of b-cell heterogeneity. We define the specific molecular and metabolic characteristics of TH+ b-cells, and show differences in their developmental restriction in mice and humans. We show that TH expression in b-cells is restricted by DNA methylation during b-cell differentiation. Ablation of <em>de novo</em> DNA methyltransferase Dnmt3a in the embryonic progenitors results in a dramatic increase in the proportion of TH+ b-cells, while b-cell specific ablation of Dnmt3a does not. We demonstrate that maintenance of <em>Th</em> promoter methylation is essential for its continued restriction in postnatal b-cells. Loss of <em>Th</em> promoter methylation in response to chronic overnutrition increases the number of TH+ b-cells, corresponding to impaired b-cell function. These results reveal a regulatory role of DNA methylation in determining b-cell heterogeneity.</p>