Temporal Transcriptome Analysis Reveals Dynamic Gene Expression Patterns Driving Beta-Cell Maturation

Newly differentiated pancreatic beta cells lack proper insulin secretion profiles of mature functional beta cells. The global gene expression differences between paired immature and mature beta cells have been studied, but the dynamics of transcriptional events, correlating with temporal development of glucose-stimulated insulin secretion (GSIS), remain to be fully defined. This aspect is important to identify which genes and pathways are necessary for beta-cell development or for maturation, as defective insulin secretion is linked with diseases such as diabetes. In this study, we assayed through RNA sequencing the global gene expression across six beta-cell developmental stages in mice, spanning from beta-cell progenitor to mature beta cells. A computational pipeline then selected genes differentially expressed with respect to progenitors and clustered them into groups with distinct temporal patterns associated with biological functions and pathways. These patterns were finally correlated with experimental GSIS, calcium influx, and insulin granule formation data. Gene expression temporal profiling revealed the timing of important biological processes across beta-cell maturation, such as the deregulation of beta-cell developmental pathways and the activation of molecular machineries for vesicle biosynthesis and transport, signal transduction of transmembrane receptors, and glucose-induced Ca2+ influx, which were established over a week before beta-cell maturation completes. In particular, beta cells developed robust insulin secretion at high glucose several days after birth, coincident with the establishment of glucose-induced calcium influx. Yet the neonatal beta cells displayed high basal insulin secretion, which decreased to the low levels found in mature beta cells only a week later. Different genes associated with calcium-mediated processes, whose alterations are linked with insulin resistance and deregulation of glucose homeostasis, showed increased expression across beta-cell stages, in accordance with the temporal acquisition of proper GSIS. Our temporal gene expression pattern analysis provided a comprehensive database of the underlying molecular components and biological mechanisms driving beta-cell maturation at different temporal stages, which are fundamental for better control of the in vitro production of functional beta cells from human embryonic stem/induced pluripotent cell for transplantation-based type 1 diabetes therapy.