Pancreatic cell lineage and genes required for endocrine islet formation.
Investigating pancreatic beta cell production and function
The vertebrate pancreas includes exocrine and endocrine tissues that are responsible for digesting food and regulating sugar metabolism, respectively. Several diseases associate with the pancreas, including pancreatitis, diabetes, and pancreatic cancer, amongst which diabetes is the most prevalent that inflicts more than 27 million individuals in the United States.
We investigate the cellular and molecular mechanisms underlying islet cell differentiation and function, which include multiple endocrine cell types that secrete insulin (beta cells), glucagon (alpha cells), somatostatin (delta cells), and pancreatic polypeptide (PP cells), respectively. Our basic strategy is to first unambiguously identify progenitors of each specific cell type, then examine the molecular networks and cellular interactions for their development and function. Our studies focus on the following areas:
1. Technology development: A challenge of studying development and organogenesis in mammals is our inability to follow specific cells during their development to understand thwir specification and function. The Cre-Lox-based technology allows for temporal and spatial cell marking and gene activity manipulation, with a drawback of marking all cells that express Cre that includes multiple cell types. We have engineered two inactive Cre fragments that can reconstitute Cre in cells that simultaneously express dual protein markers. This enabled the identification of beta-cell progenitor cells and high-resolution analysis of the genetic/epigenetic programs that direct the production of functional beta cells. It also allows us to examine how seemingly identical progenitor cells adopt different cell fate, either as pre-deterministic or stochastic model. In the former possibility, progenitor may have differential gene expression and differentiation potentials. In the later model, progenitor cells are identical, yet stochastic transcription of certain factors could bias progenitors to specific cell fate.
2. Novel mode of cell-cell communication for coordinated cellular differentiation: Notch-mediated cell-cell interactions were known to select a specific set of pancreatic cells as endocrine progenitors by activating the expression of Ngn3. Yet Notch signaling alone cannot account for the coordinated differentiation of neighboring cells adopt islet cell fate at same time windows. We have shown that gap junction-mediated information can control this coordinated differentiation. We are currently exploring whether miRNA-based mechanism coordinate endocrine cell differentiation through gap junctions, aided by RNASeq- and miRNAseq-based techniques.
3. Differentiation, survival, and function. With state-of-the-art technologies such as FACS-based cell sorting, RNAseq, and CHIPseq, we purify intermediate cell populations that have defined function and examine the genetic networks that direct cell differentiation and function. These studies avoid complications caused by unwanted cell types in tissue samples. We have identified several previously unidentified gene circuits that might participate endocrine differentiation and their role in islet production are being examined. We also identify factors that maintain beta cell survival during their function and stress, such as the Myt1 family of transcription factors. Lastly, we investigate how cellular structures, such as microtubules, direct beta cell function, in insulin vesicular transport and secretion. We are currently working on a hypothesis that microtubules in pancreatic beta cells act as a storage structure to fine-tune insulin secretion.
Postdoctoral Positions Available
One postdoctoral position available for studying endocrine islet cell development. Available projects includes: 1) characterizing genes expression during mouse pancreas development; 2) generating transgenic and knockout mice to evaluate gene function for endocrine islet development, beta cell maturation, and functional maintenance; 3) using chicken embryos to screen for genes required for endocrine cell differentiation, and 4) using cell lineage tracing methods to understand islet homeostasis and adult pancreatic stem/progenitor cells.