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Adult mouse islet: beta cells in red, alpha cells in green
The pancreas is a multifunctional organ and is susceptible to a myriad of diseases. We use a combination of in vivo mouse genetics, in vitro human-derived embryonic stem cell differentiations, and ex vivo pancreatic organoid cultures to define the mechanisms by which the pancreas develops, matures, and functions in health and disease with the ultimate goal of improving therapeutic treatments for pancreas disorders, like diabetes and agenesis. I am always open to new ideas and collaborations!
Benefits of using multiple models, adapted
Project 1: Synergy between Retinoic Acid (RA) signaling and GATA transcription factors that regulate pancreas development, function, and disease.
Project 1: Synergy between Retinoic Acid (RA) signaling and GATA transcription factors that regulate pancreas development, function, and disease.
RA is an essential signaling molecule in many developmental and adult contexts including during some of the earliest stages of pancreagenesis. Using a combination of mouse genetics and human embryonic stem cell derived beta-like cells, we demonstrated that RA signaling was also uniquely essential for pancreatic endocrine progenitor development, which occurs after initial pancreas specification (Lorberbaum et al., 2020).
The GATA transcription factors, like RA, are also important for many diverse developmental processes in mice and humans. GATA6 and GATA4 are the most critical for the pancreas. In fact, point mutations in GATA6 (in both coding and non-coding regions) are the most common cause of pancreas agenesis in patients. Amazingly, using either hiPSCs or hESC with patient specific mutations that lead to severe agenesis and neonatal diabetes, our collaborators demonstrated that beta cells were still generated in these mutant lines (Tiyaboonchai et al., 2017). A significant reduction in the number and function of beta cells was only observed when RA was simultaneously inhibited from these GATA6 impaired lines.
e16.5 cross section of a mouse pancreas with dual protein (IF)/ RNA (RNA-scope) staining: INS (green), SST (red), Sst (white).
I began following up these results as a postdoctoral fellow in the Sussel Lab by generating mutant mice that simultaneously had impaired RA signaling and GATA6 knocked out in a variety of cell types: pancreatic progenitors and endocrine progenitors using temporally and tissue specific CRE drivers. I have found substantial interactions between RA signaling and GATA6 that impair pancreas development and islet function. These compound mutants have beta, alpha, and delta cell defects that have a significant impact on adult metabolic function. This project seeks to use the tools mentioned here to define the mechanisms by which these RA/GATA interactions occur and fully define how this synergy impacts pancreas development and function. I have several hypotheses about how this interaction occurs and preliminary experiments suggesting a direct protein-protein interaction between GATA6 and the RA transcriptional effector RARa have already been completed. Further work characterizing co-regulation at the transcriptional level via CUT&RUN is also being actively pursued. This project is also supported by a K99/R00 fellowship from the NIH NIDDK.
e12.5 ventral (red, left), and dorsal (red, right) mouse pancreas
Project 2: Developmental origins of beta cell heterogeneity
Project 2: Developmental origins of beta cell heterogeneity
High throughput sequencing has allowed for in-depth analysis of beta cells and identification of transcriptomes indicating there are multiple types of insulin producing beta cells that can be reliably separated based on cell surface markers. The ratio of these beta cell subtypes are disrupted in people with diabetes, suggesting that these different subtypes are important for normal, healthy beta cell function. While this kind of heterogeneity has been identified repeatedly and in many different experiments, the origins remain unclear.
This project leverages in vivo genetic tools to test the hypothesis that distinct signaling events during early pancreas specification contribute to beta cell heterogeneity. The pancreas forms as separate dorsal and ventral buds that receive signals from two distinct sources: the dorsal aorta and notochord vs. the cardiac mesoderm, septum transversum, and hepatic endoderm. Around embryonic day 12.5 these buds fuse, allowing the pancreas to develop as a single organ. Even as a fully mature structure the pancreas is still divided into two regions: the head (derived from the ventral) and tail (derived from the dorsal). While both regions contain islets essential to maintaining blood glucose homeostasis, regional differences have been reported and the precise signals regulating those early, pre-fusion buds, have not been fully explored. For instance, RA signaling impairs dorsal pancreas development, but its role is ventral pancreas specification is not clear. Using the tools in my laboratory, I have generated a platform to clearly isolate each pancreatic bud and assess differences that could lead to islet heterogeneity in adults.
Pdx1:Cre; Tomato marks both lobes of the mouse pancreas (and the duodenum) before and after the dorsal and ventral buds fuse.
Additional Projects:
Additional Projects:
-Similarities and differences between mouse and human pancreas development and function.
-Similarities and differences between mouse and human pancreas development and function.
-RA/WNT/GATA interactions in pancreas development and disease
-Organoid and hPSC models of pancreas development and disease
-Dietary manipulation of Vitamin A (RA) in mice
Pancreatic organoids from mouse tissue
Mouse and Human Pancreas Development
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