Swi/Snf chromatin remodeling activity is required for islet cell development in vivo - PROJECT SUMMARY: Type 2 diabetes is associated with loss of activity and expression of pancreas-enriched
transcription factors (TFs) that control gene expression programs necessary for mature β-cell function. Among
these is Pdx1, which plays key roles during early pancreas development, islet endocrine cell differentiation, and
β-cell development and function. Pdx1, like most TFs, requires additional regulation from recruited coregulators
to modulate specific regulatory programs. Numerous coregulators have been identified as Pdx1-interacting
partners including the ATP-dependent Swi/Snf chromatin remodeling complex. In the early developing pancreas,
Swi/Snf plays a critical role in progenitor cell expansion, where early pancreatic progenitor cell deletion of one
essential Swi/Snf ATPase subunit, Brg1, results in a 50% reduction in final pancreas mass. In the mature β-cell,
deletion of both Swi/Snf ATPase subunits, Brg1 and Brm, impairs whole-body glucose tolerance through severe
loss of insulin production, which is largely driven by a loss of Pdx1 occupancy on the insulin gene promoter.
While Swi/Snf plays an essential role in the early developing pancreas and the mature β-cell, the contribution of
Swi/Snf chromatin remodeling activity to islet endocrine progenitor development has not yet been explored.
Herein, I will test the hypothesis that the Pdx1-recruited Swi/Snf chromatin remodeling complex
dynamically controls the chromatin landscape and expression of genes essential for endocrine
progenitor cell development and postnatal islet function. Mutant mice with endocrine-specific deletions of
either Brg1, Brm, or both subunits were generated to determine the mechanistic actions of Swi/Snf at this stage
of islet development and evaluate the postnatal consequences of losing Swi/Snf during islet endocrine cell
development. Preliminary results demonstrate that loss of the Brg1 subunit, but not Brm, from endocrine
progenitors leads to severe glucose dyshomeostasis beginning at 4 weeks of age with a reduction in plasma
insulin levels, suggesting that Brg1 is essential for proper islet development and function. Remarkably, no mice
deficient for both subunits have been recovered at weaning, indicating that total loss of Swi/Snf activity results
in postnatal lethality. Aim 1 will explore the anatomical and physiological attributes driving the postnatal
phenotype observed in the Swi/Snf mutants through quantitation of islet cell mass and evaluation of islet function
through perifusion analysis on isolated islets. Aim 2 will investigate the mechanistic actions of Swi/Snf in
controlling chromatin accessibility, TF recruitment, and gene expression programs in endocrine progenitor cells
with RNA-sequencing, ATAC-sequencing, and ChIP-qPCR approaches. With this F31 Predoctoral Fellowship, I
will be able to commit my time to completing the research described in the Aims outlined in this application, while
also focusing on career development and enhancing my scientific skillset through attending seminars and
workshops. Indiana University School of Medicine is equipped with experienced faculty and state-of-the-art core
facilities to assist in carrying out this research proposal and provide guidance in my training.
