Abstract: FR-PO922
Modulation of Lef/Tcf Activity in Response to Differential β-Catenin Levels Underlies Nephron Progenitor Differentiation
Session Information
- Development, Stem Cells, Regenerative Medicine - II
October 26, 2018 | Location: Exhibit Hall, San Diego Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Development, Stem Cells, and Regenerative Medicine
- 501 Development, Stem Cells, and Regenerative Medicine: Basic
Authors
- Guo, Qiuyu, University of Southern California , Los Angeles, California, United States
- Kim, Albert D., University of Southern California, Los Angeles, California, United States
- Tran, Trinh k (tracy), University of Southern California, Los Angeles, California, United States
- Lindstrom, Nils, The University of Southern California, Los Angeles, California, United States
- Brown, Aaron C., Maine Medical Center Research Institute, Scarborough, Maine, United States
- Oxburgh, Leif, Maine Medical Center Research Institute, Scarborough, Maine, United States
- McMahon, Andrew P., Keck School of Medicine of the University of Southern California, Los Angeles, California, United States
Group or Team Name
- The McMahon Laboratory
Background
The Wnt9b ligand and β-catenin are required for both nephron progenitor cell (NPC) self-renewal and differentiation (Carrol et al., 2005; Park et al., 2007; Karner et al., 2011). Though high Wnt pathway activity stimulates NPC commitment, stabilized β-catenin binds to enhancers regulating both self-renewal and NPC differentiation targets, with opposing transcriptional outcomes (Park et al., 2012). How different levels of β-catenin result in distinct outcomes for NPCs remains to be determined.
Methods
To investigate the molecular mechanism behind Wnt/β-catenin-driven NPC self-renewal and differentiation, we modeled the two processes in vitro in NPEM culture medium (Brown et al., 2015) which enables NPC expansion when supplemented with low levels of CHIR99021 (CHIR), a β-catenin agonist, and NPC differentiation with elevated CHIR levels. Gene expression and epigenetic profiles were determined by bulk RNA-Seq and ATAC-Seq, followed up with immunohistochemistry on key targets-of-interest. To directly map genomic targets of Lef/Tcf factors and β-catenin, we performed ChIP-Seq on NPCs under expansion and differentiation conditions.
Results
RNA-Seq and immunohistochemistry data suggests differential expression levels of Lef/Tcf factors between NPC cultured in low and high levels of CHIR. In the high CHIR condition, the transcriptional repressor Tcf7l1 is down-regulated, while the activators Tcf7 and Lef1 are up-regulated. ATAC-Seq analysis showed strong enrichment of Tcf/Lef footprint in open chromatin regions specific to high CHIR condition, suggesting a role of β-catenin in activating relevant enhancers. Direct ChIP-Seq for Lef/Tcf factors showed a rapid replacement of Tcf7l1/Tcf7l2 repressors by Tcf7/Lef1 activators at enhancers for differentiation target genes on stabilization of β-catenin.
Conclusion
We propose a model wherein Tcf7l1/Tcf7l2 repressors maintain NPC self-renewal state by silencing enhancers involved in differentiation and β-catenin stabilization triggers a switch promoting the engagement of Tcf7/Lef1 activators. This state is reinforced by a positive feedback loop where Lef1 is a target of itself. Given the widespread role of Wnt signaling in stem/progenitor cell programs, these findings are likely to have broader significance beyond the mammalian kidney.
Funding
- NIDDK Support