Kidney Week

Abstract: TH-OR082

Polycomb Repressive Complex-2 (PRC2) Fine-Tunes Timing of the Final Wave of Nephrogenesis

Session Information

• Novel Mechanisms and Pathways in Kidney Development
  November 02, 2017 | Location: Room 385, Morial Convention Center
  Abstract Time: 05:18 PM - 05:30 PM

Category: Developmental Biology and Inherited Kidney Diseases

• 401 Developmental Biology

Authors

• El-Dahr, Samir S., Tulane University School of Medicine, New Orleans, Louisiana, United States

Samir S. El-Dahr, MD

• Saifudeen, Zubaida R., Tulane University School of Medicine, New Orleans, Louisiana, United States

Zubaida R. Saifudeen,

• Liu, Hongbing, Tulane , New Orleans, Louisiana, United States

Hongbing Liu,

Background

The mechanisms that control cessation of nephrogenesis are not well understood. Heterochronic transplantation and epigenome profiling suggest that old nephron progenitor cells (NPC) are poised for differentiation limiting their lifespan. In stem cells, Enhancers of Zeste, Ezh1 and Ezh2, the catalytic components of PRC2, mediate H3K27 methylation to maintain lineage-specific genes in a silent yet poised state. We hypothesized that PRC2 activity restrains NPC aging and is essential for timely cessation of nephrogenesis.

Methods

We generated conditional Six2^Ezh2-/-; ROSA26^Tomato and compound Six2^Ezh2-/-;Ezh1^-/-;ROSA26^Tomato mice. Molecular and phenotypic analyses were accomplished by section IF and ISH at E15.5, E17.5, and P0, and transcriptome profiling of Six2-GFP⁺ cells at E17.5. Results were integrated with genome-wide maps of accessible chromatin, Six2 and histone mark occupancy, and scRNA-seq databases.

Results

Six2^Ezh2-/- and germline Ezh1^-/- kidneys are morphologically normal. In contrast, E17.5 Six2^Ezh2-/-;Ezh1^-/- and Six2^Ezh2-/-;Ezh1^+/- NPC fail to form the cap mesenchyme and display a unique gene expression signature consisting of the cell cycle inhibitor Cdkn2a/p16, Lin28B (inhibitor of Let-7 miRNA upregulated in Wilm’s tumor), Six1 (normally expressed in early metanephric mesenchyme but absent in mouse cap mesenchyme), Hoxd13 and Wnt5A/10A genes. In wild-type NPC, these aberrantly expressed genes are silent and heavily methylated on H3K27, yet display small peaks of accessible chromatin suggesting a state of epigenetic poising. At P0, Six2^Ezh2-/-;Ezh1^+/- NPC undergo en mass differentiation into ectopic Tomato⁺/Wnt4⁺/Pax2⁺/Lef1⁺/Lhx1⁺ renal vesicles located dorsal to the UB tips, akin to the final wave of nephrogenesis that normally occurs at P2-P4. There was complete loss of H3K27me3 in double Ezh1/Ezh2 mutant NPC and their derived epithelial tubules.

Conclusion

We conclude that H3K27 methylation fine-tunes timing of the last wave of nephrogenesis by restraining Cdkn2a/p16 and unscheduled activation of canonical Wnts in NPC. Ectopic induction of Lin28B, Hox and Six1 in mutant progenitors suggests a state of arrested differentiation of metanephric mesenchyme. Interventions targeting PRC2 function may be beneficial for nephron progenitor maintenance and regeneration.

Funding

• NIDDK Support