Loss of Epigenetic Regulation by Polycomb Repressive Complex 2 Results in Congenital Malformations of the Urogenital System
Catherine M. Seager, MD1, Mary Taglienti, MS1, Feng Shen, PhD2, Jordan Kreidberg, MD, PhD1.
1Boston Children's Hospital, Boston, MA, USA, 2Washington University School of Medicine, St. Louis, MO, USA.
Background: Congenital anomalies of the kidney and urinary tract represent a major cause of renal impairment in the pediatric population. We are investigating the role of epigenetics in the development of the urogenital system with the goal of understanding how impaired epigenetic regulation may lead to congenital anomalies such as ureteropelvic junction obstruction and ureterovesical junction obstruction. Reciprocal epithelial mesenchymal inductive interactions are critical to normal development of the kidney and the lower urogenital tract. The ureteric bud gives rise to the epithelium (inner compartment) of the collecting system while the smooth muscle and fibroblasts of the ureter (outer compartment) are derived from a TBX-18 expressing mesenchymal progenitor. Polycomb Repressive Complex 2 (PRC2) represses gene expression by placing trimethylation marks on histone three, thereby resulting in a closed chromatin state. Deletion of Eed, an essential component of the PRC2 complex, allows for inactivation PRC2.
Methods: We used gene targeting in mice to delete the Eed gene during development. Specifically, Eed was inactivated in either the epithelial or the mesenchymal compartment of the collecting system and ureter using HoxB7-Cre or TBX18-Cre respectively. Kidneys and lower urogenital tract phenotypes were characterized through histological and gene expression analyses. Functional assessment of drainage was performed by ink injection study.
Results: Conditional inactivation of Eed in the epithelium (Eed flox/flox;HoxB7-Cre) resulted in animals with severe bilateral hydroureteronephrosis by postnatal day 21 (P21) and ink injection studies suggested impaired drainage at the level of the bladder. Kidneys from Eed flox/flox;HoxB7-Cre mice at P1 were decreased in size as compared to controls, indicating that correct epigenetic regulation in the ureteric bud lineage is necessary for the maintenance of nephrogenesis. Six2 expression, which is required for maintenance of nephron progenitor cells, was found to be reduced by E15.5. This was accompanied by decreases in known regulators of nephrogenesis and cortico-medullary axis formation including Bmp7, Wnt9b and Wnt7b.
Conditional inactivation of Eed in the ureteral mesenchymal progenitors (Eed flox/flox;TBX18-Cre) resulted in bilateral hydroureteronephrosis by P21. Ink injection studies showed impaired drainage at the level of the ureteropelvic junction. This was accompanied by increased expression of smooth muscle actin (SMA) and SM22-alpha at the UPJ.
Conclusions: Inactivation of the Eed gene in epithelial and mesenchymal cell-type progenitors of the ureter and collecting system results in abnormalities in ureteral and renal development that are accompanied by changes in gene expression. These studies are providing insights into how urogenital anomalies in humans may be caused by abnormal epigenetic regulation of gene expression during fetal and early postnatal development.
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