Ablation of the Renal Stroma Defines Its Critical Role in Nephron Progenitor and Vasculature Patterning

Abstract

The renal stroma is an embryonic cell population located in the cortex that provides a structural framework as well as a source of endothelial progenitors for the developing kidney. The exact role of the renal stroma in normal kidney development hasn't been clearly defined. However, previous studies have shown that the genetic deletion of Foxd1, a renal stroma specific gene, leads to severe kidney malformations confirming the importance of stroma in normal kidney development. This study further investigates the role of renal stroma by ablating Foxd1-derived stroma cells themselves and observing the response of the remaining cell populations. A Foxd1cre (renal stroma specific) mouse was crossed with a diphtheria toxin mouse (DTA) to specifically induce apoptosis in stromal cells. Histological examination of kidneys at embryonic day 13.5–18.5 showed a lack of stromal tissue, mispatterning of renal structures, and dysplastic and/or fused horseshoe kidneys. Immunofluorescence staining of nephron progenitors, vasculature, ureteric epithelium, differentiated nephron progenitors, and vascular supportive cells revealed that mutants had thickened nephron progenitor caps, cortical regions devoid of nephron progenitors, aberrant vessel patterning and thickening, ureteric branching defects and migration of differentiated nephron structures into the medulla. The similarities between the renal deformities caused by Foxd1 genetic knockout and Foxd1DTA mouse models reveal the importance of Foxd1 in mediating and maintaining the functional integrity of the renal stroma.

Stromal Fat4 acts non-autonomously with Dachsous1/2 to restrict the nephron progenitor pool

“…Recently, a stromaless kidney ( produced by expression of diphtheria toxin in the Foxd1 lineage) was shown to phenocopy Fat4 nulls (Das et al, 2013;Hum et al, 2014). Owing to complete removal of the stromal compartment, the authors were unable to determine if a single molecular factor was responsible for the increased CM observed.…”

“…Stromal cells regulate both UB renal branching and the balance between self-renewal and nephron differentiation of the CM (Batourina et al, 2001;Das et al, 2013;Hatini et al, 1996;Hum et al, 2014;Levinson et al, 2005;Mendelsohn et al, 1999Mendelsohn et al, , 1994Paroly et al, 2013). Loss of the stromal transcription factor gene Foxd1 results in reduced branching and an expanded CM (Hatini et al, 1996).…”

A Fat4-Dchs1 signal between stromal and cap mesenchyme cells influences nephrogenesis and ureteric bud branching

“…2A-D). Increased thickness and disorganization of CM has also been noted in kidneys with stromal deletion, or mutation of Ecm1, Foxd1 or Fat4 (Das et al, 2013;Hatini et al, 1996;Hum et al, 2014;Levinson et al, 2005;Paroly et al, 2013).…”

“…The CM is surrounded by stroma. Genetic ablation of stromal cells or mutation of stromal-expressed genes, including Ecm1, Foxd1 and Fat4, has revealed that stroma influences the development of the CM and UB (Das et al, 2013;Hatini et al, 1996;Hum et al, 2014;Levinson et al, 2005;Paroly et al, 2013). Nonetheless, there remain substantial gaps in our understanding of the cellular and molecular mechanisms that orchestrate the communication between stromal cells and other cell layers required for kidney morphogenesis.…”

“…Differentiation of nephron progenitor cells (CM) into nephrons was reported to be defective in Fat4 mutants (Das et al, 2013), reminiscent of the effect of stromal cell ablation on CM differentiation (Das et al, 2013;Hum et al, 2014), and it was suggested that Fat4 participates in stromal-to-CM signaling. The inhibition of nephron progenitor cell differentiation in Fat4 mutants was attributed to increased Yap activity (Das et al, 2013), although how this might be achieved is unclear, as the molecular pathway linking Fat to Yap identified in Drosophila does not appear to be conserved in mammals (Bossuyt et al, 2014;Pan et al, 2013).…”