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

Abstract

Regulation of the balance between progenitor self-renewal and differentiation is crucial to development. In the mammalian kidney, reciprocal signalling between three lineages (stromal, mesenchymal and ureteric) ensures correct nephron progenitor self-renewal and differentiation. Loss of either the atypical cadherin FAT4 or its ligand Dachsous 1 (DCHS1) results in expansion of the mesenchymal nephron progenitor pool, called the condensing mesenchyme (CM). This has been proposed to be due to misregulation of the Hippo kinase pathway transcriptional co-activator YAP. Here, we use tissuespecific deletions to prove that FAT4 acts non-autonomously in the renal stroma to control nephron progenitors. We show that loss of Yap from the CM in Fat4-null mice does not reduce the expanded CM, indicating that FAT4 regulates the CM independently of YAP. Analysis of Six2 −/− ;Fat4 −/− double mutants demonstrates that excess progenitors in Fat4 mutants are dependent on Six2, a crucial regulator of nephron progenitor self-renewal. Electron microscopy reveals that cell organisation is disrupted in Fat4 mutants. Gene expression analysis demonstrates that the expression of Notch and FGF pathway components are altered in Fat4 mutants. Finally, we show that Dchs1, and its paralogue Dchs2, function in a partially redundant fashion to regulate the number of nephron progenitors. Our data support a model in which FAT4 in the stroma binds to DCHS1/2 in the mouse CM to restrict progenitor self-renewal.

Fat4-Dchs1 signalling controls cell proliferation in developing vertebrae

“…Fat/Fat4 regulation of cell behaviours through PCP has been shown to be conserved (Saburi et al, 2008;Mao et al, 2011Mao et al, , 2016Zakaria et al, 2014). Evidence linking Fat4/Dchs1 to the Hippo pathway is less clear (Cappello et al, 2013;Das et al, 2013;Mao et al, 2015;Bagherie-Lachidan et al, 2015). Here we show that Fat4-Dchs1 controls cell proliferation within the developing sclerotome.…”

“…This lack of interaction between Fat4 and Yap/Taz has also been observed in the kidney (Mao et al, 2015;Bagherie-Lachidan et al, 2015), indicating distinct mechanisms of Fat4-Dchs1 signalling during vertebrate development. Indeed, there is currently very little, if any, evidence of a direct link between Fat4 and Hippo signalling in vertebrates.…”

“…Fat4 regulation of Yap intracellular localisation within the pre-nephrogenic precursors has also been observed (Das et al, 2013). However, other studies have reported that Fat4 does not regulate Yap localisation and activity in the kidney (Mao et al, 2015;Bagherie-Lachidan et al, 2015).…”

“…Based on potential conservation between Drosophila and mammals it has been proposed that Fat4-Dchs1 regulates PCP and the Hippo pathway. Conservation of PCP has clearly been shown in the hindbrain and kidney but conservation of Fat4-Hippo signalling is controversial (Cappello et al, 2013;Das et al, 2013;Zakaria et al, 2014;Mao et al, 2015;Bagherie-Lachidan et al, 2015). We have previously reported that Fat4 and Dchs1 mutants are characterised by wider vertebrae that are also fused along the anterior-posterior axis, raising the possibility that alterations in polarised cell behaviours contribute to this phenotype (Mao et al, 2011).…”

“…Gene inactivation of either Fat4 or Dchs1 in mice results in a wide spectrum of phenotypes ranging from branching and cystic defects in the kidney, altered neuronal proliferation and migration, to a change in sternum shape (Saburi et al, 2008(Saburi et al, , 2012Mao et al, 2011Mao et al, , 2015Mao et al, , 2016Zakaria et al, 2014;Bagherie-Lachidan et al, 2015;Badouel et al, 2015). FAT4 and DCHS1 are also essential in humans, and compound mutations result in Van Maldergem syndrome, which is characterised, in part, by intellectual disability and altered craniofacial development (Cappello et al, 2013); in some individuals vertebral defects have also been reported (Mansour et al, 2012).…”