Actin depolymerizing factors cofilin1 and destrin are required for ureteric bud branching morphogenesis

Peer reviewe

Kidney Development in the Absence of Gdnf and Spry1 Requires Fgf10

GDNF signaling through the Ret receptor tyrosine kinase (RTK) is required for ureteric bud (UB) branching morphogenesis during kidney development in mice and humans. Furthermore, many other mutant genes that cause renal agenesis exert their effects via the GDNF/RET pathway. Therefore, RET signaling is believed to play a central role in renal organogenesis. Here, we re-examine the extent to which the functions of Gdnf and Ret are unique, by seeking conditions in which a kidney can develop in their absence. We find that in the absence of the negative regulator Spry1, Gdnf, and Ret are no longer required for extensive kidney development. Gdnf−/−;Spry1−/− or Ret−/−;Spry1−/− double mutants develop large kidneys with normal ureters, highly branched collecting ducts, extensive nephrogenesis, and normal histoarchitecture. However, despite extensive branching, the UB displays alterations in branch spacing, angle, and frequency. UB branching in the absence of Gdnf and Spry1 requires Fgf10 (which normally plays a minor role), as removal of even one copy of Fgf10 in Gdnf−/−;Spry1−/− mutants causes a complete failure of ureter and kidney development. In contrast to Gdnf or Ret mutations, renal agenesis caused by concomitant lack of the transcription factors ETV4 and ETV5 is not rescued by removing Spry1, consistent with their role downstream of both RET and FGFRs. This shows that, for many aspects of renal development, the balance between positive signaling by RTKs and negative regulation of this signaling by SPRY1 is more critical than the specific role of GDNF. Other signals, including FGF10, can perform many of the functions of GDNF, when SPRY1 is absent. But GDNF/RET signaling has an apparently unique function in determining normal branching pattern. In contrast to GDNF or FGF10, Etv4 and Etv5 represent a critical node in the RTK signaling network that cannot by bypassed by reducing the negative regulation of upstream signals

Kidney development in the absence of Gdnf and Spry1 requires Fgf10.

GDNF signaling through the Ret receptor tyrosine kinase (RTK) is required for ureteric bud (UB) branching morphogenesis during kidney development in mice and humans. Furthermore, many other mutant genes that cause renal agenesis exert their effects via the GDNF/RET pathway. Therefore, RET signaling is believed to play a central role in renal organogenesis. Here, we re-examine the extent to which the functions of Gdnf and Ret are unique, by seeking conditions in which a kidney can develop in their absence. We find that in the absence of the negative regulator Spry1, Gdnf, and Ret are no longer required for extensive kidney development. Gdnf-/-;Spry1-/- or Ret-/-;Spry1-/- double mutants develop large kidneys with normal ureters, highly branched collecting ducts, extensive nephrogenesis, and normal histoarchitecture. However, despite extensive branching, the UB displays alterations in branch spacing, angle, and frequency. UB branching in the absence of Gdnf and Spry1 requires Fgf10 (which normally plays a minor role), as removal of even one copy of Fgf10 in Gdnf-/-;Spry1-/- mutants causes a complete failure of ureter and kidney development. In contrast to Gdnf or Ret mutations, renal agenesis caused by concomitant lack of the transcription factors ETV4 and ETV5 is not rescued by removing Spry1, consistent with their role downstream of both RET and FGFRs. This shows that, for many aspects of renal development, the balance between positive signaling by RTKs and negative regulation of this signaling by SPRY1 is more critical than the specific role of GDNF. Other signals, including FGF10, can perform many of the functions of GDNF, when SPRY1 is absent. But GDNF/RET signaling has an apparently unique function in determining normal branching pattern. In contrast to GDNF or FGF10, Etv4 and Etv5 represent a critical node in the RTK signaling network that cannot by bypassed by reducing the negative regulation of upstream signals

Sproutv1, a wt1 target gene, anagonizes the action of, receptor tyrosine kinases

WT1 is a tumor suppressor gene with an essential role in the development of the kidney. In addition WT1 in expressed in hematopoietic progenitor cells and can inhibit hematopoietic cell growth. In a model system for WT1 action we found that in addition to inhibiting cell growth.WTl could induce features of epithelial differentiation in NIH 3T3 fibroblasts. Using this cell line model we performed representative difference analysis to isolate genes regulated by WT1. The genes isolated were then tested for their ability to be induced after transient transduction of naive 3T3 cells with a WT1-harboring retrovirus, their expression in a podocyte and mesonephric cell line and finally for their expression in the developing murine kidney. Among the genes meeting all these criteria was sprouty 1. Sprouty was originally isolated in Drosophila as an inhibitor of FGF signaling and branching morphogensis of the respiratory system of the fly. In order to understand the potential function of sprouty in organogenesis and tumor development, we established cells that conditionally expressed sprouty. Sproutyl as well as sprouty 2 inhibited growth of NIH 3T3 cells. Sprouty inhibited the activation of ERK by FGF and PDGF and inhibited the ability of growth factors to activate the ELK1, API and NFkB transcription factors. Inhibition of NFkB activity was specific to the PDGF and not the TNF pathway. While the RAS/RAF/MEK pathway was inhibited by sprouty, activation of AKT through the PI3 kinase pathway was not, again indicating a specific point of action of sprouty downstream of the receptor tyrosine kinase. In this regard, sprouty inhibited the activation of ERK, MEK and inhibited the binding of RAS to RAF. This suggest that sprouty either prevents the accumulation of GTP-RAS or inhibts the RAS/RAF interaction. These data indicate that sprouty is growth inhibitor downstream of WT1 whose expression in response to WT1 and growth factor signaling may limit proliferation during organ development and hematopoiesis

Branching morphogenesis of the ureteric epithelium during kidney development is coordinated by the opposing functions of GDNF and Sprouty1

AbstractBranching of ureteric bud-derived epithelial tubes is a key morphogenetic process that shapes development of the kidney. Glial cell line-derived neurotrophic factor (GDNF) initiates ureteric bud formation and promotes subsequent branching morphogenesis. Exactly how GDNF coordinates branching morphogenesis is unclear. Here we show that the absence of the receptor tyrosine kinase antagonist Sprouty1 (Spry1) results in irregular branching morphogenesis characterized by both increased number and size of ureteric bud tips. Deletion of Spry1 specifically in the epithelium is associated with increased epithelial Wnt11 expression as well as increased mesenchymal Gdnf expression. We propose that Spry1 regulates a Gdnf/Ret/Wnt11-positive feedback loop that coordinates mesenchymal–epithelial dialogue during branching morphogenesis. Genetic experiments indicate that the positive (GDNF) and inhibitory (Sprouty1) signals have to be finely balanced throughout renal development to prevent hypoplasia or cystic hyperplasia. Epithelial cysts develop in Spry1-deficient kidneys that share several molecular characteristics with those observed in human disease, suggesting that Spry1 null mice may be useful animal models for cystic hyperplasia